Programs & Examples On #Mutex

A mutex ("mutual exclusion") is a mechanism to ensure integrity when the same data or resource is accessed (in particular, changed) concurrently from several threads.

Mutex example / tutorial?

The function pthread_mutex_lock() either acquires the mutex for the calling thread or blocks the thread until the mutex can be acquired. The related pthread_mutex_unlock() releases the mutex.

Think of the mutex as a queue; every thread that attempts to acquire the mutex will be placed on the end of the queue. When a thread releases the mutex, the next thread in the queue comes off and is now running.

A critical section refers to a region of code where non-determinism is possible. Often this because multiple threads are attempting to access a shared variable. The critical section is not safe until some sort of synchronization is in place. A mutex lock is one form of synchronization.

Mutex lock threads

Below, code snippet, will help you in understanding the mutex-lock-unlock concept. Attempt dry-run on the code. (further by varying the wait-time and process-time, you can build you understanding).

Code for your reference:

#include <stdio.h>
#include <pthread.h>

void in_progress_feedback(int);

int global = 0;
pthread_mutex_t mutex;
void *compute(void *arg) {

    pthread_t ptid = pthread_self();
    printf("ptid : %08x \n", (int)ptid);    

    int i;
    int lock_ret = 1;   
    do{

        lock_ret = pthread_mutex_trylock(&mutex);
        if(lock_ret){
            printf("lock failed(%08x :: %d)..attempt again after 2secs..\n", (int)ptid,  lock_ret);
            sleep(2);  //wait time here..
        }else{  //ret =0 is successful lock
            printf("lock success(%08x :: %d)..\n", (int)ptid, lock_ret);
            break;
        }

    } while(lock_ret);

        for (i = 0; i < 10*10 ; i++) 
        global++;

    //do some stuff here
    in_progress_feedback(10);  //processing-time here..

    lock_ret = pthread_mutex_unlock(&mutex);
    printf("unlocked(%08x :: %d)..!\n", (int)ptid, lock_ret);

     return NULL;
}

void in_progress_feedback(int prog_delay){

    int i=0;
    for(;i<prog_delay;i++){
    printf(". ");
    sleep(1);
    fflush(stdout);
    }

    printf("\n");
    fflush(stdout);
}

int main(void)
{
    pthread_t tid0,tid1;
    pthread_mutex_init(&mutex, NULL);
    pthread_create(&tid0, NULL, compute, NULL);
    pthread_create(&tid1, NULL, compute, NULL);
    pthread_join(tid0, NULL);
    pthread_join(tid1, NULL);
    printf("global = %d\n", global);
    pthread_mutex_destroy(&mutex);
          return 0;
}

Proper use of mutexes in Python

I don't know why you're using the Window's Mutex instead of Python's. Using the Python methods, this is pretty simple:

from threading import Thread, Lock

mutex = Lock()

def processData(data):
    mutex.acquire()
    try:
        print('Do some stuff')
    finally:
        mutex.release()

while True:
    t = Thread(target = processData, args = (some_data,))
    t.start()

But note, because of the architecture of CPython (namely the Global Interpreter Lock) you'll effectively only have one thread running at a time anyway--this is fine if a number of them are I/O bound, although you'll want to release the lock as much as possible so the I/O bound thread doesn't block other threads from running.

An alternative, for Python 2.6 and later, is to use Python's multiprocessing package. It mirrors the threading package, but will create entirely new processes which can run simultaneously. It's trivial to update your example:

from multiprocessing import Process, Lock

mutex = Lock()

def processData(data):
    with mutex:
        print('Do some stuff')

if __name__ == '__main__':
    while True:
        p = Process(target = processData, args = (some_data,))
        p.start()

What is the Swift equivalent to Objective-C's "@synchronized"?

You can use GCD. It is a little more verbose than @synchronized, but works as a replacement:

let serialQueue = DispatchQueue(label: "com.test.mySerialQueue")
serialQueue.sync {
    // code
}

What is mutex and semaphore in Java ? What is the main difference?

This question has relevant answers and link to official Java guidance: Is there a Mutex in Java?

Is there a Mutex in Java?

To ensure that a Semaphore is binary you just need to make sure you pass in the number of permits as 1 when creating the semaphore. The Javadocs have a bit more explanation.

What is the correct way to create a single-instance WPF application?

Simply using a StreamWriter, how about this?

System.IO.File.StreamWriter OpenFlag = null;   //globally

and

try
{
    OpenFlag = new StreamWriter(Path.GetTempPath() + "OpenedIfRunning");
}
catch (System.IO.IOException) //file in use
{
    Environment.Exit(0);
}

What is a good pattern for using a Global Mutex in C#?

Sometimes learning by example helps the most. Run this console application in three different console windows. You'll see that the application you ran first acquires the mutex first, while the other two are waiting their turn. Then press enter in the first application, you'll see that application 2 now continues running by acquiring the mutex, however application 3 is waiting its turn. After you press enter in application 2 you'll see that application 3 continues. This illustrates the concept of a mutex protecting a section of code to be executed only by one thread (in this case a process) like writing to a file as an example.

using System;
using System.Threading;

namespace MutexExample
{
    class Program
    {
        static Mutex m = new Mutex(false, "myMutex");//create a new NAMED mutex, DO NOT OWN IT
        static void Main(string[] args)
        {
            Console.WriteLine("Waiting to acquire Mutex");
            m.WaitOne(); //ask to own the mutex, you'll be queued until it is released
            Console.WriteLine("Mutex acquired.\nPress enter to release Mutex");
            Console.ReadLine();
            m.ReleaseMutex();//release the mutex so other processes can use it
        }
    }
}

enter image description here

When should we use mutex and when should we use semaphore

All the above answers are of good quality,but this one's just to memorize.The name Mutex is derived from Mutually Exclusive hence you are motivated to think of a mutex lock as Mutual Exclusion between two as in only one at a time,and if I possessed it you can have it only after I release it.On the other hand such case doesn't exist for Semaphore is just like a traffic signal(which the word Semaphore also means).

Recursive Lock (Mutex) vs Non-Recursive Lock (Mutex)

The answer is not efficiency. Non-reentrant mutexes lead to better code.

Example: A::foo() acquires the lock. It then calls B::bar(). This worked fine when you wrote it. But sometime later someone changes B::bar() to call A::baz(), which also acquires the lock.

Well, if you don't have recursive mutexes, this deadlocks. If you do have them, it runs, but it may break. A::foo() may have left the object in an inconsistent state before calling bar(), on the assumption that baz() couldn't get run because it also acquires the mutex. But it probably shouldn't run! The person who wrote A::foo() assumed that nobody could call A::baz() at the same time - that's the entire reason that both of those methods acquired the lock.

The right mental model for using mutexes: The mutex protects an invariant. When the mutex is held, the invariant may change, but before releasing the mutex, the invariant is re-established. Reentrant locks are dangerous because the second time you acquire the lock you can't be sure the invariant is true any more.

If you are happy with reentrant locks, it is only because you have not had to debug a problem like this before. Java has non-reentrant locks these days in java.util.concurrent.locks, by the way.

What is a mutex?

Mutual Exclusion. Here's the Wikipedia entry on it.

The point of a mutex is to synchronize two threads. When you have two threads attempting to access a single resource, the general pattern is to have the first block of code attempting access to set the mutex before entering the code. When the second code block attempts access, it sees that the mutex is set and waits until the first block of code is complete (and unsets the mutex), then continues.

Specific details of how this is accomplished obviously varies greatly by programming language.

Difference between binary semaphore and mutex

Nice articles on the topic:

From part 2:

The mutex is similar to the principles of the binary semaphore with one significant difference: the principle of ownership. Ownership is the simple concept that when a task locks (acquires) a mutex only it can unlock (release) it. If a task tries to unlock a mutex it hasn’t locked (thus doesn’t own) then an error condition is encountered and, most importantly, the mutex is not unlocked. If the mutual exclusion object doesn't have ownership then, irrelevant of what it is called, it is not a mutex.

When should one use a spinlock instead of mutex?

Using spinlocks on a single-core/single-CPU system makes usually no sense, since as long as the spinlock polling is blocking the only available CPU core, no other thread can run and since no other thread can run, the lock won't be unlocked either. IOW, a spinlock wastes only CPU time on those systems for no real benefit

This is wrong. There is no wastage of cpu cycles in using spinlocks on uni processor systems, because once a process takes a spin lock , preemption is disabled , so as such, there could be no one else spinning! It's just that using it doesn't make any sense! Hence, spinlocks on Uni systems are replaced by preempt_disable at compile time by the kernel!

Example for boost shared_mutex (multiple reads/one write)?

Just to add some more empirical info, I have been investigating the whole issue of upgradable locks, and Example for boost shared_mutex (multiple reads/one write)? is a good answer adding the important info that only one thread can have an upgrade_lock even if it is not upgraded, that is important as it means you cannot upgrade from a shared lock to a unique lock without releasing the shared lock first. (This has been discussed elsewhere but the most interesting thread is here http://thread.gmane.org/gmane.comp.lib.boost.devel/214394)

However I did find an important (undocumented) difference between a thread waiting for an upgrade to a lock (ie needs to wait for all readers to release the shared lock) and a writer lock waiting for the same thing (ie a unique_lock).

  1. The thread that is waiting for a unique_lock on the shared_mutex blocks any new readers coming in, they have to wait for the writers request. This ensures readers do not starve writers (however I believe writers could starve readers).

  2. The thread that is waiting for an upgradeable_lock to upgrade allows other threads to get a shared lock, so this thread could be starved if readers are very frequent.

This is an important issue to consider, and probably should be documented.

Lock, mutex, semaphore... what's the difference?

My understanding is that a mutex is only for use within a single process, but across its many threads, whereas a semaphore may be used across multiple processes, and across their corresponding sets of threads.

Also, a mutex is binary (it's either locked or unlocked), whereas a semaphore has a notion of counting, or a queue of more than one lock and unlock requests.

Could someone verify my explanation? I'm speaking in the context of Linux, specifically Red Hat Enterprise Linux (RHEL) version 6, which uses kernel 2.6.32.

Trim to remove white space

No need for jQuery

JavaScript does have a native .trim() method.

var name = "    John Smith  ";
name = name.trim();

console.log(name); // "John Smith"

Example Here

String.prototype.trim()

The trim() method removes whitespace from both ends of a string. Whitespace in this context is all the whitespace characters (space, tab, no-break space, etc.) and all the line terminator characters (LF, CR, etc.).

Less aggressive compilation with CSS3 calc

A very common usecase of calc is take 100% width and adding some margin around the element.

One can do so with:

@someMarginVariable = 15px;

margin: @someMarginVariable;
width: calc(~"100% - "@someMarginVariable*2);
width: -moz-calc(~"100% - "@someMarginVariable*2);
width: -webkit-calc(~"100% - "@someMarginVariable*2);

Android Studio Error: Error:CreateProcess error=216, This version of %1 is not compatible with the version of Windows you're running

I had the same issue, but I have resolved it the next:

1) Install jdk1.8...

2) In AndroidStudio File->Project Structure->SDK Location, select your directory where the JDK is located, by default Studio uses embedded JDK but for some reason it produces error=216.

3) Click Ok.

How to find out which package version is loaded in R?

Search() can give a more simplified list of the attached packages in a session (i.e., without the detailed info given by sessionInfo())

search {base}- R Documentation
Description: Gives a list of attached packages. Search()

search()
#[1] ".GlobalEnv"        "package:Rfacebook" "package:httpuv"   
#"package:rjson"    
#[5] "package:httr"      "package:bindrcpp"  "package:forcats"   # 
#"package:stringr"  
#[9] "package:dplyr"     "package:purrr"     "package:readr"     
#"package:tidyr"    
#[13] "package:tibble"    "package:ggplot2"   "package:tidyverse" 
#"tools:rstudio"    
#[17] "package:stats"     "package:graphics"  "package:grDevices" 
#"package:utils"    
#[21] "package:datasets"  "package:methods"   "Autoloads"         
#"package:base"

Remove ALL white spaces from text

Regex for remove white space

\s+

_x000D_
_x000D_
var str = "Visit Microsoft!";
var res = str.replace(/\s+/g, "");
console.log(res);
_x000D_
_x000D_
_x000D_

or

[ ]+

_x000D_
_x000D_
var str = "Visit Microsoft!";
var res = str.replace(/[ ]+/g, "");
console.log(res);
_x000D_
_x000D_
_x000D_

Remove all white space at begin of string

^[ ]+

_x000D_
_x000D_
var str = "    Visit Microsoft!";
var res = str.replace(/^[ ]+/g, "");
console.log(res);
_x000D_
_x000D_
_x000D_

remove all white space at end of string

[ ]+$

_x000D_
_x000D_
var str = "Visit Microsoft!      ";
var res = str.replace(/[ ]+$/g, "");
console.log(res);
_x000D_
_x000D_
_x000D_

How to automatically select all text on focus in WPF TextBox?

Try putting this in the constructor of whatever control is housing your textbox:

Loaded += (sender, e) =>
{
    MoveFocus(new TraversalRequest(FocusNavigationDirection.Next));
    myTextBox.SelectAll();
}

Put Excel-VBA code in module or sheet?

I would suggest separating your code based on the functionality and purpose specific to each sheet or module. In this manner, you would only put code relative to a sheet's UI inside the sheet's module and only put code related to modules in respective modules. Also, use separate modules to encapsulate code that is shared or reused among several different sheets.

For example, let's say you multiple sheets that are responsible for displaying data from a database in a special way. What kinds of functionality do we have in this situation? We have functionality related to each specific sheet, tasks related to getting data from the database, and tasks related to populating a sheet with data. In this case, I might start with a module for the data access, a module for populating a sheet with data, and within each sheet I'd have code for accessing code in those modules.

It might be laid out like this.

Module: DataAccess:

Function GetData(strTableName As String, strCondition1 As String) As Recordset
    'Code Related to getting data from the database'
End Function

Module: PopulateSheet:

Sub PopulateASheet(wsSheet As Worksheet, rs As Recordset)
    'Code to populate a worksheet '
End Function

Sheet: Sheet1 Code:

Sub GetDataAndPopulate()
    'Sample Code'
     Dim rs As New Recordset
     Dim ws As Worksheet
     Dim strParam As String
     Set ws = ActiveSheet
     strParam = ws.Range("A1").Value

     Set rs = GetData("Orders",strParam)

     PopulateASheet ws, rs
End Sub

Sub Button1_Click()
    Call GetDataAndPopulate
End Sub

How to generate a Makefile with source in sub-directories using just one makefile

Usually, you create a Makefile in each subdirectory, and write in the top-level Makefile to call make in the subdirectories.

This page may help: http://www.gnu.org/software/make/

splitting a string into an array in C++ without using vector

#define MAXSPACE 25

string line =  "test one two three.";
string arr[MAXSPACE];
string search = " ";
int spacePos;
int currPos = 0;
int k = 0;
int prevPos = 0;

do
{

    spacePos = line.find(search,currPos);

    if(spacePos >= 0)
    {

        currPos = spacePos;
        arr[k] = line.substr(prevPos, currPos - prevPos);
        currPos++;
        prevPos = currPos;
        k++;
    }


}while( spacePos >= 0);

arr[k] = line.substr(prevPos,line.length());

for(int i = 0; i < k; i++)
{
   cout << arr[i] << endl;
}

Element count of an array in C++

Use the Microsoft "_countof(array)" Macro. This link to the Microsoft Developer Network explains it and offers an example that demonstrates the difference between "sizeof(array)" and the "_countof(array)" macro.

Microsoft and the "_countof(array)" Macro

Adding days to a date in Python

Generally you have'got an answer now but maybe my class I created will be also helpfull. For me it solves all my requirements I have ever had in my Pyhon projects.

class GetDate:
    def __init__(self, date, format="%Y-%m-%d"):
        self.tz = pytz.timezone("Europe/Warsaw")

        if isinstance(date, str):
            date = datetime.strptime(date, format)

        self.date = date.astimezone(self.tz)

    def time_delta_days(self, days):
        return self.date + timedelta(days=days)

    def time_delta_hours(self, hours):
        return self.date + timedelta(hours=hours)

    def time_delta_seconds(self, seconds):
        return self.date + timedelta(seconds=seconds)

    def get_minimum_time(self):
        return datetime.combine(self.date, time.min).astimezone(self.tz)

    def get_maximum_time(self):
        return datetime.combine(self.date, time.max).astimezone(self.tz)

    def get_month_first_day(self):
        return datetime(self.date.year, self.date.month, 1).astimezone(self.tz)

    def current(self):
        return self.date

    def get_month_last_day(self):
        lastDay = calendar.monthrange(self.date.year, self.date.month)[1]
        date = datetime(self.date.year, self.date.month, lastDay)
        return datetime.combine(date, time.max).astimezone(self.tz)

How to use it

  1. self.tz = pytz.timezone("Europe/Warsaw") - here you define Time Zone you want to use in project
  2. GetDate("2019-08-08").current() - this will convert your string date to time aware object with timezone you defined in pt 1. Default string format is format="%Y-%m-%d" but feel free to change it. (eg. GetDate("2019-08-08 08:45", format="%Y-%m-%d %H:%M").current())
  3. GetDate("2019-08-08").get_month_first_day() returns given date (string or object) month first day
  4. GetDate("2019-08-08").get_month_last_day() returns given date month last day
  5. GetDate("2019-08-08").minimum_time() returns given date day start
  6. GetDate("2019-08-08").maximum_time() returns given date day end
  7. GetDate("2019-08-08").time_delta_days({number_of_days}) returns given date + add {number of days} (you can also call: GetDate(timezone.now()).time_delta_days(-1) for yesterday)
  8. GetDate("2019-08-08").time_delta_haours({number_of_hours}) similar to pt 7 but working on hours
  9. GetDate("2019-08-08").time_delta_seconds({number_of_seconds}) similar to pt 7 but working on seconds

Changing line colors with ggplot()

color and fill are separate aesthetics. Since you want to modify the color you need to use the corresponding scale:

d + scale_color_manual(values=c("#CC6666", "#9999CC"))

is what you want.

How I could add dir to $PATH in Makefile?

To set the PATH variable, within the Makefile only, use something like:

PATH := $(PATH):/my/dir

test:
@echo my new PATH = $(PATH)

Automatically open Chrome developer tools when new tab/new window is opened

On a Mac: Quit Chrome, then run the following command in a terminal window:

open -a "Google Chrome" --args --auto-open-devtools-for-tabs

No provider for HttpClient

I had same issue. After browsing and struggling with issue found the below solution

import { HttpModule } from '@angular/http';
import { HttpClientModule } from '@angular/common/http';

imports: [
  HttpModule,
  HttpClientModule
]

Import HttpModule and HttpClientModule in app.module.ts and add into the imports like mentioned above.

How to fix "Incorrect string value" errors?

First check if your default_character_set_name is utf8.

SELECT default_character_set_name FROM information_schema.SCHEMATA S WHERE schema_name = "DBNAME";

If the result is not utf8 you must convert your database. At first you must save a dump.

To change the character set encoding to UTF-8 for all of the tables in the specified database, type the following command at the command line. Replace DBNAME with the database name:

mysql --database=DBNAME -B -N -e "SHOW TABLES" | awk '{print "SET foreign_key_checks = 0; ALTER TABLE", $1, "CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci; SET foreign_key_checks = 1; "}' | mysql --database=DBNAME

To change the character set encoding to UTF-8 for the database itself, type the following command at the mysql> prompt. Replace DBNAME with the database name:

ALTER DATABASE DBNAME CHARACTER SET utf8 COLLATE utf8_general_ci;

You can now retry to to write utf8 character into your database. This solution help me when i try to upload 200000 row of csv file into my database.

GitHub - List commits by author

Just add ?author=<emailaddress> or ?author=<githubUserName> to the url when viewing the "commits" section of a repo.

Action bar navigation modes are deprecated in Android L

The new Android Design Support Library adds TabLayout, providing a tab implementation that matches the material design guidelines for tabs. A complete walkthrough of how to implement Tabs and ViewPager can be found in this video

Now deprecated: The PagerTabStrip is part of the support library (and has been for some time) and serves as a direct replacement. If you prefer the newer Google Play style tabs, you can use the PagerSlidingTabStrip library or modify either of the Google provided examples SlidingTabsBasic or SlidingTabsColors as explained in this Dev Bytes video.

favicon not working in IE

Thanks for all your help.I tried different options but the below one worked for me.

<link rel="shortcut icon" href="/favicon.ico" >
<link rel="icon" type="/image/ico"  href="/favicon.ico" >

I have added the above two lines in the header of my page and it worked in all browsers.

Thanks

How to convert Double to int directly?

If you really should use Double instead of double you even can get the int Value of Double by calling:

Double d = new Double(1.23);
int i = d.intValue();

Else its already described by Peter Lawreys answer.

Best Practices for securing a REST API / web service

There is a great checklist found on Github:

Authentication

  • Don't reinvent the wheel in Authentication, token generation, password storage. Use the standards.

  • Use Max Retry and jail features in Login.

  • Use encryption on all sensitive data.

JWT (JSON Web Token)

  • Use a random complicated key (JWT Secret) to make brute forcing the token very hard.

  • Don't extract the algorithm from the payload. Force the algorithm in the backend (HS256 or RS256).

  • Make token expiration (TTL, RTTL) as short as possible.

  • Don't store sensitive data in the JWT payload, it can be decoded easily.

OAuth

  • Always validate redirect_uri server-side to allow only whitelisted URLs.

  • Always try to exchange for code and not tokens (don't allow response_type=token).

  • Use state parameter with a random hash to prevent CSRF on the OAuth authentication process.

  • Define the default scope, and validate scope parameters for each application.

Access

  • Limit requests (Throttling) to avoid DDoS / brute-force attacks.

  • Use HTTPS on server side to avoid MITM (Man In The Middle Attack)

  • Use HSTS header with SSL to avoid SSL Strip attack.

Input

  • Use the proper HTTP method according to the operation: GET (read), POST (create), PUT/PATCH (replace/update), and DELETE (to delete a record), and respond with 405 Method Not Allowed if the requested method isn't appropriate for the requested resource.

  • Validate content-type on request Accept header (Content Negotiation) to allow only your supported format (e.g. application/xml, application/json, etc) and respond with 406 Not Acceptable response if not matched.

  • Validate content-type of posted data as you accept (e.g. application/x-www-form-urlencoded, multipart/form-data, application/json, etc).

  • Validate User input to avoid common vulnerabilities (e.g. XSS, SQL-Injection, Remote Code Execution, etc).

  • Don't use any sensitive data (credentials, Passwords, security tokens, or API keys) in the URL, but use standard Authorization header.

  • Use an API Gateway service to enable caching, Rate Limit policies (e.g. Quota, Spike Arrest, Concurrent Rate Limit) and deploy APIs resources dynamically.

Processing

  • Check if all the endpoints are protected behind authentication to avoid broken authentication process.

  • User own resource ID should be avoided. Use /me/orders instead of /user/654321/orders.

  • Don't auto-increment IDs. Use UUID instead.

  • If you are parsing XML files, make sure entity parsing is not enabled to avoid XXE (XML external entity attack).

  • If you are parsing XML files, make sure entity expansion is not enabled to avoid Billion Laughs/XML bomb via exponential entity expansion attack.

  • Use a CDN for file uploads.

  • If you are dealing with huge amount of data, use Workers and Queues to process as much as possible in background and return response fast to avoid HTTP Blocking.

  • Do not forget to turn the DEBUG mode OFF.

Output

  • Send X-Content-Type-Options: nosniff header.

  • Send X-Frame-Options: deny header.

  • Send Content-Security-Policy: default-src 'none' header.

  • Remove fingerprinting headers - X-Powered-By, Server, X-AspNet-Version etc.

  • Force content-type for your response, if you return application/json then your response content-type is application/json.

  • Don't return sensitive data like credentials, Passwords, security tokens.

  • Return the proper status code according to the operation completed. (e.g. 200 OK, 400 Bad Request, 401 Unauthorized, 405 Method Not Allowed, etc).

Use of "this" keyword in C++

It's programmer preference. Personally, I love using this since it explicitly marks the object members. Of course the _ does the same thing (only when you follow the convention)

Why boolean in Java takes only true or false? Why not 1 or 0 also?

One thing that other answers haven't pointed out is that one advantage of not treating integers as truth values is that it avoids this C / C++ bug syndrome:

int i = 0;
if (i = 1) {
    print("the sky is falling!\n");
} 

In C / C++, the mistaken use of = rather than == causes the condition to unexpectedly evaluate to "true" and update i as an accidental side-effect.

In Java, that is a compilation error, because the value of the assigment i = 1 has type int and a boolean is required at that point. The only case where you'd get into trouble in Java is if you write lame code like this:

boolean ok = false;
if (ok = true) {  // bug and lame style
    print("the sky is falling!\n");
}

... which anyone with an ounce of "good taste" would write as ...

boolean ok = false;
if (ok) {
    print("the sky is falling!\n");
}

Customize Bootstrap checkboxes

Here you have an example styling checkboxes and radios using Font Awesome 5 free[

_x000D_
_x000D_
  /*General style*/_x000D_
  .custom-checkbox label, .custom-radio label {_x000D_
    position: relative;_x000D_
    cursor: pointer;_x000D_
    color: #666;_x000D_
    font-size: 30px;_x000D_
  }_x000D_
 .custom-checkbox input[type="checkbox"] ,.custom-radio input[type="radio"] {_x000D_
    position: absolute;_x000D_
    right: 9000px;_x000D_
  }_x000D_
   /*Custom checkboxes style*/_x000D_
  .custom-checkbox input[type="checkbox"]+.label-text:before {_x000D_
    content: "\f0c8";_x000D_
    font-family: "Font Awesome 5 Pro";_x000D_
    speak: none;_x000D_
    font-style: normal;_x000D_
    font-weight: normal;_x000D_
    font-variant: normal;_x000D_
    text-transform: none;_x000D_
    line-height: 1;_x000D_
    -webkit-font-smoothing: antialiased;_x000D_
    width: 1em;_x000D_
    display: inline-block;_x000D_
    margin-right: 5px;_x000D_
  }_x000D_
  .custom-checkbox input[type="checkbox"]:checked+.label-text:before {_x000D_
    content: "\f14a";_x000D_
    color: #2980b9;_x000D_
    animation: effect 250ms ease-in;_x000D_
  }_x000D_
  .custom-checkbox input[type="checkbox"]:disabled+.label-text {_x000D_
    color: #aaa;_x000D_
  }_x000D_
  .custom-checkbox input[type="checkbox"]:disabled+.label-text:before {_x000D_
    content: "\f0c8";_x000D_
    color: #ccc;_x000D_
  }_x000D_
_x000D_
   /*Custom checkboxes style*/_x000D_
  .custom-radio input[type="radio"]+.label-text:before {_x000D_
    content: "\f111";_x000D_
    font-family: "Font Awesome 5 Pro";_x000D_
    speak: none;_x000D_
    font-style: normal;_x000D_
    font-weight: normal;_x000D_
    font-variant: normal;_x000D_
    text-transform: none;_x000D_
    line-height: 1;_x000D_
    -webkit-font-smoothing: antialiased;_x000D_
    width: 1em;_x000D_
    display: inline-block;_x000D_
    margin-right: 5px;_x000D_
  }_x000D_
_x000D_
  .custom-radio input[type="radio"]:checked+.label-text:before {_x000D_
    content: "\f192";_x000D_
    color: #8e44ad;_x000D_
    animation: effect 250ms ease-in;_x000D_
  }_x000D_
_x000D_
  .custom-radio input[type="radio"]:disabled+.label-text {_x000D_
    color: #aaa;_x000D_
  }_x000D_
_x000D_
  .custom-radio input[type="radio"]:disabled+.label-text:before {_x000D_
    content: "\f111";_x000D_
    color: #ccc;_x000D_
  }_x000D_
_x000D_
  @keyframes effect {_x000D_
    0% {_x000D_
      transform: scale(0);_x000D_
    }_x000D_
    25% {_x000D_
      transform: scale(1.3);_x000D_
    }_x000D_
    75% {_x000D_
      transform: scale(1.4);_x000D_
    }_x000D_
    100% {_x000D_
      transform: scale(1);_x000D_
    }_x000D_
  }
_x000D_
<script src="https://kit.fontawesome.com/2a10ab39d6.js"></script>_x000D_
<div class="col-md-4">_x000D_
  <form>_x000D_
    <h2>1. Customs Checkboxes</h2>_x000D_
    <div class="custom-checkbox">_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="checkbox" name="check" checked> <span class="label-text">Option 01</span>_x000D_
                </label>_x000D_
      </div>_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="checkbox" name="check"> <span class="label-text">Option 02</span>_x000D_
                </label>_x000D_
      </div>_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="checkbox" name="check"> <span class="label-text">Option 03</span>_x000D_
                </label>_x000D_
      </div>_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="checkbox" name="check" disabled> <span class="label-text">Option 04</span>_x000D_
                </label>_x000D_
      </div>_x000D_
    </div>_x000D_
  </form>_x000D_
</div>_x000D_
<div class="col-md-4">_x000D_
  <form>_x000D_
    <h2>2. Customs Radios</h2>_x000D_
    <div class="custom-radio">_x000D_
_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="radio" name="radio" checked> <span class="label-text">Option 01</span>_x000D_
                </label>_x000D_
      </div>_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="radio" name="radio"> <span class="label-text">Option 02</span>_x000D_
                </label>_x000D_
      </div>_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="radio" name="radio"> <span class="label-text">Option 03</span>_x000D_
                </label>_x000D_
      </div>_x000D_
      <div class="form-check">_x000D_
        <label>_x000D_
                    <input type="radio" name="radio" disabled> <span class="label-text">Option 04</span>_x000D_
                </label>_x000D_
      </div>_x000D_
    </div>_x000D_
  </form>_x000D_
</div>
_x000D_
_x000D_
_x000D_

Attach the Source in Eclipse of a jar

Eclipse is showing no source found because there is no source available . Your jar only has the compiled classes.

You need to import the project from jar and add the Project as dependency .

Other option is to go to the

Go to Properties (for the Project) -> Java Build Path -> Libraries , select your jar file and click on the source , there will be option to attach the source and Javadocs.

Best way to store date/time in mongodb

One datestamp is already in the _id object, representing insert time

So if the insert time is what you need, it's already there:

Login to mongodb shell

ubuntu@ip-10-0-1-223:~$ mongo 10.0.1.223
MongoDB shell version: 2.4.9
connecting to: 10.0.1.223/test

Create your database by inserting items

> db.penguins.insert({"penguin": "skipper"})
> db.penguins.insert({"penguin": "kowalski"})
> 

Lets make that database the one we are on now

> use penguins
switched to db penguins

Get the rows back:

> db.penguins.find()
{ "_id" : ObjectId("5498da1bf83a61f58ef6c6d5"), "penguin" : "skipper" }
{ "_id" : ObjectId("5498da28f83a61f58ef6c6d6"), "penguin" : "kowalski" }

Get each row in yyyy-MM-dd HH:mm:ss format:

> db.penguins.find().forEach(function (doc){ d = doc._id.getTimestamp(); print(d.getFullYear()+"-"+(d.getMonth()+1)+"-"+d.getDate() + " " + d.getHours() + ":" + d.getMinutes() + ":" + d.getSeconds()) })
2014-12-23 3:4:41
2014-12-23 3:4:53

If that last one-liner confuses you I have a walkthrough on how that works here: https://stackoverflow.com/a/27613766/445131

How to get highcharts dates in the x axis?

Check this sample out from the Highcharts API.

Replace this

return Highcharts.dateFormat('%a %d %b', this.value);

With this

return Highcharts.dateFormat('%a %d %b %H:%M:%S', this.value);

Look here about the dateFormat() function.

Also see - tickInterval and pointInterval

VBA Macro to compare all cells of two Excel files

Do NOT loop through all cells!! There is a lot of overhead in communications between worksheets and VBA, for both reading and writing. Looping through all cells will be agonizingly slow. I'm talking hours.

Instead, load an entire sheet at once into a Variant array. In Excel 2003, this takes about 2 seconds (and 250 MB of RAM). Then you can loop through it in no time at all.

In Excel 2007 and later, sheets are about 1000 times larger (1048576 rows × 16384 columns = 17 billion cells, compared to 65536 rows × 256 columns = 17 million in Excel 2003). You will run into an "Out of memory" error if you try to load the whole sheet into a Variant; on my machine I can only load 32 million cells at once. So you have to limit yourself to the range you know has actual data in it, or load the sheet bit by bit, e.g. 30 columns at a time.

Option Explicit

Sub test()

    Dim varSheetA As Variant
    Dim varSheetB As Variant
    Dim strRangeToCheck As String
    Dim iRow As Long
    Dim iCol As Long

    strRangeToCheck = "A1:IV65536"
    ' If you know the data will only be in a smaller range, reduce the size of the ranges above.
    Debug.Print Now
    varSheetA = Worksheets("Sheet1").Range(strRangeToCheck)
    varSheetB = Worksheets("Sheet2").Range(strRangeToCheck) ' or whatever your other sheet is.
    Debug.Print Now

    For iRow = LBound(varSheetA, 1) To UBound(varSheetA, 1)
        For iCol = LBound(varSheetA, 2) To UBound(varSheetA, 2)
            If varSheetA(iRow, iCol) = varSheetB(iRow, iCol) Then
                ' Cells are identical.
                ' Do nothing.
            Else
                ' Cells are different.
                ' Code goes here for whatever it is you want to do.
            End If
        Next iCol
    Next iRow

End Sub

To compare to a sheet in a different workbook, open that workbook and get the sheet as follows:

Set wbkA = Workbooks.Open(filename:="C:\MyBook.xls")
Set varSheetA = wbkA.Worksheets("Sheet1") ' or whatever sheet you need

Direct download from Google Drive using Google Drive API

I faced an issue in direct download because I was logged in using multiple Google accounts. Solution is append authUser=0 parameter. Sample request URL to download :https://drive.google.com/uc?id=FILEID&authuser=0&export=download

Using jQuery UI sortable with HTML tables

You can call sortable on a <tbody> instead of on the individual rows.

<table>
    <tbody>
        <tr> 
            <td>1</td>
            <td>2</td>
        </tr>
        <tr>
            <td>3</td>
            <td>4</td> 
        </tr>
        <tr>
            <td>5</td>
            <td>6</td>
        </tr>  
    </tbody>    
</table>?

<script>
    $('tbody').sortable();
</script> 

_x000D_
_x000D_
$(function() {_x000D_
  $( "tbody" ).sortable();_x000D_
});
_x000D_
 _x000D_
table {_x000D_
    border-spacing: collapse;_x000D_
    border-spacing: 0;_x000D_
}_x000D_
td {_x000D_
    width: 50px;_x000D_
    height: 25px;_x000D_
    border: 1px solid black;_x000D_
}
_x000D_
 _x000D_
_x000D_
<link href="//code.jquery.com/ui/1.11.1/themes/smoothness/jquery-ui.css" rel="stylesheet">_x000D_
<script src="//code.jquery.com/jquery-1.11.1.js"></script>_x000D_
<script src="//code.jquery.com/ui/1.11.1/jquery-ui.js"></script>_x000D_
_x000D_
<table>_x000D_
    <tbody>_x000D_
        <tr>_x000D_
            <td>1</td>_x000D_
            <td>2</td>_x000D_
        </tr>_x000D_
        <tr>_x000D_
            <td>3</td>_x000D_
            <td>4</td>_x000D_
        </tr>_x000D_
        <tr> _x000D_
            <td>5</td>_x000D_
            <td>6</td>_x000D_
        </tr>_x000D_
        <tr>_x000D_
            <td>7</td>_x000D_
            <td>8</td>_x000D_
        </tr>_x000D_
        <tr>_x000D_
            <td>9</td> _x000D_
            <td>10</td>_x000D_
        </tr>  _x000D_
    </tbody>    _x000D_
</table>
_x000D_
_x000D_
_x000D_

When should I use "this" in a class?

There are a lot of good answers, but there is another very minor reason to put this everywhere. If you have tried opening your source codes from a normal text editor (e.g. notepad etc), using this will make it a whole lot clearer to read.

Imagine this:

public class Hello {
    private String foo;

    // Some 10k lines of codes

    private String getStringFromSomewhere() {
        // ....
    }

    // More codes

    public class World {
        private String bar;

        // Another 10k lines of codes

        public void doSomething() {
            // More codes
            foo = "FOO";
            // More codes
            String s = getStringFromSomewhere();
            // More codes
            bar = s;
        }
    }
}

This is very clear to read with any modern IDE, but this will be a total nightmare to read with a regular text editor.

You will struggle to find out where foo resides, until you use the editor's "find" function. Then you will scream at getStringFromSomewhere() for the same reason. Lastly, after you have forgotten what s is, that bar = s is going to give you the final blow.

Compare it to this:

public void doSomething() {
    // More codes
    Hello.this.foo = "FOO";
    // More codes
    String s = Hello.this.getStringFromSomewhere();
    // More codes
    this.bar = s;
}
  1. You know foo is a variable declared in outer class Hello.
  2. You know getStringFromSomewhere() is a method declared in outer class as well.
  3. You know that bar belongs to World class, and s is a local variable declared in that method.

Of course, whenever you design something, you create rules. So while designing your API or project, if your rules include "if someone opens all these source codes with a notepad, he or she should shoot him/herself in the head," then you are totally fine not to do this.

How to hide the border for specified rows of a table?

Use the CSS property border on the <td>s following the <tr>s you do not want to have the border.

In my example I made a class noBorder that I gave to one <tr>. Then I use a simple selector tr.noBorder td to make the border go away for all the <td>s that are inside of <tr>s with the noBorder class by assigning border: 0.

Note that you do not need to provide the unit (i.e. px) if you set something to 0 as it does not matter anyway. Zero is just zero.

_x000D_
_x000D_
table, tr, td {_x000D_
  border: 3px solid red;_x000D_
}_x000D_
tr.noBorder td {_x000D_
  border: 0;_x000D_
}
_x000D_
<table>_x000D_
  <tr>_x000D_
    <td>A1</td>_x000D_
    <td>B1</td>_x000D_
    <td>C1</td>_x000D_
  </tr>_x000D_
  <tr class="noBorder">_x000D_
    <td>A2</td>_x000D_
    <td>B2</td>_x000D_
    <td>C2</td>_x000D_
  </tr>_x000D_
  <tr>_x000D_
    <td>A3</td>_x000D_
    <td>A3</td>_x000D_
    <td>A3</td>_x000D_
  </tr>_x000D_
</table>
_x000D_
_x000D_
_x000D_

Here's the output as an image:

Output from HTML

Remove an item from array using UnderscoreJS

or another handy way:

_.omit(arr, _.findWhere(arr, {id: 3}));

my 2 cents

How do I make a delay in Java?

Using TimeUnit.SECONDS.sleep(1); or Thread.sleep(1000); Is acceptable way to do it. In both cases you have to catch InterruptedExceptionwhich makes your code Bulky.There is an Open Source java library called MgntUtils (written by me) that provides utility that already deals with InterruptedException inside. So your code would just include one line:

TimeUtils.sleepFor(1, TimeUnit.SECONDS);

See the javadoc here. You can access library from Maven Central or from Github. The article explaining about the library could be found here

How to use enums in C++

If we want the strict type safety and scoped enum, using enum class is good in C++11.

If we had to work in C++98, we can using the advice given by InitializeSahib,San to enable the scoped enum.

If we also want the strict type safety, the follow code can implement somthing like enum.

#include <iostream>
class Color
{
public:
    static Color RED()
    {
        return Color(0);
    }
    static Color BLUE()
    {
        return Color(1);
    }
    bool operator==(const Color &rhs) const
    {
        return this->value == rhs.value;
    }
    bool operator!=(const Color &rhs) const
    {
        return !(*this == rhs);
    }

private:
    explicit Color(int value_) : value(value_) {}
    int value;
};

int main()
{
    Color color = Color::RED();
    if (color == Color::RED())
    {
        std::cout << "red" << std::endl;
    }
    return 0;
}

The code is modified from the class Month example in book Effective C++ 3rd: Item 18

Check if a number is int or float

variable.isnumeric checks if a value is an integer:

 if myVariable.isnumeric:
    print('this varibale is numeric')
 else:
    print('not numeric')

How to fix Ora-01427 single-row subquery returns more than one row in select?

(SELECT C.I_WORKDATE
         FROM T_COMPENSATION C
         WHERE C.I_COMPENSATEDDATE = A.I_REQDATE AND ROWNUM <= 1
         AND C.I_EMPID = A.I_EMPID)

Creating and Naming Worksheet in Excel VBA

Are you committing the cell before pressing the button (pressing Enter)? The contents of the cell must be stored before it can be used to name a sheet.

A better way to do this is to pop up a dialog box and get the name you wish to use.

How to Generate unique file names in C#

Why can't we make a unique id as below.

We can use DateTime.Now.Ticks and Guid.NewGuid().ToString() to combine together and make a unique id.

As the DateTime.Now.Ticks is added, we can find out the Date and Time in seconds at which the unique id is created.

Please see the code.

var ticks = DateTime.Now.Ticks;
var guid = Guid.NewGuid().ToString();
var uniqueSessionId = ticks.ToString() +'-'+ guid; //guid created by combining ticks and guid

var datetime = new DateTime(ticks);//for checking purpose
var datetimenow = DateTime.Now;    //both these date times are different.

We can even take the part of ticks in unique id and check for the date and time later for future reference.

You can attach the unique id created to the filename or can be used for creating unique session id for login-logout of users to our application or website.

Verilog generate/genvar in an always block

for verilog just do

parameter ROWBITS = 4;
reg [ROWBITS-1:0] temp;
always @(posedge sysclk) begin
  temp <= {ROWBITS{1'b0}}; // fill with 0
end

Python can't find module in the same folder

If you are sure that all the modules, files you're trying to import are in the same folder and they should be picked directly just by giving the name and not the reference path then your editor or terminal should have opened the main folder where all the files/modules are present.

Either, try running from Terminal, make sure first you go to the correct directory.

cd path to the root folder where all the modules are

python script.py

Or if running [F5] from the editor i.e VsCode then open the complete folder there and not the individual files.

Drop all data in a pandas dataframe

You need to pass the labels to be dropped.

df.drop(df.index, inplace=True)

By default, it operates on axis=0.

You can achieve the same with

df.iloc[0:0]

which is much more efficient.

Python: How to check if keys exists and retrieve value from Dictionary in descending priority

If we encapsulate that in a function we could use recursion and state clearly the purpose by naming the function properly (not sure if getAny is actually a good name):

def getAny(dic, keys, default=None):
    return (keys or default) and dic.get(keys[0], 
                                         getAny( dic, keys[1:], default=default))

or even better, without recursion and more clear:

def getAny(dic, keys, default=None):
    for k in keys: 
        if k in dic:
           return dic[k]
    return default

Then that could be used in a way similar to the dict.get method, like:

getAny(myDict, keySet)

and even have a default result in case of no keys found at all:

getAny(myDict, keySet, "not found")

How to print Unicode character in Python?

I use Portable winpython in Windows, it includes IPython QT console, I could achieve the following.

>>>print ("??")
??

>>>print ("????")
????

>>>str = "??"


>>>print (str)
??

your console interpreter should support unicode in order to show unicode characters.

How to create Temp table with SELECT * INTO tempTable FROM CTE Query

Here's one slight alteration to the answers of a query that creates the table upon execution (i.e. you don't have to create the table first):

SELECT * INTO #Temp
FROM (
select OptionNo, OptionName from Options where OptionActive = 1
) as X

Retrieving a Foreign Key value with django-rest-framework serializers

Worked on 08/08/2018 and on DRF version 3.8.2:

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.ReadOnlyField(source='category.name')

    class Meta:
        model = Item
        read_only_fields = ('id', 'category_name')
        fields = ('id', 'category_name', 'name',)

Using the Meta read_only_fields we can declare exactly which fields should be read_only. Then we need to declare the foreign field on the Meta fields (better be explicit as the mantra goes: zen of python).

TypeScript - Append HTML to container element in Angular 2

1.

<div class="one" [innerHtml]="htmlToAdd"></div>
this.htmlToAdd = '<div class="two">two</div>';

See also In RC.1 some styles can't be added using binding syntax

  1. Alternatively
<div class="one" #one></div>
@ViewChild('one') d1:ElementRef;

ngAfterViewInit() {
  d1.nativeElement.insertAdjacentHTML('beforeend', '<div class="two">two</div>');
}

or to prevent direct DOM access:

constructor(private renderer:Renderer) {}

@ViewChild('one') d1:ElementRef;

ngAfterViewInit() {
  this.renderer.invokeElementMethod(this.d1.nativeElement', 'insertAdjacentHTML' ['beforeend', '<div class="two">two</div>']);
}
    3.
constructor(private elementRef:ElementRef) {}

ngAfterViewInit() {
  var d1 = this.elementRef.nativeElement.querySelector('.one');
  d1.insertAdjacentHTML('beforeend', '<div class="two">two</div>');
}

How do I check to see if a value is an integer in MySQL?

This also works:

CAST( coulmn_value AS UNSIGNED ) // will return 0 if not numeric string.

for example

SELECT CAST('a123' AS UNSIGNED) // returns 0
SELECT CAST('123' AS UNSIGNED) // returns 123 i.e. > 0

How can I query for null values in entity framework?

to deal with Null Comparisons use Object.Equals() instead of ==

check this reference

How to make a <button> in Bootstrap look like a normal link in nav-tabs?

Just add remove_button_css as class to your button tag. You can verify the code for Link 1

.remove_button_css { 
  outline: none;
  padding: 5px; 
  border: 0px; 
  box-sizing: none; 
  background-color: transparent; 
}

enter image description here

Extra Styles Edit

Add color: #337ab7; and :hover and :focus to match OOTB (bootstrap3)

.remove_button_css:focus,
.remove_button_css:hover {
    color: #23527c;
    text-decoration: underline;
}

OAuth: how to test with local URLs?

Taking Google OAuth as reference

  • In your OAuth client Tab

    1. Add your App URI example(http://localhost:3000) to Authorized JavaScript origins URIs
  • In your OAuth consent screen

    1. Add mywebsite.com to Authorized domains
  • Edit the hosts file on windows or linux Windows C:\Windows\System32\Drivers\etc\hosts Linux : /etc/hosts to add 127.0.0.1 mywebsite.com (N.B. Comment out any if there is any other 127.0.0.1)

how to create a window with two buttons that will open a new window

You add your ActionListener twice to button. So correct your code for button2 to

  JButton button2 = new JButton("hello agin2");
  panel.add(button2);
  button2.addActionListener (new Action2());//note the button2 here instead of button

Furthermore, perform your Swing operations on the correct thread by using EventQueue.invokeLater

Get installed applications in a system

The object for the list:

public class InstalledProgram
{
    public string DisplayName { get; set; }
    public string Version { get; set; }
    public string InstalledDate { get; set; }
    public string Publisher { get; set; }
    public string UnninstallCommand { get; set; }
    public string ModifyPath { get; set; }
}

The call for creating the list:

    List<InstalledProgram> installedprograms = new List<InstalledProgram>();
    string registry_key = @"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall";
    using (RegistryKey key = Registry.LocalMachine.OpenSubKey(registry_key))
    {
        foreach (string subkey_name in key.GetSubKeyNames())
        {
            using (RegistryKey subkey = key.OpenSubKey(subkey_name))
            {
                if (subkey.GetValue("DisplayName") != null)
                {
                    installedprograms.Add(new InstalledProgram
                    {
                        DisplayName = (string)subkey.GetValue("DisplayName"),
                        Version = (string)subkey.GetValue("DisplayVersion"),
                        InstalledDate = (string)subkey.GetValue("InstallDate"),
                        Publisher = (string)subkey.GetValue("Publisher"),
                        UnninstallCommand = (string)subkey.GetValue("UninstallString"),
                        ModifyPath = (string)subkey.GetValue("ModifyPath")
                    });
                }
            }
        }
    }

What is {this.props.children} and when you should use it?

props.children represents the content between the opening and the closing tags when invoking/rendering a component:

const Foo = props => (
  <div>
    <p>I'm {Foo.name}</p>
    <p>abc is: {props.abc}</p>

    <p>I have {props.children.length} children.</p>
    <p>They are: {props.children}.</p>
    <p>{Array.isArray(props.children) ? 'My kids are an array.' : ''}</p>
  </div>
);

const Baz = () => <span>{Baz.name} and</span>;
const Bar = () => <span> {Bar.name}</span>;

invoke/call/render Foo:

<Foo abc={123}>
  <Baz />
  <Bar />
</Foo>

props and props.children

how much memory can be accessed by a 32 bit machine?

basically 32bit architecture can address 4GB as you expected. There are some techniques which allows processor to address more data like AWE or PAE.

Comparing mongoose _id and strings

ObjectIDs are objects so if you just compare them with == you're comparing their references. If you want to compare their values you need to use the ObjectID.equals method:

if (results.userId.equals(AnotherMongoDocument._id)) {
    ...
}

Null & empty string comparison in Bash

fedorqui has a working solution but there is another way to do the same thing.

Chock if a variable is set

#!/bin/bash
amIEmpty='Hello'
# This will be true if the variable has a value
if [ $amIEmpty ]; then
    echo 'No, I am not!';
fi

Or to verify that a variable is empty

#!/bin/bash      
amIEmpty=''
# This will be true if the variable is empty
if [ ! $amIEmpty ]; then
    echo 'Yes I am!';
fi

tldp.org has good documentation about if in bash:
http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html

SQL Server FOR EACH Loop

Off course an old question. But I have a simple solution where no need of Looping, CTE, Table variables etc.

DECLARE @MyVar datetime = '1/1/2010'    
SELECT @MyVar

SELECT DATEADD (DD,NUMBER,@MyVar) 
FROM master.dbo.spt_values 
WHERE TYPE='P' AND NUMBER BETWEEN 0 AND 4 
ORDER BY NUMBER

Note : spt_values is a Mircrosoft's undocumented table. It has numbers for every type. Its not suggestible to use as it can be removed in any new versions of sql server without prior information, since it is undocumented. But we can use it as quick workaround in some scenario's like above.

How to Insert BOOL Value to MySQL Database

TRUE and FALSE are keywords, and should not be quoted as strings:

INSERT INTO first VALUES (NULL, 'G22', TRUE);
INSERT INTO first VALUES (NULL, 'G23', FALSE);

By quoting them as strings, MySQL will then cast them to their integer equivalent (since booleans are really just a one-byte INT in MySQL), which translates into zero for any non-numeric string. Thus, you get 0 for both values in your table.

Non-numeric strings cast to zero:

mysql> SELECT CAST('TRUE' AS SIGNED), CAST('FALSE' AS SIGNED), CAST('12345' AS SIGNED);
+------------------------+-------------------------+-------------------------+
| CAST('TRUE' AS SIGNED) | CAST('FALSE' AS SIGNED) | CAST('12345' AS SIGNED) |
+------------------------+-------------------------+-------------------------+
|                      0 |                       0 |                   12345 |
+------------------------+-------------------------+-------------------------+

But the keywords return their corresponding INT representation:

mysql> SELECT TRUE, FALSE;
+------+-------+
| TRUE | FALSE |
+------+-------+
|    1 |     0 |
+------+-------+

Note also, that I have replaced your double-quotes with single quotes as are more standard SQL string enclosures. Finally, I have replaced your empty strings for id with NULL. The empty string may issue a warning.

Import Excel spreadsheet columns into SQL Server database

The import wizard does offer that option. You can either use the option to write your own query for the data to import, or you can use the copy data option and use the "Edit Mappings" button to ignore columns you do not want to import.

Download file from an ASP.NET Web API method using AngularJS

I have gone through array of solutions and this is what I found to have worked great for me.

In my case I needed to send a post request with some credentials. Small overhead was to add jquery inside the script. But was worth it.

var printPDF = function () {
        //prevent double sending
        var sendz = {};
        sendz.action = "Print";
        sendz.url = "api/Print";
        jQuery('<form action="' + sendz.url + '" method="POST">' +
            '<input type="hidden" name="action" value="Print" />'+
            '<input type="hidden" name="userID" value="'+$scope.user.userID+'" />'+
            '<input type="hidden" name="ApiKey" value="' + $scope.user.ApiKey+'" />'+
            '</form>').appendTo('body').submit().remove();

    }

SQL : BETWEEN vs <= and >=

As mentioned by @marc_s, @Cloud, et al. they're basically the same for a closed range.

But any fractional time values may cause issues with a closed range (greater-or-equal and less-or-equal) as opposed to a half-open range (greater-or-equal and less-than) with an end value after the last possible instant.

So to avoid that the query should be rewritten as:

SELECT EventId, EventName
  FROM EventMaster
 WHERE (EventDate >= '2009-10-15' AND
        EventDate <  '2009-10-19')    /* <<<== 19th, not 18th */

Since BETWEEN doesn't work for half-open intervals I always take a hard look at any date/time query that uses it, since its probably an error.

How do you programmatically update query params in react-router?

From DimitriDushkin on GitHub:

import { browserHistory } from 'react-router';

/**
 * @param {Object} query
 */
export const addQuery = (query) => {
  const location = Object.assign({}, browserHistory.getCurrentLocation());

  Object.assign(location.query, query);
  // or simple replace location.query if you want to completely change params

  browserHistory.push(location);
};

/**
 * @param {...String} queryNames
 */
export const removeQuery = (...queryNames) => {
  const location = Object.assign({}, browserHistory.getCurrentLocation());
  queryNames.forEach(q => delete location.query[q]);
  browserHistory.push(location);
};

or

import { withRouter } from 'react-router';
import { addQuery, removeQuery } from '../../utils/utils-router';

function SomeComponent({ location }) {
  return <div style={{ backgroundColor: location.query.paintRed ? '#f00' : '#fff' }}>
    <button onClick={ () => addQuery({ paintRed: 1 })}>Paint red</button>
    <button onClick={ () => removeQuery('paintRed')}>Paint white</button>
  </div>;
}

export default withRouter(SomeComponent);

How to find path of active app.config file?

Strictly speaking, there is no single configuration file. Excluding ASP.NET1 there can be three configuration files using the inbuilt (System.Configuration) support. In addition to the machine config: app.exe.config, user roaming, and user local.

To get the "global" configuration (exe.config):

ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
                    .FilePath

Use different ConfigurationUserLevel values for per-use roaming and non-roaming configuration files.


1 Which has a completely different model where the content of a child folders (IIS-virtual or file system) web.config can (depending on the setting) add to or override the parent's web.config.

Hashing a file in Python

For the correct and efficient computation of the hash value of a file (in Python 3):

  • Open the file in binary mode (i.e. add 'b' to the filemode) to avoid character encoding and line-ending conversion issues.
  • Don't read the complete file into memory, since that is a waste of memory. Instead, sequentially read it block by block and update the hash for each block.
  • Eliminate double buffering, i.e. don't use buffered IO, because we already use an optimal block size.
  • Use readinto() to avoid buffer churning.

Example:

import hashlib

def sha256sum(filename):
    h  = hashlib.sha256()
    b  = bytearray(128*1024)
    mv = memoryview(b)
    with open(filename, 'rb', buffering=0) as f:
        for n in iter(lambda : f.readinto(mv), 0):
            h.update(mv[:n])
    return h.hexdigest()

Can we set a Git default to fetch all tags during a remote pull?

The --force option is useful for refreshing the local tags. Mainly if you have floating tags:

git fetch --tags --force

The git pull option has also the --force options, and the description is the same:

When git fetch is used with <rbranch>:<lbranch> refspec, it refuses to update the local branch <lbranch> unless the remote branch <rbranch> it fetches is a descendant of <lbranch>. This option overrides that check.

but, according to the doc of --no-tags:

By default, tags that point at objects that are downloaded from the remote repository are fetched and stored locally.

If that default statement is not a restriction, then you can also try

git pull --force

Generate signed apk android studio

Official Android Documentation on the matter at hand with a step-by-step guide included on how to generate signed APK keys in Android Studio and even on how to setup the automatic APK key generation in a Gradle build.

https://developer.android.com/studio/publish/app-signing.html

Look under the chapter: Sign your release build

set the iframe height automatically

If the sites are on separate domains, the calling page can't access the height of the iframe due to cross-browser domain restrictions. If you have access to both sites, you may be able to use the [document domain hack].1 Then anroesti's links should help.

Insert and set value with max()+1 problems

SELECT MAX(col) +1 is not safe -- it does not ensure that you aren't inserting more than one customer with the same customer_id value, regardless if selecting from the same table or any others. The proper way to ensure a unique integer value is assigned on insertion into your table in MySQL is to use AUTO_INCREMENT. The ANSI standard is to use sequences, but MySQL doesn't support them. An AUTO_INCREMENT column can only be defined in the CREATE TABLE statement:

CREATE TABLE `customers` (
  `customer_id` int(11) NOT NULL AUTO_INCREMENT,
  `firstname` varchar(45) DEFAULT NULL,
  `surname` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`customer_id`)
)

That said, this worked fine for me on 5.1.49:

CREATE TABLE `customers` (
  `customer_id` int(11) NOT NULL DEFAULT '0',
  `firstname` varchar(45) DEFAULT NULL,
  `surname` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`customer_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$

INSERT INTO customers VALUES (1, 'a', 'b');

INSERT INTO customers 
SELECT MAX(customer_id) + 1, 'jim', 'sock'
  FROM CUSTOMERS;

An "and" operator for an "if" statement in Bash

Quote:

The "-a" operator also doesn't work:

if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]]

For a more elaborate explanation: [ and ] are not Bash reserved words. The if keyword introduces a conditional to be evaluated by a job (the conditional is true if the job's return value is 0 or false otherwise).

For trivial tests, there is the test program (man test).

As some find lines like if test -f filename; then foo bar; fi, etc. annoying, on most systems you find a program called [ which is in fact only a symlink to the test program. When test is called as [, you have to add ] as the last positional argument.

So if test -f filename is basically the same (in terms of processes spawned) as if [ -f filename ]. In both cases the test program will be started, and both processes should behave identically.

Here's your mistake: if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]] will parse to if + some job, the job being everything except the if itself. The job is only a simple command (Bash speak for something which results in a single process), which means the first word ([) is the command and the rest its positional arguments. There are remaining arguments after the first ].

Also not, [[ is indeed a Bash keyword, but in this case it's only parsed as a normal command argument, because it's not at the front of the command.

How do I put my website's logo to be the icon image in browser tabs?

  1. ADD THIS
**<HEAD>**

  < link rel="icon" href="directory/image.png">

Then run and enjoy it

Response.Redirect with POST instead of Get?

The GET (and HEAD) method should never be used to do anything that has side-effects. A side-effect might be updating the state of a web application, or it might be charging your credit card. If an action has side-effects another method (POST) should be used instead.

So, a user (or their browser) shouldn't be held accountable for something done by a GET. If some harmful or expensive side-effect occurred as the result of a GET, that would be the fault of the web application, not the user. According to the spec, a user agent must not automatically follow a redirect unless it is a response to a GET or HEAD request.

Of course, a lot of GET requests do have some side-effects, even if it's just appending to a log file. The important thing is that the application, not the user, should be held responsible for those effects.

The relevant sections of the HTTP spec are 9.1.1 and 9.1.2, and 10.3.

How to describe "object" arguments in jsdoc?

By now there are 4 different ways to document objects as parameters/types. Each has its own uses. Only 3 of them can be used to document return values, though.

For objects with a known set of properties (Variant A)

/**
 * @param {{a: number, b: string, c}} myObj description
 */

This syntax is ideal for objects that are used only as parameters for this function and don't require further description of each property. It can be used for @returns as well.

For objects with a known set of properties (Variant B)

Very useful is the parameters with properties syntax:

/**
 * @param {Object} myObj description
 * @param {number} myObj.a description
 * @param {string} myObj.b description
 * @param {} myObj.c description
 */

This syntax is ideal for objects that are used only as parameters for this function and that require further description of each property. This can not be used for @returns.

For objects that will be used at more than one point in source

In this case a @typedef comes in very handy. You can define the type at one point in your source and use it as a type for @param or @returns or other JSDoc tags that can make use of a type.

/**
 * @typedef {Object} Person
 * @property {string} name how the person is called
 * @property {number} age how many years the person lived
 */

You can then use this in a @param tag:

/**
 * @param {Person} p - Description of p
 */

Or in a @returns:

/**
 * @returns {Person} Description
 */

For objects whose values are all the same type

/**
 * @param {Object.<string, number>} dict
 */

The first type (string) documents the type of the keys which in JavaScript is always a string or at least will always be coerced to a string. The second type (number) is the type of the value; this can be any type. This syntax can be used for @returns as well.

Resources

Useful information about documenting types can be found here:

https://jsdoc.app/tags-type.html

PS:

to document an optional value you can use []:

/**
 * @param {number} [opt_number] this number is optional
 */

or:

/**
 * @param {number|undefined} opt_number this number is optional
 */

php create object without class

you can always use new stdClass(). Example code:

   $object = new stdClass();
   $object->property = 'Here we go';

   var_dump($object);
   /*
   outputs:

   object(stdClass)#2 (1) {
      ["property"]=>
      string(10) "Here we go"
    }
   */

Also as of PHP 5.4 you can get same output with:

$object = (object) ['property' => 'Here we go'];

Returning a boolean from a Bash function

Use 0 for true and 1 for false.

Sample:

#!/bin/bash

isdirectory() {
  if [ -d "$1" ]
  then
    # 0 = true
    return 0 
  else
    # 1 = false
    return 1
  fi
}


if isdirectory $1; then echo "is directory"; else echo "nopes"; fi

Edit

From @amichair's comment, these are also possible

isdirectory() {
  if [ -d "$1" ]
  then
    true
  else
    false
  fi
}


isdirectory() {
  [ -d "$1" ]
}

Using a dispatch_once singleton model in Swift

First solution

let SocketManager = SocketManagerSingleton();

class SocketManagerSingleton {

}

Later in your code:

func someFunction() {        
    var socketManager = SocketManager        
}

Second solution

func SocketManager() -> SocketManagerSingleton {
    return _SocketManager
}
let _SocketManager = SocketManagerSingleton();

class SocketManagerSingleton {

}

And later in your code you will be able to keep braces for less confusion:

func someFunction() {        
    var socketManager = SocketManager()        
}

Convert Java Array to Iterable

You can use IterableOf from Cactoos:

Iterable<String> names = new IterableOf<>(
  "Scott Fitzgerald", "Fyodor Dostoyevsky"
);

Then, you can turn it into a list using ListOf:

List<String> names = new ListOf<>(
  new IterableOf<>(
    "Scott Fitzgerald", "Fyodor Dostoyevsky"
  )
);

Or simply this:

List<String> names = new ListOf<>(
  "Scott Fitzgerald", "Fyodor Dostoyevsky"
);

Insert array into MySQL database with PHP

I search about the same problem, but I wanted to store the array in a filed not to add the array as a tuple, so you may need the function serialize() and unserialize().

See this http://www.wpfasthelp.com/insert-php-array-into-mysql-database-table-row-field.htm

Change the size of a JTextField inside a JBorderLayout

From the api on GridLayout:

The container is divided into equal-sized rectangles, and one component is placed in each rectangle.

Try using FlowLayout or GridBagLayout for your set size to be meaningful. Also, @Serplat is correct. You need to use setPreferredSize( Dimension ) instead of setSize( int, int ).

    JPanel displayPanel = new JPanel();
    // JPanel displayPanel = new JPanel( new GridLayout( 4, 2 ) );
    // JPanel displayPanel = new JPanel( new BorderLayout() );
    // JPanel displayPanel = new JPanel( new GridBagLayout() );

    JTextField titleText = new JTextField( "title" );

    titleText.setPreferredSize( new Dimension( 200, 24 ) );

    // For FlowLayout and GridLayout, uncomment:
    displayPanel.add( titleText );

    // For BorderLayout, uncomment:
    // displayPanel.add( titleText, BorderLayout.NORTH );

    // For GridBagLayout, uncomment:
    // displayPanel.add( titleText, new GridBagConstraints( 0, 0, 1, 1, 1.0,
    // 1.0, GridBagConstraints.CENTER, GridBagConstraints.NONE,
    // new Insets( 0, 0, 0, 0 ), 0, 0 ) );

Why should we include ttf, eot, woff, svg,... in a font-face

Woff is a compressed (zipped) form of the TrueType - OpenType font. It is small and can be delivered over the network like a graphic file. Most importantly, this way the font is preserved completely including rendering rule tables that very few people care about because they use only Latin script.

Take a look at [dead URL removed]. The font you see is an experimental web delivered smartfont (woff) that has thousands of combined characters making complex shapes. The underlying text is simple Latin code of romanized Singhala. (Copy and paste to Notepad and see).

Only woff can do this because nobody has this font and yet it is seen anywhere (Mac, Win, Linux and even on smartphones by all browsers except by IE. IE does not have full support for Open Types).

AngularJs - ng-model in a SELECT

You can also put the item with the default value selected out of the ng-repeat like follow :

<div ng-app="app" ng-controller="myCtrl">
    <select class="form-control" ng-change="unitChanged()" ng-model="data.unit">
        <option value="yourDefaultValue">Default one</option>
        <option ng-selected="data.unit == item.id" ng-repeat="item in units" ng-value="item.id">{{item.label}}</option>
    </select>
</div>

and don't forget the value atribute if you leave it blank you will have the same issue.

How do I undo 'git add' before commit?

git reset filename.txt

Will remove a file named filename.txt from the current index, the "about to be committed" area, without changing anything else.

What is the difference between PUT, POST and PATCH?

Quite logical the difference between PUT & PATCH w.r.t sending full & partial data for replacing/updating respectively. However, just couple of points as below

  1. Sometimes POST is considered as for updates w.r.t PUT for create
  2. Does HTTP mandates/checks for sending full vs partial data in PATCH? Otherwise, PATCH may be quite same as update as in PUT/POST

Load image from resources

You can add an image resource in the project then (right click on the project and choose the Properties item) access that in this way:

this.picturebox.image = projectname.properties.resources.imagename;

exporting multiple modules in react.js

When you

import App from './App.jsx';

That means it will import whatever you export default. You can rename App class inside App.jsx to whatever you want as long as you export default it will work but you can only have one export default.

So you only need to export default App and you don't need to export the rest.

If you still want to export the rest of the components, you will need named export.

https://developer.mozilla.org/en/docs/web/javascript/reference/statements/export

Binding multiple events to a listener (without JQuery)?

ES2015:

let el = document.getElementById("el");
let handler =()=> console.log("changed");
['change', 'keyup', 'cut'].forEach(event => el.addEventListener(event, handler));

Get a list of distinct values in List

public class KeyNote
{
    public long KeyNoteId { get; set; }
    public long CourseId { get; set; }
    public string CourseName { get; set; }
    public string Note { get; set; }
    public DateTime CreatedDate { get; set; }
}

public List<KeyNote> KeyNotes { get; set; }
public List<RefCourse> GetCourses { get; set; }    

List<RefCourse> courses = KeyNotes.Select(x => new RefCourse { CourseId = x.CourseId, Name = x.CourseName }).Distinct().ToList();

By using the above logic, we can get the unique Courses.

How to know installed Oracle Client is 32 bit or 64 bit?

One thing that was super easy and worked well for me was doing a TNSPing from a cmd prompt:

TNS Ping Utility for 32-bit Windows: Version 11.2.0.3.0 - Production on 13-MAR-2015 16:35:32

No converter found capable of converting from type to type

Simple Solution::

use {nativeQuery=true} in your query.

for example

  @Query(value = "select d.id,d.name,d.breed,d.origin from Dog d",nativeQuery = true)
        
    List<Dog> findALL();

How to change JAVA.HOME for Eclipse/ANT

Simply, to enforce JAVA version to Ant in Eclipse:

Use RunAs option on Ant file then select External Tool Configuration in JRE tab define your JDK/JRE version you want to use.

Add rows to CSV File in powershell

To simply append to a file in powershell,you can use add-content.

So, to only add a new line to the file, try the following, where $YourNewDate and $YourDescription contain the desired values.

$NewLine = "{0},{1}" -f $YourNewDate,$YourDescription
$NewLine | add-content -path $file

Or,

"{0},{1}" -f $YourNewDate,$YourDescription | add-content -path $file

This will just tag the new line to the end of the .csv, and will not work for creating new .csv files where you will need to add the header.

Difficulty with ng-model, ng-repeat, and inputs

The problem seems to be in the way how ng-model works with input and overwrites the name object, making it lost for ng-repeat.

As a workaround, one can use the following code:

<div ng-repeat="name in names">
    Value: {{name}}
    <input ng-model="names[$index]">                         
</div>

Hope it helps

Editing hosts file to redirect url?

No, but you could open a web server at, for example, 127.0.0.77 and use it to check if the Request URI is "/welcome.aspx"... If yes redirect to google, if not load the original site.

127.0.0.77      mysite.com

Is ncurses available for windows?

Such a thing probably does not exist "as-is". It doesn't really exist on Linux or other UNIX-like operating systems either though.

ncurses is only a library that helps you manage interactions with the underlying terminal environment. But it doesn't provide a terminal emulator itself.

The thing that actually displays stuff on the screen (which in your requirement is listed as "native resizable win32 windows") is usually called a Terminal Emulator. If you don't like the one that comes with Windows (you aren't alone; no person on Earth does) there are a few alternatives. There is Console, which in my experience works sometimes and appears to just wrap an underlying Windows terminal emulator (I don't know for sure, but I'm guessing, since there is a menu option to actually get access to that underlying terminal emulator, and sure enough an old crusty Windows/DOS box appears which mirrors everything in the Console window).

A better option

Another option, which may be more appealing is puttycyg. It hooks in to Putty (which, coming from a Linux background, is pretty close to what I'm used to, and free) but actually accesses an underlying cygwin instead of the Windows command interpreter (CMD.EXE). So you get all the benefits of Putty's awesome terminal emulator, as well as nice ncurses (and many other) libraries provided by cygwin. Add a couple command line arguments to the Shortcut that launches Putty (or the Batch file) and your app can be automatically launched without going through Putty's UI.

Insert json file into mongodb

Open command prompt separately and check:

C:\mongodb\bin\mongoimport --db db_name --collection collection_name< filename.json

How to output oracle sql result into a file in windows?

Very similar to Marc, only difference I would make would be to spool to a parameter like so:

WHENEVER SQLERROR EXIT 1
SET LINES 32000
SET TERMOUT OFF ECHO OFF NEWP 0 SPA 0 PAGES 0 FEED OFF HEAD OFF TRIMS ON TAB OFF
SET SERVEROUTPUT ON

spool &1

-- Code

spool off
exit

And then to call the SQLPLUS as

sqlplus -s username/password@sid @tmp.sql /tmp/output.txt

What is the difference between `new Object()` and object literal notation?

Actually, there are several ways to create objects in JavaScript. When you just want to create an object there's no benefit of creating "constructor-based" objects using "new" operator. It's same as creating an object using "object literal" syntax. But "constructor-based" objects created with "new" operator comes to incredible use when you are thinking about "prototypal inheritance". You cannot maintain inheritance chain with objects created with literal syntax. But you can create a constructor function, attach properties and methods to its prototype. Then if you assign this constructor function to any variable using "new" operator, it will return an object which will have access to all of the methods and properties attached with the prototype of that constructor function.

Here is an example of creating an object using constructor function (see code explanation at the bottom):

function Person(firstname, lastname) {
    this.firstname = firstname;
    this.lastname = lastname;
}

Person.prototype.fullname = function() {
    console.log(this.firstname + ' ' + this.lastname);
}

var zubaer = new Person('Zubaer', 'Ahammed');
var john = new Person('John', 'Doe');

zubaer.fullname();
john.fullname();

Now, you can create as many objects as you want by instantiating Person construction function and all of them will inherit fullname() from it.

Note: "this" keyword will refer to an empty object within a constructor function and whenever you create a new object from Person using "new" operator it will automatically return an object containing all of the properties and methods attached with the "this" keyword. And these object will for sure inherit the methods and properties attached with the prototype of the Person constructor function (which is the main advantage of this approach).

By the way, if you wanted to obtain the same functionality with "object literal" syntax, you would have to create fullname() on all of the objects like below:

var zubaer = {
    firstname: 'Zubaer',
    lastname: 'Ahammed',
    fullname: function() {
        console.log(this.firstname + ' ' + this.lastname);
    }
};

var john= {
    firstname: 'John',
    lastname: 'Doe',
    fullname: function() {
        console.log(this.firstname + ' ' + this.lastname);
    }
};

zubaer.fullname();
john.fullname();

At last, if you now ask why should I use constructor function approach instead of object literal approach:

*** Prototypal inheritance allows a simple chain of inheritance which can be immensely useful and powerful.

*** It saves memory by inheriting common methods and properties defined in constructor functions prototype. Otherwise, you would have to copy them over and over again in all of the objects.

I hope this makes sense.

Undefined Symbols for architecture x86_64: Compiling problems

There's no mystery here, the linker is telling you that you haven't defined the missing symbols, and you haven't.

Similarity::Similarity() or Similarity::~Similarity() are just missing and you have defined the others incorrectly,

void Similarity::readData(Scanner& inStream){
}

not

void readData(Scanner& inStream){
}

etc. etc.

The second one is a function called readData, only the first is the readData method of the Similarity class.

To be clear about this, in Similarity.h

void readData(Scanner& inStream);

but in Similarity.cpp

void Similarity::readData(Scanner& inStream){
}

Setting up a websocket on Apache?

I can't answer all questions, but I will do my best.

As you already know, WS is only a persistent full-duplex TCP connection with framed messages where the initial handshaking is HTTP-like. You need some server that's listening for incoming WS requests and that binds a handler to them.

Now it might be possible with Apache HTTP Server, and I've seen some examples, but there's no official support and it gets complicated. What would Apache do? Where would be your handler? There's a module that forwards incoming WS requests to an external shared library, but this is not necessary with the other great tools to work with WS.

WS server trends now include: Autobahn (Python) and Socket.IO (Node.js = JavaScript on the server). The latter also supports other hackish "persistent" connections like long polling and all the COMET stuff. There are other little known WS server frameworks like Ratchet (PHP, if you're only familiar with that).

In any case, you will need to listen on a port, and of course that port cannot be the same as the Apache HTTP Server already running on your machine (default = 80). You could use something like 8080, but even if this particular one is a popular choice, some firewalls might still block it since it's not supposed to be Web traffic. This is why many people choose 443, which is the HTTP Secure port that, for obvious reasons, firewalls do not block. If you're not using SSL, you can use 80 for HTTP and 443 for WS. The WS server doesn't need to be secure; we're just using the port.

Edit: According to Iharob Al Asimi, the previous paragraph is wrong. I have no time to investigate this, so please see his work for more details.

About the protocol, as Wikipedia shows, it looks like this:

Client sends:

GET /mychat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
Sec-WebSocket-Protocol: chat
Sec-WebSocket-Version: 13
Origin: http://example.com

Server replies:

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: chat

and keeps the connection alive. If you can implement this handshaking and the basic message framing (encapsulating each message with a small header describing it), then you can use any client-side language you want. JavaScript is only used in Web browsers because it's built-in.

As you can see, the default "request method" is an initial HTTP GET, although this is not really HTTP and looses everything in common with HTTP after this handshaking. I guess servers that do not support

Upgrade: websocket
Connection: Upgrade

will reply with an error or with a page content.

Create an empty object in JavaScript with {} or new Object()?

Objects

There is no benefit to using new Object(); - whereas {}; can make your code more compact, and more readable.

For defining empty objects they're technically the same. The {} syntax is shorter, neater (less Java-ish), and allows you to instantly populate the object inline - like so:

var myObject = {
        title:  'Frog',
        url:    '/img/picture.jpg',
        width:  300,
        height: 200
      };

Arrays

For arrays, there's similarly almost no benefit to ever using new Array(); over []; - with one minor exception:

var emptyArray = new Array(100);

creates a 100 item long array with all slots containing undefined - which may be nice/useful in certain situations (such as (new Array(9)).join('Na-Na ') + 'Batman!').

My recommendation

  1. Never use new Object(); - it's clunkier than {}; and looks silly.
  2. Always use []; - except when you need to quickly create an "empty" array with a predefined length.

How to export a table dataframe in PySpark to csv?

For Apache Spark 2+, in order to save dataframe into single csv file. Use following command

query.repartition(1).write.csv("cc_out.csv", sep='|')

Here 1 indicate that I need one partition of csv only. you can change it according to your requirements.

Loop through JSON in EJS

JSON.stringify returns a String. So, for example:

var data = [
    { id: 1, name: "bob" },
    { id: 2, name: "john" },
    { id: 3, name: "jake" },
];

JSON.stringify(data)

will return the equivalent of:

"[{\"id\":1,\"name\":\"bob\"},{\"id\":2,\"name\":\"john\"},{\"id\":3,\"name\":\"jake\"}]"

as a String value.

So when you have

<% for(var i=0; i<JSON.stringify(data).length; i++) {%>

what that ends up looking like is:

<% for(var i=0; i<"[{\"id\":1,\"name\":\"bob\"},{\"id\":2,\"name\":\"john\"},{\"id\":3,\"name\":\"jake\"}]".length; i++) {%>

which is probably not what you want. What you probably do want is something like this:

<table>
<% for(var i=0; i < data.length; i++) { %>
   <tr>
     <td><%= data[i].id %></td>
     <td><%= data[i].name %></td>
   </tr>
<% } %>
</table>

This will output the following table (using the example data from above):

<table>
  <tr>
    <td>1</td>
    <td>bob</td>
  </tr>
  <tr>
    <td>2</td>
    <td>john</td>
  </tr>
  <tr>
    <td>3</td>
    <td>jake</td>
  </tr>
</table>

Swift presentViewController

You can use code:

if let vc = self.storyboard?.instantiateViewController(withIdentifier: "secondViewController") as? secondViewController {
   let appDelegate = UIApplication.shared.delegate as! AppDelegate
   appDelegate.window?.rootViewController = vc
}

How to add elements to a list in R (loop)

The following adds elements to a list in a loop.

l<-c()
i=1

while(i<100) {

    b<-i
    l<-c(l,b)
    i=i+1
}

how to apply click event listener to image in android

Try this example.

activity_main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

<GridView
    android:numColumns="auto_fit"
    android:gravity="center"
    android:columnWidth="100dp"
    android:stretchMode="columnWidth"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/grid"
    android:background="#fff7ff"
    />

    </LinearLayout>

grid_single.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:padding="5dp" >

    <ImageView
        android:id="@+id/grid_image"
        android:layout_width="60dp"
        android:layout_height="60dp"

        >
    </ImageView>

    <TextView
        android:id="@+id/grid_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="15dp"
        android:textSize="9sp"
        android:textColor="#3a0fff">
    </TextView>

</LinearLayout>

CustomGrid.java:

package com.example.lalit.gridtest;

import android.content.Context;
        import android.view.LayoutInflater;
        import android.view.View;
        import android.view.ViewGroup;
        import android.widget.BaseAdapter;
        import android.widget.ImageView;
        import android.widget.TextView;

public class CustomGrid extends BaseAdapter {
    private Context mContext;
    private final String[] web;
    private final int[] Imageid;

    public CustomGrid(Context c, String[] web, int[] Imageid) {
        mContext = c;
        this.Imageid = Imageid;
        this.web = web;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return web.length;
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        View grid;
        LayoutInflater inflater = (LayoutInflater) mContext
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if (convertView == null) {

            grid = new View(mContext);
            grid = inflater.inflate(R.layout.grid_single, null);
            TextView textView = (TextView) grid.findViewById(R.id.grid_text);
            ImageView imageView = (ImageView) grid.findViewById(R.id.grid_image);
            textView.setText(web[position]);
            imageView.setImageResource(Imageid[position]);
        } else {
            grid = (View) convertView;
        }

        return grid;
    }
}

MainActivity.java:

package com.example.lalit.gridtest;

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {
    GridView grid;
    String[] web = {
            "Mom",
            "Mahendra",
            "Narayan",
            "Bhai",
            "Deepak",
            "Sanjay",
            "Navdeep",
            "Lovesh",


    };
    int[] imageId = {
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher

    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final CustomGrid adapter = new CustomGrid(MainActivity.this, web, imageId);
        grid = (GridView) findViewById(R.id.grid);
        grid.setAdapter(adapter);
        grid.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id){

                if (web[position].toString().equals("Mom")) {
                    try {
                        String uri ="te:"+ "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }
                }


                    if (web[position].toString().equals("Mahendra")) {
                        try {
                            String uri = "tel:" + "**********";

                            Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                            startActivity(callIntent);
                        } catch (Exception e) {
                            Toast.makeText(getApplicationContext(), "Your call has failed...",
                                    Toast.LENGTH_LONG).show();
                            e.printStackTrace();

                        }
                    }


                      if(web[position].toString().equals("Narayan")){

                    try {
                        String uri = "tel:" + "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }


             }
                if(web[position].toString().equals("Bhai")){

                    try {
                        String uri = "tel:" + "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }


                }

                if(web[position].toString().equals("Deepak")){

                    try {
                        String uri = "tel:" + "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }


                }


                if(web[position].toString().equals("Sanjay")){

                    try {
                        String uri = "tel:" + "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }


                }
                if(web[position].toString().equals("Navdeep")){

                    try {
                        String uri = "tel:" + "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }


                }
                if(web[position].toString().equals("Lovesh")){

                    try {
                        String uri = "tel:" + "**********";

                        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri));
                        startActivity(callIntent);
                    } catch (Exception e) {
                        Toast.makeText(getApplicationContext(), "Your call has failed...",
                                Toast.LENGTH_LONG).show();
                        e.printStackTrace();

                    }


                }

                }



        });

    }

    }

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.lalit.gridtest" >
    <uses-permission android:name="android.permission.CALL_PHONE" />
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

How to access SOAP services from iPhone

Here is a swift 4 sample code which execute API calling using SOAP service format.

   func callSOAPWSToGetData() {

        let strSOAPMessage =
            "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                "<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">" +
                "<soap:Body>" +
                "<CelsiusToFahrenheit xmlns=\"http://www.yourapi.com/webservices/\">" +
                "<Celsius>50</Celsius>" +
                "</CelsiusToFahrenheit>" +
                "</soap:Body>" +
        "</soap:Envelope>"

        guard let url = URL.init(string: "http://www.example.org") else {
            return
        }
        var request = URLRequest.init(url: url)
        let length = (strSOAPMessage as NSString).length
        request.addValue("application/soap+xml; charset=utf-8", forHTTPHeaderField: "Content-Type")
        request.addValue("http://www.yourapi.com/webservices/CelsiusToFahrenheit", forHTTPHeaderField: "SOAPAction")
        request.addValue(String(length), forHTTPHeaderField: "Content-Length")
        request.httpMethod = "POST"
        request.httpBody = strSOAPMessage.data(using: .utf8)

        let config = URLSessionConfiguration.default
        let session = URLSession(configuration: config)
        let task = session.dataTask(with: request) { (data, response, error) in
            guard let responseData = data else {
                print("Error: did not receive data")
                return
            }
            guard error == nil else {
                print("error calling GET on /todos/1")
                print(error ?? "")
                return
            }
            print(responseData)
            let strData = String.init(data: responseData, encoding: .utf8)
            print(strData ?? "")
        }
        task.resume()
    }

Integrate ZXing in Android Studio

buttion.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new com.google.zxing.integration.android.IntentIntegrator(Fragment.this).initiateScan();
            }
        });

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if(result != null) {
            if(result.getContents() == null) {
                Log.d("MainActivity", "Cancelled scan");
                Toast.makeText(this, "Cancelled", Toast.LENGTH_LONG).show();
            } else {
                Log.d("MainActivity", "Scanned");
                Toast.makeText(this, "Scanned: " + result.getContents(), Toast.LENGTH_LONG).show();
            }
        } else {
            // This is important, otherwise the result will not be passed to the fragment
            super.onActivityResult(requestCode, resultCode, data);
        }
    }



dependencies {
    compile 'com.journeyapps:zxing-android-embedded:3.2.0@aar'
    compile 'com.google.zxing:core:3.2.1'
    compile 'com.android.support:appcompat-v7:23.1.0'
}

Determining the version of Java SDK on the Mac

Open a terminal and type: java -version, or javac -version.

If you have all the latest updates for Snow Leopard, you should be running JDK 1.6.0_20 at this moment (the same as Oracle's current JDK version).

Multiprocessing vs Threading Python

Python documentation quotes

The canonical version of this answer is now at the dupliquee question: What are the differences between the threading and multiprocessing modules?

I've highlighted the key Python documentation quotes about Process vs Threads and the GIL at: What is the global interpreter lock (GIL) in CPython?

Process vs thread experiments

I did a bit of benchmarking in order to show the difference more concretely.

In the benchmark, I timed CPU and IO bound work for various numbers of threads on an 8 hyperthread CPU. The work supplied per thread is always the same, such that more threads means more total work supplied.

The results were:

enter image description here

Plot data.

Conclusions:

  • for CPU bound work, multiprocessing is always faster, presumably due to the GIL

  • for IO bound work. both are exactly the same speed

  • threads only scale up to about 4x instead of the expected 8x since I'm on an 8 hyperthread machine.

    Contrast that with a C POSIX CPU-bound work which reaches the expected 8x speedup: What do 'real', 'user' and 'sys' mean in the output of time(1)?

    TODO: I don't know the reason for this, there must be other Python inefficiencies coming into play.

Test code:

#!/usr/bin/env python3

import multiprocessing
import threading
import time
import sys

def cpu_func(result, niters):
    '''
    A useless CPU bound function.
    '''
    for i in range(niters):
        result = (result * result * i + 2 * result * i * i + 3) % 10000000
    return result

class CpuThread(threading.Thread):
    def __init__(self, niters):
        super().__init__()
        self.niters = niters
        self.result = 1
    def run(self):
        self.result = cpu_func(self.result, self.niters)

class CpuProcess(multiprocessing.Process):
    def __init__(self, niters):
        super().__init__()
        self.niters = niters
        self.result = 1
    def run(self):
        self.result = cpu_func(self.result, self.niters)

class IoThread(threading.Thread):
    def __init__(self, sleep):
        super().__init__()
        self.sleep = sleep
        self.result = self.sleep
    def run(self):
        time.sleep(self.sleep)

class IoProcess(multiprocessing.Process):
    def __init__(self, sleep):
        super().__init__()
        self.sleep = sleep
        self.result = self.sleep
    def run(self):
        time.sleep(self.sleep)

if __name__ == '__main__':
    cpu_n_iters = int(sys.argv[1])
    sleep = 1
    cpu_count = multiprocessing.cpu_count()
    input_params = [
        (CpuThread, cpu_n_iters),
        (CpuProcess, cpu_n_iters),
        (IoThread, sleep),
        (IoProcess, sleep),
    ]
    header = ['nthreads']
    for thread_class, _ in input_params:
        header.append(thread_class.__name__)
    print(' '.join(header))
    for nthreads in range(1, 2 * cpu_count):
        results = [nthreads]
        for thread_class, work_size in input_params:
            start_time = time.time()
            threads = []
            for i in range(nthreads):
                thread = thread_class(work_size)
                threads.append(thread)
                thread.start()
            for i, thread in enumerate(threads):
                thread.join()
            results.append(time.time() - start_time)
        print(' '.join('{:.6e}'.format(result) for result in results))

GitHub upstream + plotting code on same directory.

Tested on Ubuntu 18.10, Python 3.6.7, in a Lenovo ThinkPad P51 laptop with CPU: Intel Core i7-7820HQ CPU (4 cores / 8 threads), RAM: 2x Samsung M471A2K43BB1-CRC (2x 16GiB), SSD: Samsung MZVLB512HAJQ-000L7 (3,000 MB/s).

Visualize which threads are running at a given time

This post https://rohanvarma.me/GIL/ taught me that you can run a callback whenever a thread is scheduled with the target= argument of threading.Thread and the same for multiprocessing.Process.

This allows us to view exactly which thread runs at each time. When this is done, we would see something like (I made this particular graph up):

            +--------------------------------------+
            + Active threads / processes           +
+-----------+--------------------------------------+
|Thread   1 |********     ************             |
|         2 |        *****            *************|
+-----------+--------------------------------------+
|Process  1 |***  ************** ******  ****      |
|         2 |** **** ****** ** ********* **********|
+-----------+--------------------------------------+
            + Time -->                             +
            +--------------------------------------+

which would show that:

  • threads are fully serialized by the GIL
  • processes can run in parallel

invalid conversion from 'const char*' to 'char*'

string::c.str() returns a string of type const char * as seen here

A quick fix: try casting printfunc(num,addr,(char *)data.str().c_str());

While the above may work, it is undefined behaviour, and unsafe.

Here's a nicer solution using templates:

char * my_argument = const_cast<char*> ( ...c_str() );

Reading data from XML

I don't think you can "legally" load only part of an XML file, since then it would be malformed (there would be a missing closing element somewhere).

Using LINQ-to-XML, you can do var doc = XDocument.Load("yourfilepath"). From there its just a matter of querying the data you want, say like this:

var authors = doc.Root.Elements().Select( x => x.Element("Author") );

HTH.

EDIT:

Okay, just to make this a better sample, try this (with @JWL_'s suggested improvement):

using System;
using System.Xml.Linq;

namespace ConsoleApplication1 {
    class Program {
        static void Main( string[] args )  {
            XDocument doc = XDocument.Load( "XMLFile1.xml" );
            var authors = doc.Descendants( "Author" );
            foreach ( var author in authors ) {
                Console.WriteLine( author.Value );
            }
            Console.ReadLine();
        }
    }
}

You will need to adjust the path in XDocument.Load() to point to your XML file, but the rest should work. Ask questions about which parts you don't understand.

Access a global variable in a PHP function

It's a matter of scope. In short, global variables should be avoided so:

You either need to pass it as a parameter:

$data = 'My data';

function menugen($data)
{
    echo $data;
}

Or have it in a class and access it

class MyClass
{
    private $data = "";

    function menugen()
    {
        echo this->data;
    }

}

See @MatteoTassinari answer as well, as you can mark it as global to access it, but global variables are generally not required, so it would be wise to re-think your coding.

How can I reduce the waiting (ttfb) time

If you are using PHP, try using <?php flush(); ?> after </head> and before </body> or whatever section you want to output quickly (like the header or content). It will output the actually code without waiting for php to end. Don't use this function all the time, or the speed increase won't be noticable.

More info

Increasing nesting function calls limit

Personally I would suggest this is an error as opposed to a setting that needs adjusting. In my code it was because I had a class that had the same name as a library within one of my controllers and it seemed to trip it up.

Output errors and see where this is being triggered.

size of struct in C

As mentioned, the C compiler will add padding for alignment requirements. These requirements often have to do with the memory subsystem. Some types of computers can only access memory lined up to some 'nice' value, like 4 bytes. This is often the same as the word length. Thus, the C compiler may align fields in your structure to this value to make them easier to access (e.g., 4 byte values should be 4 byte aligned) Further, it may pad the bottom of the structure to line up data which follows the structure. I believe there are other reasons as well. More info can be found at this wikipedia page.

Jquery mouseenter() vs mouseover()

Though they operate the same way, however, the mouseenter event only triggers when the mouse pointer enters the selected element. The mouseover event is triggered if a mouse pointer enters any child elements as well.

How can I check if a user is logged-in in php?

See this script for registering. It is simple and very easy to understand.

<?php
    define('DB_HOST', 'Your Host[Could be localhost or also a website]');
    define('DB_NAME', 'database name');
    define('DB_USERNAME', 'Username[In many cases root, but some sites offer a MySQL page where the username might be different]');
    define('DB_PASSWORD', 'whatever you keep[if username is root then 99% of the password is blank]');

    $link = mysql_connect(DB_HOST, DB_USERNAME, DB_PASSWORD);

    if (!$link) {
        die('Could not connect line 9');
    }

    $DB_SELECT = mysql_select_db(DB_NAME, $link);

    if (!$DB_SELECT) {
        die('Could not connect line 15');
    }

    $valueone = $_POST['name'];
    $valuetwo = $_POST['last_name'];
    $valuethree = $_POST['email'];
    $valuefour = $_POST['password'];
    $valuefive = $_POST['age'];

    $sqlone = "INSERT INTO user (name, last_name, email, password, age) VALUES ('$valueone','$valuetwo','$valuethree','$valuefour','$valuefive')";

    if (!mysql_query($sqlone)) {
        die('Could not connect name line 33');
    }

    mysql_close();
?>

Make sure you make all the database stuff using phpMyAdmin. It's a very easy tool to work with. You can find it here: phpMyAdmin

APK signing error : Failed to read key from keystore

It could be any one of the parameter, not just the file name or alias - for me it was the Key Password.

Rails - How to use a Helper Inside a Controller

In Rails 5+ you can simply use the function as demonstrated below with simple example:

module ApplicationHelper
  # format datetime in the format #2018-12-01 12:12 PM
  def datetime_format(datetime = nil)
    if datetime
      datetime.strftime('%Y-%m-%d %H:%M %p')
    else
      'NA'
    end
  end
end

class ExamplesController < ApplicationController
  def index
    current_datetime = helpers.datetime_format DateTime.now
    raise current_datetime.inspect
  end
end

OUTPUT

"2018-12-10 01:01 AM"

reactjs - how to set inline style of backgroundcolor?

https://facebook.github.io/react/tips/inline-styles.html

You don't need the quotes.

<a style={{backgroundColor: bgColors.Yellow}}>yellow</a>

Numpy: Divide each row by a vector element

Adding to the answer of stackoverflowuser2010, in the general case you can just use

data = np.array([[1,1,1],[2,2,2],[3,3,3]])

vector = np.array([1,2,3])

data / vector.reshape(-1,1)

This will turn your vector into a column matrix/vector. Allowing you to do the elementwise operations as you wish. At least to me, this is the most intuitive way going about it and since (in most cases) numpy will just use a view of the same internal memory for the reshaping it's efficient too.

How can I check if an element exists in the visible DOM?

Check if the element is a child of <html> via Node::contains():

const div = document.createElement('div');
document.documentElement.contains(div); //-> false

document.body.appendChild(div);
document.documentElement.contains(div); //-> true

I've covered this and more in is-dom-detached.

What is the best way to find the users home directory in Java?

The bug you reference (bug 4787391) has been fixed in Java 8. Even if you are using an older version of Java, the System.getProperty("user.home") approach is probably still the best. The user.home approach seems to work in a very large number of cases. A 100% bulletproof solution on Windows is hard, because Windows has a shifting concept of what the home directory means.

If user.home isn't good enough for you I would suggest choosing a definition of home directory for windows and using it, getting the appropriate environment variable with System.getenv(String).

How to display list items as columns?

This can be done using CSS3 columns quite easily. Here's an example, HTML:

_x000D_
_x000D_
#limheight {_x000D_
    height: 300px; /*your fixed height*/_x000D_
    -webkit-column-count: 3;_x000D_
       -moz-column-count: 3;_x000D_
            column-count: 3; /*3 in those rules is just placeholder -- can be anything*/_x000D_
}_x000D_
_x000D_
#limheight li {_x000D_
    display: inline-block; /*necessary*/_x000D_
}
_x000D_
<ul id = "limheight">_x000D_
 <li><a href="">Glee is awesome 1</a></li>_x000D_
 <li><a href="">Glee is awesome 2</a></li>_x000D_
 <li><a href="">Glee is awesome 3</a></li>_x000D_
 <li><a href="">Glee is awesome 4</a></li>    _x000D_
 <li><a href="">Glee is awesome 5</a></li>_x000D_
 <li><a href="">Glee is awesome 6</a></li>_x000D_
 <li><a href="">Glee is awesome 7</a></li>_x000D_
 <li><a href="">Glee is awesome 8</a></li>_x000D_
 <li><a href="">Glee is awesome 9</a></li>_x000D_
 <li><a href="">Glee is awesome 10</a></li>_x000D_
 <li><a href="">Glee is awesome 11</a></li>_x000D_
 <li><a href="">Glee is awesome 12</a></li>    _x000D_
 <li><a href="">Glee is awesome 13</a></li>_x000D_
 <li><a href="">Glee is awesome 14</a></li>_x000D_
 <li><a href="">Glee is awesome 15</a></li>_x000D_
 <li><a href="">Glee is awesome 16</a></li>_x000D_
 <li><a href="">Glee is awesome 17</a></li>    _x000D_
 <li><a href="">Glee is awesome 18</a></li>_x000D_
 <li><a href="">Glee is awesome 19</a></li>_x000D_
 <li><a href="">Glee is awesome 20</a></li>_x000D_
</ul>
_x000D_
_x000D_
_x000D_

Writing to a file in a for loop

That is because you are opening , writing and closing the file 10 times inside your for loop

myfile = open('xyz.txt', 'w')
myfile.writelines(var1)
myfile.close()

You should open and close your file outside for loop.

myfile = open('xyz.txt', 'w')
for line in lines:
    var1, var2 = line.split(",");
    myfile.write("%s\n" % var1)

myfile.close()
text_file.close()

You should also notice to use write and not writelines.

writelines writes a list of lines to your file.

Also you should check out the answers posted by folks here that uses with statement. That is the elegant way to do file read/write operations in Python

What does <meta http-equiv="X-UA-Compatible" content="IE=edge"> do?

Since I can not add a comment to the marked answer I will just post this here.

In addition to the correct answer you can indeed have this validated. Since this meta tag is only directed for IE all you need to do is add a IE conditional.

<!--[if IE]>
    <meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">
<![endif]-->

Doing this is just like adding any other IE conditional statement and only works for IE and no other browsers will be affected.

How to add spacing between columns?

You can achieve spacing between columns using the col-md-offset-* classes, documented here. The spacing is consistent so that all of your columns line up correctly. To get even spacing and column size I would do the following:

<div class="row">
  <div class="col-md-5"></div>
  <div class="col-md-5 col-md-offset-2"></div>
</div>

In Bootstrap 4 use: offset-2 or offset-md-2

How to give a pattern for new line in grep?

You can use this way...

grep -P '^\s$' file
  • -P is used for Perl regular expressions (an extension to POSIX grep).
  • \s match the white space characters; if followed by *, it matches an empty line also.
  • ^ matches the beginning of the line. $ matches the end of the line.

How to stop and restart memcached server?

If you're using homebrew:

brew services restart memcached

How to solve "The specified service has been marked for deletion" error

Sometimes this could happen during service deletion via PowerShell remote session script, especially when you are trying to delete service several times. In this case, try to recreate a session before the deletion:

Remove-PSSession -Session $session
$newSession = New-PSSession -ComputerName $Name  -Credential $creds -ErrorAction Stop
Enter-PSSession $newSession

How to parse a query string into a NameValueCollection in .NET

There's a built-in .NET utility for this: HttpUtility.ParseQueryString

// C#
NameValueCollection qscoll = HttpUtility.ParseQueryString(querystring);
' VB.NET
Dim qscoll As NameValueCollection = HttpUtility.ParseQueryString(querystring)

You may need to replace querystring with new Uri(fullUrl).Query.

Is there a method that calculates a factorial in Java?

Factorial is highly increasing discrete function.So I think using BigInteger is better than using int. I have implemented following code for calculation of factorial of non-negative integers.I have used recursion in place of using a loop.

public  BigInteger factorial(BigInteger x){     
    if(x.compareTo(new BigInteger("1"))==0||x.compareTo(new BigInteger("0"))==0)
        return new BigInteger("1");
    else return x.multiply(factorial(x.subtract(new BigInteger("1")))); 
}

Here the range of big integer is

-2^Integer.MAX_VALUE (exclusive) to +2^Integer.MAX_VALUE,
where Integer.MAX_VALUE=2^31.

However the range of the factorial method given above can be extended up to twice by using unsigned BigInteger.

Clearing _POST array fully

It may appear to be overly awkward, but you're probably better off unsetting one element at a time rather than the entire $_POST array. Here's why: If you're using object-oriented programming, you may have one class use $_POST['alpha'] and another class use $_POST['beta'], and if you unset the array after first use, it will void its use in other classes. To be safe and not shoot yourself in the foot, just drop in a little method that will unset the elements that you've just used: For example:

private function doUnset()
{
    unset($_POST['alpha']);
    unset($_POST['gamma']);
    unset($_POST['delta']);
    unset($_GET['eta']);
    unset($_GET['zeta']);
}

Just call the method and unset just those superglobal elements that have been passed to a variable or argument. Then, the other classes that may need a superglobal element can still use them.

However, you are wise to unset the superglobals as soon as they have been passed to an encapsulated object.

How do I write dispatch_after GCD in Swift 3, 4, and 5?

call DispatchQueue.main.after(when: DispatchTime, execute: () -> Void)

I'd highly recommend using the Xcode tools to convert to Swift 3 (Edit > Convert > To Current Swift Syntax). It caught this for me

How to rename a file using Python

File may be inside a directory, in that case specify the path:

import os
old_file = os.path.join("directory", "a.txt")
new_file = os.path.join("directory", "b.kml")
os.rename(old_file, new_file)

Open Windows Explorer and select a file

Check out this snippet:

Private Sub openDialog()
    Dim fd As Office.FileDialog

    Set fd = Application.FileDialog(msoFileDialogFilePicker)

   With fd

      .AllowMultiSelect = False

      ' Set the title of the dialog box.
      .Title = "Please select the file."

      ' Clear out the current filters, and add our own.
      .Filters.Clear
      .Filters.Add "Excel 2003", "*.xls"
      .Filters.Add "All Files", "*.*"

      ' Show the dialog box. If the .Show method returns True, the
      ' user picked at least one file. If the .Show method returns
      ' False, the user clicked Cancel.
      If .Show = True Then
        txtFileName = .SelectedItems(1) 'replace txtFileName with your textbox

      End If
   End With
End Sub

I think this is what you are asking for.

SQL Server Creating a temp table for this query

If you want to just create a temp table inside the query that will allow you to do something with the results that you deposit into it you can do something like the following:

DECLARE @T1 TABLE (
Item 1 VARCHAR(200)
, Item 2 VARCHAR(200)
, ...
, Item n VARCHAR(500)
)

On the top of your query and then do an

INSERT INTO @T1
SELECT
FROM
(...)

Can you change what a symlink points to after it is created?

It is not necessary to explicitly unlink the old symlink. You can do this:

ln -s newtarget temp
mv temp mylink

(or use the equivalent symlink and rename calls). This is better than explicitly unlinking because rename is atomic, so you can be assured that the link will always point to either the old or new target. However this will not reuse the original inode.

On some filesystems, the target of the symlink is stored in the inode itself (in place of the block list) if it is short enough; this is determined at the time it is created.

Regarding the assertion that the actual owner and group are immaterial, symlink(7) on Linux says that there is a case where it is significant:

The owner and group of an existing symbolic link can be changed using lchown(2). The only time that the ownership of a symbolic link matters is when the link is being removed or renamed in a directory that has the sticky bit set (see stat(2)).

The last access and last modification timestamps of a symbolic link can be changed using utimensat(2) or lutimes(3).

On Linux, the permissions of a symbolic link are not used in any operations; the permissions are always 0777 (read, write, and execute for all user categories), and can't be changed.

Obtaining only the filename when using OpenFileDialog property "FileName"

Use OpenFileDialog.SafeFileName

OpenFileDialog.SafeFileName Gets the file name and extension for the file selected in the dialog box. The file name does not include the path.

How to connect to Mysql Server inside VirtualBox Vagrant?

Make sure MySQL binds to 0.0.0.0 and not 127.0.0.1 or it will not be accessible from outside the machine

You can ensure this by editing your my.conf file and looking for the bind-address item--you want it to look like bind-address = 0.0.0.0. Then save this and restart mysql:

sudo service mysql restart

If you are doing this on a production server, you want to be aware of the security implications, discussed here: https://serverfault.com/questions/257513/how-bad-is-setting-mysqls-bind-address-to-0-0-0-0

Excel CSV - Number cell format

Load csv into oleDB and force all inferred datatypes to string

i asked the same question and then answerd it with code.

basically when the csv file is loaded the oledb driver makes assumptions, you can tell it what assumptions to make.

My code forces all datatypes to string though ... its very easy to change the schema. for my purposes i used an xslt to get ti the way i wanted - but i am parsing a wide variety of files.

Search in all files in a project in Sublime Text 3

You can put <project> in "Where:" box to search from the current Sublime project from the Find in Files menu.

This is more useful than searching from the root folder for when your project is including or excluding particular folders or file extensions.

Java HashMap performance optimization / alternative

If the arrays in your posted hashCode are bytes, then you will likely end up with lots of duplicates.

a[0] + a[1] will always be between 0 and 512. adding the b's will always result in a number between 0 and 768. multiply those and you get an upper limit of 400,000 unique combinations, assuming your data is perfectly distributed among every possible value of each byte. If your data is at all regular, you likely have far less unique outputs of this method.

Best way to do nested case statement logic in SQL Server

I personally do it this way, keeping the embedded CASE expressions confined. I'd also put comments in to explain what is going on. If it is too complex, break it out into function.

SELECT
    col1,
    col2,
    col3,
    CASE WHEN condition THEN
      CASE WHEN condition1 THEN
        CASE WHEN condition2 THEN calculation1
        ELSE calculation2 END
      ELSE
        CASE WHEN condition2 THEN calculation3
        ELSE calculation4 END
      END
    ELSE CASE WHEN condition1 THEN 
      CASE WHEN condition2 THEN calculation5
      ELSE calculation6 END
    ELSE CASE WHEN condition2 THEN calculation7
         ELSE calculation8 END
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

Running multiple commands with xargs

Another possible solution that works for me is something like -

cat a.txt | xargs bash -c 'command1 $@; command2 $@' bash

Note the 'bash' at the end - I assume it is passed as argv[0] to bash. Without it in this syntax the first parameter to each command is lost. It may be any word.

Example:

cat a.txt | xargs -n 5 bash -c 'echo -n `date +%Y%m%d-%H%M%S:` ; echo " data: " $@; echo "data again: " $@' bash

How do you reinstall an app's dependencies using npm?

You can do this with one simple command:

npm ci

Documentation:

npm ci
Install a project with a clean slate

How do I execute code AFTER a form has loaded?

You could use the "Shown" event: MSDN - Form.Shown

"The Shown event is only raised the first time a form is displayed; subsequently minimizing, maximizing, restoring, hiding, showing, or invalidating and repainting will not raise this event."

How to add a delay for a 2 or 3 seconds

You could use Thread.Sleep() function, e.g.

int milliseconds = 2000;
Thread.Sleep(milliseconds);

that completely stops the execution of the current thread for 2 seconds.

Probably the most appropriate scenario for Thread.Sleep is when you want to delay the operations in another thread, different from the main e.g. :

 MAIN THREAD        --------------------------------------------------------->
 (UI, CONSOLE ETC.)      |                                      |
                         |                                      |
 OTHER THREAD            ----- ADD A DELAY (Thread.Sleep) ------>

For other scenarios (e.g. starting operations after some time etc.) check Cody's answer.

What is the difference between const int*, const int * const, and int const *?

For those who don't know about Clockwise/Spiral Rule: Start from the name of the variable, move clockwisely (in this case, move backward) to the next pointer or type. Repeat until expression ends.

Here is a demo:

pointer to int

const pointer to int const

pointer to int const

pointer to const int

const pointer to int

Error: JavaFX runtime components are missing, and are required to run this application with JDK 11

This worked for me:

File >> Project Structure >> Modules >> Dependency >> + (on left-side of window)

clicking the "+" sign will let you designate the directory where you have unpacked JavaFX's "lib" folder.

Scope is Compile (which is the default.) You can then edit this to call it JavaFX by double-clicking on the line.

then in:

Run >> Edit Configurations

Add this line to VM Options:

--module-path /path/to/JavaFX/lib --add-modules=javafx.controls

(oh and don't forget to set the SDK)

String isNullOrEmpty in Java?

from Apache commons-lang.

The difference between empty and blank is : a string consisted of whitespaces only is blank but isn't empty.

I generally prefer using apache-commons if possible, instead of writing my own utility methods, although that is also plausible for simple ones like these.

How to use if statements in underscore.js templates?

To check for null values you could use _.isNull from official documentation

isNull_.isNull(object)

Returns true if the value of object is null.

_.isNull(null);
=> true
_.isNull(undefined);
=> false

Call a Javascript function every 5 seconds continuously

Do a "recursive" setTimeout of your function, and it will keep being executed every amount of time defined:

function yourFunction(){
    // do whatever you like here

    setTimeout(yourFunction, 5000);
}

yourFunction();

Creating runnable JAR with Gradle

As others have noted, in order for a jar file to be executable, the application's entry point must be set in the Main-Class attribute of the manifest file. If the dependency class files are not collocated, then they need to be set in the Class-Path entry of the manifest file.

I have tried all kinds of plugin combinations and what not for the simple task of creating an executable jar and somehow someway, include the dependencies. All plugins seem to be lacking one way or another, but finally I got it like I wanted. No mysterious scripts, not a million different mini files polluting the build directory, a pretty clean build script file, and above all: not a million foreign third party class files merged into my jar archive.

The following is a copy-paste from here for your convenience..

[How-to] create a distribution zip file with dependency jars in subdirectory /lib and add all dependencies to Class-Path entry in the manifest file:

apply plugin: 'java'
apply plugin: 'java-library-distribution'

repositories {
    mavenCentral()
}

dependencies {
    compile 'org.apache.commons:commons-lang3:3.3.2'
}

// Task "distZip" added by plugin "java-library-distribution":
distZip.shouldRunAfter(build)

jar {
    // Keep jar clean:
    exclude 'META-INF/*.SF', 'META-INF/*.DSA', 'META-INF/*.RSA', 'META-INF/*.MF'

    manifest {
        attributes 'Main-Class': 'com.somepackage.MainClass',
                   'Class-Path': configurations.runtime.files.collect { "lib/$it.name" }.join(' ')
    }
    // How-to add class path:
    //     https://stackoverflow.com/questions/22659463/add-classpath-in-manifest-using-gradle
    //     https://gist.github.com/simon04/6865179
}

Hosted as a gist here.

The result can be found in build/distributions and the unzipped contents look like this:

lib/commons-lang3-3.3.2.jar
MyJarFile.jar

Contents of MyJarFile.jar#META-INF/MANIFEST.mf:

Manifest-Version: 1.0
Main-Class: com.somepackage.MainClass
Class-Path: lib/commons-lang3-3.3.2.jar

Identify if a string is a number

I've used this function several times:

public static bool IsNumeric(object Expression)
{
    double retNum;

    bool isNum = Double.TryParse(Convert.ToString(Expression), System.Globalization.NumberStyles.Any, System.Globalization.NumberFormatInfo.InvariantInfo, out retNum);
    return isNum;
}

But you can also use;

bool b1 = Microsoft.VisualBasic.Information.IsNumeric("1"); //true
bool b2 = Microsoft.VisualBasic.Information.IsNumeric("1aa"); // false

From Benchmarking IsNumeric Options

alt text
(source: aspalliance.com)

alt text
(source: aspalliance.com)

How do I create and access the global variables in Groovy?

class Globals {
   static String ouch = "I'm global.."
}

println Globals.ouch

Appending a line to a file only if it does not already exist

If, one day, someone else have to deal with this code as "legacy code", then that person will be grateful if you write a less exoteric code, such as

grep -q -F 'include "/configs/projectname.conf"' lighttpd.conf
if [ $? -ne 0 ]; then
  echo 'include "/configs/projectname.conf"' >> lighttpd.conf
fi

sendUserActionEvent() is null

Even i face similar problem after I did some modification in code related to Cursor.

public boolean onContextItemSelected(MenuItem item) 
{
        AdapterContextMenuInfo info = (AdapterContextMenuInfo)item.getMenuInfo();
        Cursor c = (Cursor)adapter.getItem(info.position);
        long id = c.getLong(...);
        String tempCity = c.getString(...);
            //c.close();
...
}

After i commented out //c.close(); It is working fine. Try out at your end and update Initial setup is as... I have a list view in Fragment, and trying to delete and item from list via contextMenu.

How can I use jQuery to make an input readonly?

You can do this by simply marking it disabled or enabled. You can use this code to do this:

//for disable
$('#fieldName').prop('disabled', true);

//for enable 
$('#fieldName').prop('disabled', false);

or

$('#fieldName').prop('readonly', true);

$('#fieldName').prop('readonly', false);

--- Its better to use prop instead of attr.

Iterate through a C array

It depends. If it's a dynamically allocated array, that is, you created it calling malloc, then as others suggest you must either save the size of the array/number of elements somewhere or have a sentinel (a struct with a special value, that will be the last one).

If it's a static array, you can sizeof it's size/the size of one element. For example:

int array[10], array_size;
...
array_size = sizeof(array)/sizeof(int);

Note that, unless it's global, this only works in the scope where you initialized the array, because if you past it to another function it gets decayed to a pointer.

Hope it helps.

How to match hyphens with Regular Expression?

Is this what you are after?

MatchCollection matches = Regex.Matches(mystring, "-");

Install opencv for Python 3.3

You can use the following command on the command prompt (cmd) on Windows:

py -3.3 -m pip install opencv-python

I made a video on how to install OpenCV Python on Windows in 1 minute here:

https://www.youtube.com/watch?v=m2-8SHk-1SM

Hope it helps!

How do I center a Bootstrap div with a 'spanX' class?

Incidentally, if your span class is even-numbered (e.g. span8) you can add an offset class to center it – for span8 that would be offset2 (assuming the default 12-column grid), for span6 it would be offset3 and so on (basically, half the number of remaining columns if you subtract the span-number from the total number of columns in the grid).

UPDATE Bootstrap 3 renamed a lot of classes so all the span*classes should be col-md-* and the offset classes should be col-md-offset-*, assuming you're using the medium-sized responsive grid.

I created a quick demo here, hope it helps: http://codepen.io/anon/pen/BEyHd.

PHP $_SERVER['HTTP_HOST'] vs. $_SERVER['SERVER_NAME'], am I understanding the man pages correctly?

This is a verbose translation of what Symfony uses to get the host name (see the second example for a more literal translation):

function getHost() {
    $possibleHostSources = array('HTTP_X_FORWARDED_HOST', 'HTTP_HOST', 'SERVER_NAME', 'SERVER_ADDR');
    $sourceTransformations = array(
        "HTTP_X_FORWARDED_HOST" => function($value) {
            $elements = explode(',', $value);
            return trim(end($elements));
        }
    );
    $host = '';
    foreach ($possibleHostSources as $source)
    {
        if (!empty($host)) break;
        if (empty($_SERVER[$source])) continue;
        $host = $_SERVER[$source];
        if (array_key_exists($source, $sourceTransformations))
        {
            $host = $sourceTransformations[$source]($host);
        } 
    }

    // Remove port number from host
    $host = preg_replace('/:\d+$/', '', $host);

    return trim($host);
}

Outdated:

This is my translation to bare PHP of a method used in Symfony framework that tries to get the hostname from every way possible in order of best practice:

function get_host() {
    if ($host = $_SERVER['HTTP_X_FORWARDED_HOST'])
    {
        $elements = explode(',', $host);

        $host = trim(end($elements));
    }
    else
    {
        if (!$host = $_SERVER['HTTP_HOST'])
        {
            if (!$host = $_SERVER['SERVER_NAME'])
            {
                $host = !empty($_SERVER['SERVER_ADDR']) ? $_SERVER['SERVER_ADDR'] : '';
            }
        }
    }

    // Remove port number from host
    $host = preg_replace('/:\d+$/', '', $host);

    return trim($host);
}

What is a tracking branch?

The Pro Git book mentions:

Tracking branches are local branches that have a direct relationship to a remote branch

Not exactly. The SO question "Having a hard time understanding git-fetch" includes:

There's no such concept of local tracking branches, only remote tracking branches.
So origin/master is a remote tracking branch for master in the origin repo.

But actually, once you establish an upstream branch relationship between:

  • a local branch like master
  • and a remote tracking branch like origin/master

Then you can consider master as a local tracking branch: It tracks the remote tracking branch origin/master which, in turn, tracks the master branch of the upstream repo origin.

alt text

How to move text up using CSS when nothing is working

you can try

position: relative;
bottom: 20px;

but I don't see a problem on my browser (Google Chrome)

How to find the most recent file in a directory using .NET, and without looping?

A non-LINQ version:

/// <summary>
/// Returns latest writen file from the specified directory.
/// If the directory does not exist or doesn't contain any file, DateTime.MinValue is returned.
/// </summary>
/// <param name="directoryInfo">Path of the directory that needs to be scanned</param>
/// <returns></returns>
private static DateTime GetLatestWriteTimeFromFileInDirectory(DirectoryInfo directoryInfo)
{
    if (directoryInfo == null || !directoryInfo.Exists)
        return DateTime.MinValue;

    FileInfo[] files = directoryInfo.GetFiles();
    DateTime lastWrite = DateTime.MinValue;

    foreach (FileInfo file in files)
    {
        if (file.LastWriteTime > lastWrite)
        {
            lastWrite = file.LastWriteTime;
        }
    }

    return lastWrite;
}

/// <summary>
/// Returns file's latest writen timestamp from the specified directory.
/// If the directory does not exist or doesn't contain any file, null is returned.
/// </summary>
/// <param name="directoryInfo">Path of the directory that needs to be scanned</param>
/// <returns></returns>
private static FileInfo GetLatestWritenFileFileInDirectory(DirectoryInfo directoryInfo)
{
    if (directoryInfo == null || !directoryInfo.Exists)
        return null;

    FileInfo[] files = directoryInfo.GetFiles();
    DateTime lastWrite = DateTime.MinValue;
    FileInfo lastWritenFile = null;

    foreach (FileInfo file in files)
    {
        if (file.LastWriteTime > lastWrite)
        {
            lastWrite = file.LastWriteTime;
            lastWritenFile = file;
        }
    }
    return lastWritenFile;
}

How do I read any request header in PHP

I was using CodeIgniter and used the code below to get it. May be useful for someone in future.

$this->input->get_request_header('X-Requested-With');

How to diff a commit with its parent?

If you know how far back, you can try something like:

# Current branch vs. parent
git diff HEAD^ HEAD

# Current branch, diff between commits 2 and 3 times back
git diff HEAD~3 HEAD~2

Prior commits work something like this:

# Parent of HEAD
git show HEAD^1

# Grandparent
git show HEAD^2

There are a lot of ways you can specify commits:

# Great grandparent
git show HEAD~3

See this page for details.

Cleanest Way to Invoke Cross-Thread Events

Use the synchronisation context if you want to send a result to the UI thread. I needed to change the thread priority so I changed from using thread pool threads (commented out code) and created a new thread of my own. I was still able to use the synchronisation context to return whether the database cancel succeeded or not.

    #region SyncContextCancel

    private SynchronizationContext _syncContextCancel;

    /// <summary>
    /// Gets the synchronization context used for UI-related operations.
    /// </summary>
    /// <value>The synchronization context.</value>
    protected SynchronizationContext SyncContextCancel
    {
        get { return _syncContextCancel; }
    }

    #endregion //SyncContextCancel

    public void CancelCurrentDbCommand()
    {
        _syncContextCancel = SynchronizationContext.Current;

        //ThreadPool.QueueUserWorkItem(CancelWork, null);

        Thread worker = new Thread(new ThreadStart(CancelWork));
        worker.Priority = ThreadPriority.Highest;
        worker.Start();
    }

    SQLiteConnection _connection;
    private void CancelWork()//object state
    {
        bool success = false;

        try
        {
            if (_connection != null)
            {
                log.Debug("call cancel");
                _connection.Cancel();
                log.Debug("cancel complete");
                _connection.Close();
                log.Debug("close complete");
                success = true;
                log.Debug("long running query cancelled" + DateTime.Now.ToLongTimeString());
            }
        }
        catch (Exception ex)
        {
            log.Error(ex.Message, ex);
        }

        SyncContextCancel.Send(CancelCompleted, new object[] { success });
    }

    public void CancelCompleted(object state)
    {
        object[] args = (object[])state;
        bool success = (bool)args[0];

        if (success)
        {
            log.Debug("long running query cancelled" + DateTime.Now.ToLongTimeString());

        }
    }

Plugin org.apache.maven.plugins:maven-clean-plugin:2.5 or one of its dependencies could not be resolved

I resolved this issue by switching to the oracle jdk from open jdk 8.

$ java -version java version "1.8.0_221" Java(TM) SE Runtime Environment (build 1.8.0_221-b11) Java HotSpot(TM) 64-Bit Server VM (build 25.221-b11, mixed mode)

shell init issue when click tab, what's wrong with getcwd?

This usually occurs when your current directory does not exist anymore. Most likely, from another terminal you remove that directory (from within a script or whatever). To get rid of this, in case your current directory was recreated in the meantime, just cd to another (existing) directory and then cd back; the simplest would be: cd; cd -.

Angular 4 - Observable catch error

You should be using below

return Observable.throw(error || 'Internal Server error');

Import the throw operator using the below line

import 'rxjs/add/observable/throw';

C# elegant way to check if a property's property is null

Just stumbled accross this post.

Some time ago I made a suggestion on Visual Studio Connect about adding a new ??? operator.

http://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/4104392-add-as-an-recursive-null-reference-check-opera

This would require some work from the framework team but don't need to alter the language but just do some compiler magic. The idea was that the compiler should change this code (syntax not allowed atm)

string product_name = Order.OrderDetails[0].Product.Name ??? "no product defined";

into this code

Func<string> _get_default = () => "no product defined"; 
string product_name = Order == null 
    ? _get_default.Invoke() 
    : Order.OrderDetails[0] == null 
        ? _get_default.Invoke() 
        : Order.OrderDetails[0].Product == null 
            ? _get_default.Invoke() 
            : Order.OrderDetails[0].Product.Name ?? _get_default.Invoke()

For null check this could look like

bool isNull = (Order.OrderDetails[0].Product ??? null) == null;

php - add + 7 days to date format mm dd, YYYY

The "+1 month" issue with strtotime

As noted in several blogs, strtotime() solves the "+1 month" ("next month") issue on days that do not exist in the subsequent month differently than other implementations like for example MySQL.

$dt = date("Y-m-d");
echo date( "Y-m-d", strtotime( "$dt +1 day" ) ); // PHP:  2009-03-04
echo date( "Y-m-d", strtotime( "2009-01-31 +2 month" ) ); // PHP:  2009-03-31

Python Hexadecimal

Use the format() function with a '02x' format.

>>> format(255, '02x')
'ff'
>>> format(2, '02x')
'02'

The 02 part tells format() to use at least 2 digits and to use zeros to pad it to length, x means lower-case hexadecimal.

The Format Specification Mini Language also gives you X for uppercase hex output, and you can prefix the field width with # to include a 0x or 0X prefix (depending on wether you used x or X as the formatter). Just take into account that you need to adjust the field width to allow for those extra 2 characters:

>>> format(255, '02X')
'FF'
>>> format(255, '#04x')
'0xff'
>>> format(255, '#04X')
'0XFF'

Firing a Keyboard Event in Safari, using JavaScript

This is due to a bug in Webkit.

You can work around the Webkit bug using createEvent('Event') rather than createEvent('KeyboardEvent'), and then assigning the keyCode property. See this answer and this example.

Is it possible to set a number to NaN or infinity?

Yes, you can use numpy for that.

import numpy as np
a = arange(3,dtype=float)

a[0] = np.nan
a[1] = np.inf
a[2] = -np.inf

a # is now [nan,inf,-inf]

np.isnan(a[0]) # True
np.isinf(a[1]) # True
np.isinf(a[2]) # True

Java Try and Catch IOException Problem

Your countLines(String filename) method throws IOException.

You can't use it in a member declaration. You'll need to perform the operation in a main(String[] args) method.

Your main(String[] args) method will get the IOException thrown to it by countLines and it will need to handle or declare it.

Try this to just throw the IOException from main

public class MyClass {
  private int lineCount;
  public static void main(String[] args) throws IOException {
    lineCount = LineCounter.countLines(sFileName);
  }
}

or this to handle it and wrap it in an unchecked IllegalArgumentException:

public class MyClass {
  private int lineCount;
  private String sFileName  = "myfile";
  public static void main(String[] args) throws IOException {
    try {
      lineCount = LineCounter.countLines(sFileName);
     } catch (IOException e) {
       throw new IllegalArgumentException("Unable to load " + sFileName, e);
     }
  }
}

LDAP: error code 49 - 80090308: LdapErr: DSID-0C0903A9, comment: AcceptSecurityContext error, data 52e, v1db1

For me the issue is resolved by adding domain name in user name as follow:

string userName="yourUserName";
string password="passowrd";
string hostName="LdapServerHostName";
string domain="yourDomain";
System.DirectoryServices.AuthenticationTypes option = System.DirectoryServices.AuthenticationTypes.SecureSocketsLayer; 
string userNameWithDomain = string.Format("{0}@{1}",userName , domain);
DirectoryEntry directoryOU = new DirectoryEntry("LDAP://" + hostName, userNameWithDomain, password, option);

Using psql to connect to PostgreSQL in SSL mode

psql below 9.2 does not accept this URL-like syntax for options.

The use of SSL can be driven by the sslmode=value option on the command line or the PGSSLMODE environment variable, but the default being prefer, SSL connections will be tried first automatically without specifying anything.

Example with a conninfo string (updated for psql 8.4)

psql "sslmode=require host=localhost dbname=test"

Read the manual page for more options.

How do I convert a number to a numeric, comma-separated formatted string?

You really shouldn't be doing that in SQL - you should be formatting it in the middleware instead. But I recognize that sometimes there is an edge case that requires one to do such a thing.

This looks like it might have your answer:

How do I format a number with commas in T-SQL?

From ND to 1D arrays

Use np.ravel (for a 1D view) or np.ndarray.flatten (for a 1D copy) or np.ndarray.flat (for an 1D iterator):

In [12]: a = np.array([[1,2,3], [4,5,6]])

In [13]: b = a.ravel()

In [14]: b
Out[14]: array([1, 2, 3, 4, 5, 6])

Note that ravel() returns a view of a when possible. So modifying b also modifies a. ravel() returns a view when the 1D elements are contiguous in memory, but would return a copy if, for example, a were made from slicing another array using a non-unit step size (e.g. a = x[::2]).

If you want a copy rather than a view, use

In [15]: c = a.flatten()

If you just want an iterator, use np.ndarray.flat:

In [20]: d = a.flat

In [21]: d
Out[21]: <numpy.flatiter object at 0x8ec2068>

In [22]: list(d)
Out[22]: [1, 2, 3, 4, 5, 6]

How to use not contains() in xpath?

XPath queries are case sensitive. Having looked at your example (which, by the way, is awesome, nobody seems to provide examples anymore!), I can get the result you want just by changing "business", to "Business"

//production[not(contains(category,'Business'))]

I have tested this by opening the XML file in Chrome, and using the Developer tools to execute that XPath queries, and it gave me just the Film category back.

How to execute a .bat file from a C# windows form app?

Here is what you are looking for:

Service hangs up at WaitForExit after calling batch file

It's about a question as to why a service can't execute a file, but it shows all the code necessary to do so.

Pretty-print an entire Pandas Series / DataFrame

Using pd.options.display

This answer is a variation of the prior answer by lucidyan. It makes the code more readable by avoiding the use of set_option.

After importing pandas, as an alternative to using the context manager, set such options for displaying large dataframes:

def set_pandas_display_options() -> None:
    """Set pandas display options."""
    # Ref: https://stackoverflow.com/a/52432757/
    display = pd.options.display

    display.max_columns = 1000
    display.max_rows = 1000
    display.max_colwidth = 199
    display.width = None
    # display.precision = 2  # set as needed

set_pandas_display_options()

After this, you can use either display(df) or just df if using a notebook, otherwise print(df).

Using to_string

Pandas 0.25.3 does have DataFrame.to_string and Series.to_string methods which accept formatting options.

Using to_markdown

If what you need is markdown output, Pandas 1.0.0 has DataFrame.to_markdown and Series.to_markdown methods.

Using to_html

If what you need is HTML output, Pandas 0.25.3 does have a DataFrame.to_html method but not a Series.to_html. Note that a Series can be converted to a DataFrame.

How to find tag with particular text with Beautiful Soup?

You can pass a regular expression to the text parameter of findAll, like so:

import BeautifulSoup
import re

columns = soup.findAll('td', text = re.compile('your regex here'), attrs = {'class' : 'pos'})

How to correctly save instance state of Fragments in back stack?

On the latest support library none of the solutions discussed here are necessary anymore. You can play with your Activity's fragments as you like using the FragmentTransaction. Just make sure that your fragments can be identified either with an id or tag.

The fragments will be restored automatically as long as you don't try to recreate them on every call to onCreate(). Instead, you should check if savedInstanceState is not null and find the old references to the created fragments in this case.

Here is an example:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    if (savedInstanceState == null) {
        myFragment = MyFragment.newInstance();
        getSupportFragmentManager()
                .beginTransaction()
                .add(R.id.my_container, myFragment, MY_FRAGMENT_TAG)
                .commit();
    } else {
        myFragment = (MyFragment) getSupportFragmentManager()
                .findFragmentByTag(MY_FRAGMENT_TAG);
    }
...
}

Note however that there is currently a bug when restoring the hidden state of a fragment. If you are hiding fragments in your activity, you will need to restore this state manually in this case.

Trying to get property of non-object - Laravel 5

It happen that after some time we need to run

 'php artisan passport:install --force 

again to generate a key this solved my problem ,

Finding a branch point with Git?

A simple way to just make it easier to see the branching point in git log --graph is to use the option --first-parent.

For example, take the repo from the accepted answer:

$ git log --all --oneline --decorate --graph

*   a9546a2 (HEAD -> master, origin/master, origin/HEAD) merge from topic back to master
|\  
| *   648ca35 (origin/topic) merging master onto topic
| |\  
| * | 132ee2a first commit on topic branch
* | | e7c863d commit on master after master was merged to topic
| |/  
|/|   
* | 37ad159 post-branch commit on master
|/  
* 6aafd7f second commit on master before branching
* 4112403 initial commit on master

Now add --first-parent:

$ git log --all --oneline --decorate --graph --first-parent

* a9546a2 (HEAD -> master, origin/master, origin/HEAD) merge from topic back to master
| * 648ca35 (origin/topic) merging master onto topic
| * 132ee2a first commit on topic branch
* | e7c863d commit on master after master was merged to topic
* | 37ad159 post-branch commit on master
|/  
* 6aafd7f second commit on master before branching
* 4112403 initial commit on master

That makes it easier!

Note if the repo has lots of branches you're going to want to specify the 2 branches you're comparing instead of using --all:

$ git log --decorate --oneline --graph --first-parent master origin/topic

How to vertically align elements in a div?

Use this formula, and it will works always without cracks:

_x000D_
_x000D_
#outer {height: 400px; overflow: hidden; position: relative;}_x000D_
#outer[id] {display: table; position: static;}_x000D_
_x000D_
#middle {position: absolute; top: 50%;} /* For explorer only*/_x000D_
#middle[id] {display: table-cell; vertical-align: middle; width: 100%;}_x000D_
_x000D_
#inner {position: relative; top: -50%} /* For explorer only */_x000D_
/* Optional: #inner[id] {position: static;} */
_x000D_
<div id="outer">_x000D_
  <div id="middle">_x000D_
    <div id="inner">_x000D_
      any text_x000D_
      any height_x000D_
      any content, for example generated from DB_x000D_
      everything is vertically centered_x000D_
    </div>_x000D_
  </div>_x000D_
</div>
_x000D_
_x000D_
_x000D_

random number generator between 0 - 1000 in c#

Use this:

static int RandomNumber(int min, int max)
{
    Random random = new Random(); return random.Next(min, max);

}

This is example for you to modify and use in your application.

jQuery remove special characters from string and more

replace(/[^a-z0-9\s]/gi, '') will filter the string down to just alphanumeric values and replace(/[_\s]/g, '-') will replace underscores and spaces with hyphens:

str.replace(/[^a-z0-9\s]/gi, '').replace(/[_\s]/g, '-')

Source for Regex: RegEx for Javascript to allow only alphanumeric

Here is a demo: http://jsfiddle.net/vNfrk/

Get selected element's outer HTML

jQuery plugin as a shorthand to directly get the whole element HTML:

jQuery.fn.outerHTML = function () {
    return jQuery('<div />').append(this.eq(0).clone()).html();
};

And use it like this: $(".element").outerHTML();

Having Django serve downloadable files

S.Lott has the "good"/simple solution, and elo80ka has the "best"/efficient solution. Here is a "better"/middle solution - no server setup, but more efficient for large files than the naive fix:

http://djangosnippets.org/snippets/365/

Basically, Django still handles serving the file but does not load the whole thing into memory at once. This allows your server to (slowly) serve a big file without ramping up the memory usage.

Again, S.Lott's X-SendFile is still better for larger files. But if you can't or don't want to bother with that, then this middle solution will gain you better efficiency without the hassle.

Two div blocks on same line

Use below Css:

#bloc1,
#bloc2 {
display:inline
} 

body {
text-align:center
}

It will make the mentioned 2 divs in the center on the same line.