Programs & Examples On #Mappers

Hibernate Error executing DDL via JDBC Statement

Another sneaky issue related to this is naming your columns with - instead of _.

Something like this will trigger an error at the moment your tables are getting created.


Container is running beyond memory limits

Running yarn on Windows Linux subsystem with Ubunto OS, error "running beyond virtual memory limits, Killing container" I resolved it by disabling virtual memory check in the file yarn-site.xml

<property> <name>yarn.nodemanager.vmem-check-enabled</name> <value>false</value> </property> 

Change SVN repository URL

Grepping the URL before and after might give you some peace of mind:

svn info | grep URL

  URL: svn://
  Relative URL: (...doesn't matter...)

And checking on your version (to be >1.7) to ensure, svn relocate is the right thing to use:

svn --version

Lastly, adding to the above, if your repository url change also involves a change of protocol you might need to state the before and after url (also see here)

svn relocate svn://

All in one single line of course.Thereafter, get the good feeling, that all went smoothly:

svn info | grep URL:

If you feel like it, a bit more of self-assurance, the new svn repo URL is connected and working:

svn status --show-updates
svn diff

Laravel: Get base url

You can use facades or helper function as per following.

echo URL::to('/');
echo url();

Laravel using Symfony Component for Request, Laravel internal logic as per following.

namespace Symfony\Component\HttpFoundation;
* {@inheritdoc}
protected function prepareBaseUrl()
    $baseUrl = $this->server->get('SCRIPT_NAME');

    if (false === strpos($this->server->get('REQUEST_URI'), $baseUrl)) {
        // assume mod_rewrite
        return rtrim(dirname($baseUrl), '/\\');

    return $baseUrl;

CSS endless rotation animation

Rotation on add class .active {
                -webkit-animation: spin 4s linear infinite;
                -moz-animation: spin 4s linear infinite;
                animation: spin 4s linear infinite;

@-moz-keyframes spin {
       100% {
        -moz-transform: rotate(360deg);
     @-webkit-keyframes spin {
      100% {
         -webkit-transform: rotate(360deg);
     @keyframes spin {
       100% {
         -webkit-transform: rotate(360deg);
         transform: rotate(360deg);

Get docker container id from container name

The simplest way I can think of is to parse the output of docker ps

Let's run the latest ubuntu image interactively and connect to it

docker run -it ubuntu /bin/bash

If you run docker ps in another terminal you can see something like

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
8fddbcbb101c        ubuntu:latest       "/bin/bash"         10 minutes ago      Up 10 minutes                           gloomy_pasteur

Unfortunately, parsing this format isn't easy since they uses spaces to manually align stuff

$ sudo docker ps | sed -e 's/ /@/g'

Here is a script that converts the output to JSON.

Actually, the output is a bit more convenient to work with than that. Every field is 20 characters wide. [['CONTAINER ID',0],['IMAGE',20],['COMMAND',40],['CREATED',60],['STATUS',80],['PORTS',100],['NAMES',120]]

Difference in days between two dates in Java?

It depends on what you define as the difference. To compare two dates at midnight you can do.

long day1 = ...; // in milliseconds.
long day2 = ...; // in milliseconds.
long days = (day2 - day1) / 86400000;

Is this how you define a function in jQuery?

No, you can just write the function as:

$(document).ready(function() {

function MyBlah(blah) {

This calls the function MyBlah on content ready.

Extracting double-digit months and days from a Python date

you can use a string formatter to pad any integer with zeros. It acts just like C's printf.

>>> d =
>>> '%02d' % d.month

Updated for py36: Use f-strings! For general ints you can use the d formatter and explicitly tell it to pad with zeros:

 >>> d =
 >>> f"{d.month:02d}"

But datetimes are special and come with special formatters that are already zero padded:

 >>> f"{d:%d}"  # the day
 >>> f"{d:%m}"  # the month

How to redirect output to a file and stdout

$ program [arguments...] 2>&1 | tee outfile

2>&1 dumps the stderr and stdout streams. tee outfile takes the stream it gets and writes it to the screen and to the file "outfile".

This is probably what most people are looking for. The likely situation is some program or script is working hard for a long time and producing a lot of output. The user wants to check it periodically for progress, but also wants the output written to a file.

The problem (especially when mixing stdout and stderr streams) is that there is reliance on the streams being flushed by the program. If, for example, all the writes to stdout are not flushed, but all the writes to stderr are flushed, then they'll end up out of chronological order in the output file and on the screen.

It's also bad if the program only outputs 1 or 2 lines every few minutes to report progress. In such a case, if the output was not flushed by the program, the user wouldn't even see any output on the screen for hours, because none of it would get pushed through the pipe for hours.

Update: The program unbuffer, part of the expect package, will solve the buffering problem. This will cause stdout and stderr to write to the screen and file immediately and keep them in sync when being combined and redirected to tee. E.g.:

$ unbuffer program [arguments...] 2>&1 | tee outfile

How to reset the bootstrap modal when it gets closed and open it fresh again?

Reset form inside the modal. Sample Code:

$('#myModal').on('', '#myModal', function (e) {
    $('#myModal form')[0].reset();

Check number of arguments passed to a Bash script

It might be a good idea to use arithmetic expressions if you're dealing with numbers.

if (( $# != 1 )); then
    >&2 echo "Illegal number of parameters"

>&2 is used to write the error message to stderr.

How can I get a JavaScript stack trace when I throw an exception?

An update to Eugene's answer: The error object must be thrown in order for IE (specific versions?) to populate the stack property. The following should work better than his current example, and should avoid returning undefined when in IE.

function stackTrace() {
  try {
    var err = new Error();
    throw err;
  } catch (err) {
    return err.stack;

Note 1: This sort of thing should only be done when debugging, and disabled when live, especially if called frequently. Note 2: This may not work in all browsers, but seems to work in FF and IE 11, which suits my needs just fine.

VC++ fatal error LNK1168: cannot open filename.exe for writing

This can also be a problem from the improper use of functions like FindNextFile when a FindClose is never executed. The process of the built file is terminated, and the build itself can be deleted, but LNK1168 will prevent a rebuild because of the open handle. This can create a handle leak in Explorer which can be addressed by terminating and restarting Explorer, but in many cases an immediate reboot is necessary.

Is < faster than <=?

Historically (we're talking the 1980s and early 1990s), there were some architectures in which this was true. The root issue is that integer comparison is inherently implemented via integer subtractions. This gives rise to the following cases.

Comparison     Subtraction
----------     -----------
A < B      --> A - B < 0
A = B      --> A - B = 0
A > B      --> A - B > 0

Now, when A < B the subtraction has to borrow a high-bit for the subtraction to be correct, just like you carry and borrow when adding and subtracting by hand. This "borrowed" bit was usually referred to as the carry bit and would be testable by a branch instruction. A second bit called the zero bit would be set if the subtraction were identically zero which implied equality.

There were usually at least two conditional branch instructions, one to branch on the carry bit and one on the zero bit.

Now, to get at the heart of the matter, let's expand the previous table to include the carry and zero bit results.

Comparison     Subtraction  Carry Bit  Zero Bit
----------     -----------  ---------  --------
A < B      --> A - B < 0    0          0
A = B      --> A - B = 0    1          1
A > B      --> A - B > 0    1          0

So, implementing a branch for A < B can be done in one instruction, because the carry bit is clear only in this case, , that is,

;; Implementation of "if (A < B) goto address;"
cmp  A, B          ;; compare A to B
bcz  address       ;; Branch if Carry is Zero to the new address

But, if we want to do a less-than-or-equal comparison, we need to do an additional check of the zero flag to catch the case of equality.

;; Implementation of "if (A <= B) goto address;"
cmp A, B           ;; compare A to B
bcz address        ;; branch if A < B
bzs address        ;; also, Branch if the Zero bit is Set

So, on some machines, using a "less than" comparison might save one machine instruction. This was relevant in the era of sub-megahertz processor speed and 1:1 CPU-to-memory speed ratios, but it is almost totally irrelevant today.

Is it possible to execute multiple _addItem calls asynchronously using Google Analytics?

From the docs:

_trackTrans() Sends both the transaction and item data to the Google Analytics server. This method should be called after _trackPageview(), and used in conjunction with the _addItem() and addTrans() methods. It should be called after items and transaction elements have been set up.

So, according to the docs, the items get sent when you call trackTrans(). Until you do, you can add items, but the transaction will not be sent.

Edit: Further reading led me here:

Where it clearly says you can start another transaction with an existing ID. When you commit it, the new items you listed will be added to that transaction.

No server in Eclipse; trying to install Tomcat

For future poeple who have the same problem: Try to add server tab from eclipse menu, if it doesnt work, then go do @Tomasz Bartnik solution above, and retry the following again:

  1. Go to WIndow > Show view > Other

    enter image description here

  2. search for servers, select it and press OK

    enter image description here

It will then be added to your tabs

Best way to copy a database (SQL Server 2008)

Easiest way is actually a script.

Run this on production:


TO DISK = 'C:\temp\MyDatabase1.bak' -- some writeable folder. 

This one command makes a complete backup copy of the database onto a single file, without interfering with production availability or backup schedule, etc.

To restore, just run this on your dev or test SQL Server:


FROM DISK = 'C:\temp\MyDatabase1.bak'
MOVE 'MyDatabase'   TO 'C:\Sql\MyDatabase.mdf', -- or wherever these live on target
MOVE 'MyDatabase_log'   TO 'C:\Sql\MyDatabase_log.ldf',

Then save these scripts on each server. One-click convenience.

if you get an error when restoring that the logical names don't match, you can get them like this:

FROM disk = 'C:\temp\MyDatabaseName1.bak'

If you use SQL Server logins (not windows authentication) you can run this after restoring each time (on the dev/test machine):

use MyDatabaseName;
sp_change_users_login 'Auto_Fix', 'userloginname', null, 'userpassword';

No operator matches the given name and argument type(s). You might need to add explicit type casts. -- Netbeans, Postgresql 8.4 and Glassfish

This the main error:

ERROR: operator does not exist: integer = character varying

You code is trying to match an integer and a string, that's not going to work. Fix your code, get the query that is involved to see if you fixed it. See also the PostgreSQL log files.

A workaround (NOT A SOLUTION!) is to do some casting. Check this article.

What is a raw type and why shouldn't we use it?

A "raw" type in Java is a class which is non-generic and deals with "raw" Objects, rather than type-safe generic type parameters.

For example, before Java generics was available, you would use a collection class like this:

LinkedList list = new LinkedList();
list.add(new MyObject());
MyObject myObject = (MyObject)list.get(0);

When you add your object to the list, it doesn't care what type of object it is, and when you get it from the list, you have to explicitly cast it to the type you are expecting.

Using generics, you remove the "unknown" factor, because you must explicitly specify which type of objects can go in the list:

LinkedList<MyObject> list = new LinkedList<MyObject>();
list.add(new MyObject());
MyObject myObject = list.get(0);

Notice that with generics you don't have to cast the object coming from the get call, the collection is pre-defined to only work with MyObject. This very fact is the main driving factor for generics. It changes a source of runtime errors into something that can be checked at compile time.

Create a folder and sub folder in Excel VBA

There are some good answers on here, so I will just add some process improvements. A better way of determining if the folder exists (does not use FileSystemObjects, which not all computers are allowed to use):

Function FolderExists(FolderPath As String) As Boolean
     FolderExists = True
     On Error Resume Next
     ChDir FolderPath
     If Err <> 0 Then FolderExists = False
     On Error GoTo 0
End Function


Function FileExists(FileName As String) As Boolean
     If Dir(FileName) <> "" Then FileExists = True Else FileExists = False

'innerText' works in IE, but not in Firefox

Update: I wrote a blog post detailing all the differences much better.

Firefox uses W3C standard Node::textContent, but its behavior differs "slightly" from that of MSHTML's proprietary innerText (copied by Opera as well, some time ago, among dozens of other MSHTML features).

First of all, textContent whitespace representation is different from innerText one. Second, and more importantly, textContent includes all of SCRIPT tag contents, whereas innerText doesn't.

Just to make things more entertaining, Opera - besides implementing standard textContent - decided to also add MSHTML's innerText but changed it to act as textContent - i.e. including SCRIPT contents (in fact, textContent and innerText in Opera seem to produce identical results, probably being just aliased to each other).

textContent is part of Node interface, whereas innerText is part of HTMLElement. This, for example, means that you can "retrieve" textContent but not innerText from text nodes:

var el = document.createElement('p');
var textNode = document.createTextNode('x');

el.textContent; // ""
el.innerText; // ""

textNode.textContent; // "x"
textNode.innerText; // undefined

Finally, Safari 2.x also has buggy innerText implementation. In Safari, innerText functions properly only if an element is neither hidden (via style.display == "none") nor orphaned from the document. Otherwise, innerText results in an empty string.

I was playing with textContent abstraction (to work around these deficiencies), but it turned out to be rather complex.

You best bet is to first define your exact requirements and follow from there. It is often possible to simply strip tags off of innerHTML of an element, rather than deal with all of the possible textContent/innerText deviations.

Another possibility, of course, is to walk the DOM tree and collect text nodes recursively.

Why am I getting InputMismatchException?

Here you can see the nature of Scanner:

double nextDouble()

Returns the next token as a double. If the next token is not a float or is out of range, InputMismatchException is thrown.

Try to catch the exception

try {
    // ...
} catch (InputMismatchException e) {
    System.out.print(e.getMessage()); //try to find out specific reason.



I tried your code and there is nothing wrong with it. Your are getting that error because you must have entered String value. When I entered a numeric value, it runs without any errors. But once I entered String it throw the same Exception which you have mentioned in your question.


You have entered something, which is out of range as I have mentioned above.

I'm really wondering what you could have tried to enter. In my system, it is running perfectly without changing a single line of code. Just copy as it is and try to compile and run it.

import java.util.*;

public class Test {
    public static void main(String... args) {
        new Test().askForMarks(5);

    public void askForMarks(int student) {
        double marks[] = new double[student];
        int index = 0;
        Scanner reader = new Scanner(;
        while (index < student) {
            System.out.print("Please enter a mark (0..30): ");
            marks[index] = (double) checkValueWithin(0, 30); 

    public double checkValueWithin(int min, int max) {
        double num;
        Scanner reader = new Scanner(;
        num = reader.nextDouble();                         
        while (num < min || num > max) {                 
            System.out.print("Invalid. Re-enter number: "); 
            num = reader.nextDouble();                         

        return num;

As you said, you have tried to enter 1.0, 2.8 and etc. Please try with this code.

Note : Please enter number one by one, on separate lines. I mean, enter 2.7, press enter and then enter second number (e.g. 6.7).

Adding new column to existing DataFrame in Python pandas

I would like to add a new column, 'e', to the existing data frame and do not change anything in the data frame. (The series always got the same length as a dataframe.)

I assume that the index values in e match those in df1.

The easiest way to initiate a new column named e, and assign it the values from your series e:

df['e'] = e.values

assign (Pandas 0.16.0+)

As of Pandas 0.16.0, you can also use assign, which assigns new columns to a DataFrame and returns a new object (a copy) with all the original columns in addition to the new ones.

df1 = df1.assign(e=e.values)

As per this example (which also includes the source code of the assign function), you can also include more than one column:

df = pd.DataFrame({'a': [1, 2], 'b': [3, 4]})
>>> df.assign(mean_a=df.a.mean(), mean_b=df.b.mean())
   a  b  mean_a  mean_b
0  1  3     1.5     3.5
1  2  4     1.5     3.5

In context with your example:

df1 = pd.DataFrame(np.random.randn(10, 4), columns=['a', 'b', 'c', 'd'])
mask = df1.applymap(lambda x: x <-0.7)
df1 = df1[-mask.any(axis=1)]
sLength = len(df1['a'])
e = pd.Series(np.random.randn(sLength))

>>> df1
          a         b         c         d
0  1.764052  0.400157  0.978738  2.240893
2 -0.103219  0.410599  0.144044  1.454274
3  0.761038  0.121675  0.443863  0.333674
7  1.532779  1.469359  0.154947  0.378163
9  1.230291  1.202380 -0.387327 -0.302303

>>> e
0   -1.048553
1   -1.420018
2   -1.706270
3    1.950775
4   -0.509652
dtype: float64

df1 = df1.assign(e=e.values)

>>> df1
          a         b         c         d         e
0  1.764052  0.400157  0.978738  2.240893 -1.048553
2 -0.103219  0.410599  0.144044  1.454274 -1.420018
3  0.761038  0.121675  0.443863  0.333674 -1.706270
7  1.532779  1.469359  0.154947  0.378163  1.950775
9  1.230291  1.202380 -0.387327 -0.302303 -0.509652

The description of this new feature when it was first introduced can be found here.

How to combine two lists in R

I was looking to do the same thing, but to preserve the list as a just an array of strings so I wrote a new code, which from what I've been reading may not be the most efficient but worked for what i needed to do:

combineListsAsOne <-function(list1, list2){
  n <- c()
  for(x in list1){
    n<-c(n, x)
  for(y in list2){
    n<-c(n, y)

It just creates a new list and adds items from two supplied lists to create one.

What is the difference between user and kernel modes in operating systems?

CPU rings are the most clear distinction

In x86 protected mode, the CPU is always in one of 4 rings. The Linux kernel only uses 0 and 3:

  • 0 for kernel
  • 3 for users

This is the most hard and fast definition of kernel vs userland.

Why Linux does not use rings 1 and 2: CPU Privilege Rings: Why rings 1 and 2 aren't used?

How is the current ring determined?

The current ring is selected by a combination of:

  • global descriptor table: a in-memory table of GDT entries, and each entry has a field Privl which encodes the ring.

    The LGDT instruction sets the address to the current descriptor table.

    See also:

  • the segment registers CS, DS, etc., which point to the index of an entry in the GDT.

    For example, CS = 0 means the first entry of the GDT is currently active for the executing code.

What can each ring do?

The CPU chip is physically built so that:

  • ring 0 can do anything

  • ring 3 cannot run several instructions and write to several registers, most notably:

    • cannot change its own ring! Otherwise, it could set itself to ring 0 and rings would be useless.

      In other words, cannot modify the current segment descriptor, which determines the current ring.

    • cannot modify the page tables: How does x86 paging work?

      In other words, cannot modify the CR3 register, and paging itself prevents modification of the page tables.

      This prevents one process from seeing the memory of other processes for security / ease of programming reasons.

    • cannot register interrupt handlers. Those are configured by writing to memory locations, which is also prevented by paging.

      Handlers run in ring 0, and would break the security model.

      In other words, cannot use the LGDT and LIDT instructions.

    • cannot do IO instructions like in and out, and thus have arbitrary hardware accesses.

      Otherwise, for example, file permissions would be useless if any program could directly read from disk.

      More precisely thanks to Michael Petch: it is actually possible for the OS to allow IO instructions on ring 3, this is actually controlled by the Task state segment.

      What is not possible is for ring 3 to give itself permission to do so if it didn't have it in the first place.

      Linux always disallows it. See also: Why doesn't Linux use the hardware context switch via the TSS?

How do programs and operating systems transition between rings?

  • when the CPU is turned on, it starts running the initial program in ring 0 (well kind of, but it is a good approximation). You can think this initial program as being the kernel (but it is normally a bootloader that then calls the kernel still in ring 0).

  • when a userland process wants the kernel to do something for it like write to a file, it uses an instruction that generates an interrupt such as int 0x80 or syscall to signal the kernel. x86-64 Linux syscall hello world example:

        .ascii "hello world\n"
        hello_world_len = . - hello_world
    .global _start
        /* write */
        mov $1, %rax
        mov $1, %rdi
        mov $hello_world, %rsi
        mov $hello_world_len, %rdx
        /* exit */
        mov $60, %rax
        mov $0, %rdi

    compile and run:

    as -o hello_world.o hello_world.S
    ld -o hello_world.out hello_world.o

    GitHub upstream.

    When this happens, the CPU calls an interrupt callback handler which the kernel registered at boot time. Here is a concrete baremetal example that registers a handler and uses it.

    This handler runs in ring 0, which decides if the kernel will allow this action, do the action, and restart the userland program in ring 3. x86_64

  • when the exec system call is used (or when the kernel will start /init), the kernel prepares the registers and memory of the new userland process, then it jumps to the entry point and switches the CPU to ring 3

  • If the program tries to do something naughty like write to a forbidden register or memory address (because of paging), the CPU also calls some kernel callback handler in ring 0.

    But since the userland was naughty, the kernel might kill the process this time, or give it a warning with a signal.

  • When the kernel boots, it setups a hardware clock with some fixed frequency, which generates interrupts periodically.

    This hardware clock generates interrupts that run ring 0, and allow it to schedule which userland processes to wake up.

    This way, scheduling can happen even if the processes are not making any system calls.

What is the point of having multiple rings?

There are two major advantages of separating kernel and userland:

  • it is easier to make programs as you are more certain one won't interfere with the other. E.g., one userland process does not have to worry about overwriting the memory of another program because of paging, nor about putting hardware in an invalid state for another process.
  • it is more secure. E.g. file permissions and memory separation could prevent a hacking app from reading your bank data. This supposes, of course, that you trust the kernel.

How to play around with it?

I've created a bare metal setup that should be a good way to manipulate rings directly:

I didn't have the patience to make a userland example unfortunately, but I did go as far as paging setup, so userland should be feasible. I'd love to see a pull request.

Alternatively, Linux kernel modules run in ring 0, so you can use them to try out privileged operations, e.g. read the control registers: How to access the control registers cr0,cr2,cr3 from a program? Getting segmentation fault

Here is a convenient QEMU + Buildroot setup to try it out without killing your host.

The downside of kernel modules is that other kthreads are running and could interfere with your experiments. But in theory you can take over all interrupt handlers with your kernel module and own the system, that would be an interesting project actually.

Negative rings

While negative rings are not actually referenced in the Intel manual, there are actually CPU modes which have further capabilities than ring 0 itself, and so are a good fit for the "negative ring" name.

One example is the hypervisor mode used in virtualization.

For further details see:


In ARM, the rings are called Exception Levels instead, but the main ideas remain the same.

There exist 4 exception levels in ARMv8, commonly used as:

  • EL0: userland

  • EL1: kernel ("supervisor" in ARM terminology).

    Entered with the svc instruction (SuperVisor Call), previously known as swi before unified assembly, which is the instruction used to make Linux system calls. Hello world ARMv8 example:


    .global _start
        /* write */
        mov x0, 1
        ldr x1, =msg
        ldr x2, =len
        mov x8, 64
        svc 0
        /* exit */
        mov x0, 0
        mov x8, 93
        svc 0
        .ascii "hello syscall v8\n"
    len = . - msg

    GitHub upstream.

    Test it out with QEMU on Ubuntu 16.04:

    sudo apt-get install qemu-user gcc-arm-linux-gnueabihf
    arm-linux-gnueabihf-as -o hello.o hello.S
    arm-linux-gnueabihf-ld -o hello hello.o
    qemu-arm hello

    Here is a concrete baremetal example that registers an SVC handler and does an SVC call.

  • EL2: hypervisors, for example Xen.

    Entered with the hvc instruction (HyperVisor Call).

    A hypervisor is to an OS, what an OS is to userland.

    For example, Xen allows you to run multiple OSes such as Linux or Windows on the same system at the same time, and it isolates the OSes from one another for security and ease of debug, just like Linux does for userland programs.

    Hypervisors are a key part of today's cloud infrastructure: they allow multiple servers to run on a single hardware, keeping hardware usage always close to 100% and saving a lot of money.

    AWS for example used Xen until 2017 when its move to KVM made the news.

  • EL3: yet another level. TODO example.

    Entered with the smc instruction (Secure Mode Call)

The ARMv8 Architecture Reference Model DDI 0487C.a - Chapter D1 - The AArch64 System Level Programmer's Model - Figure D1-1 illustrates this beautifully:

enter image description here

The ARM situation changed a bit with the advent of ARMv8.1 Virtualization Host Extensions (VHE). This extension allows the kernel to run in EL2 efficiently:

enter image description here

VHE was created because in-Linux-kernel virtualization solutions such as KVM have gained ground over Xen (see e.g. AWS' move to KVM mentioned above), because most clients only need Linux VMs, and as you can imagine, being all in a single project, KVM is simpler and potentially more efficient than Xen. So now the host Linux kernel acts as the hypervisor in those cases.

Note how ARM, maybe due to the benefit of hindsight, has a better naming convention for the privilege levels than x86, without the need for negative levels: 0 being the lower and 3 highest. Higher levels tend to be created more often than lower ones.

The current EL can be queried with the MRS instruction: what is the current execution mode/exception level, etc?

ARM does not require all exception levels to be present to allow for implementations that don't need the feature to save chip area. ARMv8 "Exception levels" says:

An implementation might not include all of the Exception levels. All implementations must include EL0 and EL1. EL2 and EL3 are optional.

QEMU for example defaults to EL1, but EL2 and EL3 can be enabled with command line options: qemu-system-aarch64 entering el1 when emulating a53 power up

Code snippets tested on Ubuntu 18.10.

Using setTimeout to delay timing of jQuery actions

You can also use jQuery's delay() method instead of setTimeout(). It'll give you much more readable code. Here's an example from the docs:

$( "#foo" ).slideUp( 300 ).delay( 800 ).fadeIn( 400 );

The only limitation (that I'm aware of) is that it doesn't give you a way to clear the timeout. If you need to do that then you're better off sticking with all the nested callbacks that setTimeout thrusts upon you.

How do I draw a set of vertical lines in gnuplot?

alternatively you can also do this:

p '< echo "x y"' w impulse

x and y are the coordinates of the point to which you draw a vertical bar

How can the error 'Client found response content type of 'text/html'.. be interpreted

This is happening because there is an unhandled exception in your Web service, and the .NET runtime is spitting out its HTML yellow screen of death server error/exception dump page, instead of XML.

Since the consumer of your Web service was expecting a text/xml header and instead got text/html, it throws that error.

You should address the cause of your timeouts (perhaps a lengthy SQL query?).

Also, checkout this blog post on Jeff Atwood's blog that explains implementing a global unhandled exception handler and using SOAP exceptions.

How to read single Excel cell value

The issue with reading single Excel Cell in .Net comes from the fact, that the empty cell is evaluated to a Null. Thus, one cannot use its .Value or .Value2 properties, because an error shows up.

To return an empty string, when the cell is Null the Convert.ToString(Cell) can be used in the following way:

Excel.Workbook wkb = Open(excel, filePath);
Excel.Worksheet wk = (Excel.Worksheet)excel.Worksheets.get_Item(1);

for (int i = 1; i < 5; i++)
    string a = Convert.ToString(wk.Cells[i, 1].Value2);

How to set Toolbar text and back arrow color

< xmlns:android=""


<!-- ToolBar -->
<style name="ToolBarStyle" parent="Widget.AppCompat.Toolbar">
    <item name="actionMenuTextColor">#ff63BBF7</item>

use app:theme="@style/ToolBarStyle"

Reference resources:

TypeError: a bytes-like object is required, not 'str' when writing to a file in Python3

I got this error when I was trying to convert a char (or string) to bytes, the code was something like this with Python 2.7:

# -*- coding: utf-8 -*-
print( bytes('ò') )

This is the way of Python 2.7 when dealing with unicode chars.

This won't work with Python 3.6, since bytes require an extra argument for encoding, but this can be little tricky, since different encoding may output different result:

print( bytes('ò', 'iso_8859_1') ) # prints: b'\xf2'
print( bytes('ò', 'utf-8') ) # prints: b'\xc3\xb2'

In my case I had to use iso_8859_1 when encoding bytes in order to solve the issue.

Hope this helps someone.

Accessing last x characters of a string in Bash

You can use tail:

$ foo="1234567890"
$ echo -n $foo | tail -c 3

A somewhat roundabout way to get the last three characters would be to say:

echo $foo | rev | cut -c1-3 | rev

How to use UIPanGestureRecognizer to move object? iPhone/iPad

UIPanGestureRecognizer * pan1 = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(moveObject:)];
pan1.minimumNumberOfTouches = 1;
[image1 addGestureRecognizer:pan1];

-(void)moveObject:(UIPanGestureRecognizer *)pan;
{ = [pan locationInView:image1.superview];

Getting rid of all the rounded corners in Twitter Bootstrap

The code posted above by @BrunoS did not work for me,

* {
  .border-radius(0) !important;

what i used was

* {
  border-radius: 0 !important;

I hope this helps someone

What are SP (stack) and LR in ARM?

LR is link register used to hold the return address for a function call.

SP is stack pointer. The stack is generally used to hold "automatic" variables and context/parameters across function calls. Conceptually you can think of the "stack" as a place where you "pile" your data. You keep "stacking" one piece of data over the other and the stack pointer tells you how "high" your "stack" of data is. You can remove data from the "top" of the "stack" and make it shorter.

From the ARM architecture reference:

SP, the Stack Pointer

Register R13 is used as a pointer to the active stack.

In Thumb code, most instructions cannot access SP. The only instructions that can access SP are those designed to use SP as a stack pointer. The use of SP for any purpose other than as a stack pointer is deprecated. Note Using SP for any purpose other than as a stack pointer is likely to break the requirements of operating systems, debuggers, and other software systems, causing them to malfunction.

LR, the Link Register

Register R14 is used to store the return address from a subroutine. At other times, LR can be used for other purposes.

When a BL or BLX instruction performs a subroutine call, LR is set to the subroutine return address. To perform a subroutine return, copy LR back to the program counter. This is typically done in one of two ways, after entering the subroutine with a BL or BLX instruction:

• Return with a BX LR instruction.

• On subroutine entry, store LR to the stack with an instruction of the form: PUSH {,LR} and use a matching instruction to return: POP {,PC} ...

This link gives an example of a trivial subroutine.

Here is an example of how registers are saved on the stack prior to a call and then popped back to restore their content.

select certain columns of a data table

Here's working example with anonymous output record, if you have any questions place a comment below:                    

public partial class Form1 : Form
    DataTable table;
    public Form1()
        #region TestData
        table = new DataTable();
        for (int i = 1; i < 12; ++i)
            table.Columns.Add("Col" + i);
        for (int rowIndex = 0; rowIndex < 5; ++rowIndex)
            DataRow row = table.NewRow();
            for (int i = 0; i < table.Columns.Count; ++i)
                row[i] = String.Format("row:{0},col:{1}", rowIndex, i);

    public void bind()
        var filtered = from t in table.AsEnumerable()
                       select new
                           col1 = t.Field<string>(0),//column of index 0 = "Col1"
                           col2 = t.Field<string>(1),//column of index 1 = "Col2"
                           col3 = t.Field<string>(5),//column of index 5 = "Col6"
                           col4 = t.Field<string>(6),//column of index 6 = "Col7"
                           col5 = t.Field<string>(4),//column of index 4 = "Col3"
        filteredData.AutoGenerateColumns = true;
        filteredData.DataSource = filtered.ToList();

Cannot read property 'map' of undefined

The error "Cannot read property 'map' of undefined" will be encountered if there is an error in the "" or there is no array.

Better put condition to check the the array like


How to set environment variables in PyCharm?

This is what you can do to source an .env (and .flaskenv) file in the pycharm flask/django console. It would also work for a normal python console of course.

  1. Do pip install python-dotenv in your environment (the same as being pointed to by pycharm).

  2. Go to: Settings > Build ,Execution, Deployment > Console > Flask/django Console

  3. In "starting script" include something like this near the top:

    from dotenv import load_dotenv load_dotenv(verbose=True)

The .env file can look like this: export KEY=VALUE

It doesn't matter if one includes export or not for dotenv to read it.

As an alternative you could also source the .env file in the activate shell script for the respective virtual environement.

Arduino Sketch upload issue - avrdude: stk500_recv(): programmer is not responding

I had this problem with a Crowduino, running the Arduino IDE on OS X. The solution for me was to switch on verbose output during upload (in the Arduino IDE preferences pane).

Then, when uploading, you can see AVRDUDE sending three packets avrdude: Send: 0 [30] [20] (with corresponding RX flashes on the board) right before the avrdude: ser_recv(): programmer is not responding error.

The trick is to hit the reset button on the board immediately before these three packets are sent. Then the program will be uploaded successfully.

Difference between 3NF and BCNF in simple terms (must be able to explain to an 8-year old)

The subtle difference is that 3NF makes a distinction between key and non-key attributes (also called non-prime attributes) whereas BCNF does not.

This is best explained using Zaniolo's definition of 3NF, which is equivalent to Codd's:

A relation, R, is in 3NF iff for every nontrivial FD (X->A) satisfied by R at least ONE of the following conditions is true:

(a) X is a superkey for R, or

(b) A is a key attribute for R

BCNF requires (a) but doesn't treat (b) as a special case of its own. In other words BCNF requires that every nontrivial determinant is a superkey even its dependent attributes happen to be part of a key.

A relation, R, is in BCNF iff for every nontrivial FD (X->A) satisfied by R the following condition is true:

(a) X is a superkey for R

BCNF is therefore more strict.

The difference is so subtle that what many people informally describe as 3NF is actually BCNF. For example, you stated here that 3NF means "data depends on the key[s]... and nothing but the key[s]", but that is really an informal description of BCNF and not 3NF. 3NF could more accurately be described as "non-key data depends on the keys... and nothing but the keys".

You also stated:

the 3NF quote explicitly says "nothing but the key" meaning that all attributes depend solely on the primary key.

That's an oversimplification. 3NF and BCNF and all the Normal Forms are concerned with all candidate keys and/or superkeys, not just one "primary" key.

Is it possible to Turn page programmatically in UIPageViewController?

Here's another code example for a single paged view. Implementation for viewControllerAtIndex is omitted here, it should return the correct view controller for the given index.

- (void)changePage:(UIPageViewControllerNavigationDirection)direction {
    NSUInteger pageIndex = ((FooViewController *) [_pageViewController.viewControllers objectAtIndex:0]).pageIndex;

    if (direction == UIPageViewControllerNavigationDirectionForward) {
    else {

    FooViewController *viewController = [self viewControllerAtIndex:pageIndex];

    if (viewController == nil) {

    [_pageViewController setViewControllers:@[viewController]

Pages can be changed by calling

[self changePage:UIPageViewControllerNavigationDirectionReverse];
[self changePage:UIPageViewControllerNavigationDirectionForward];

Delete element in a slice

I'm getting an index out of range error with the accepted answer solution. Reason: When range start, it is not iterate value one by one, it is iterate by index. If you modified a slice while it is in range, it will induce some problem.

Old Answer:

chars := []string{"a", "a", "b"}

for i, v := range chars {
    fmt.Printf("%+v, %d, %s\n", chars, i, v)
    if v == "a" {
        chars = append(chars[:i], chars[i+1:]...)
fmt.Printf("%+v", chars)

Expected :

[a a b], 0, a
[a b], 0, a
[b], 0, b
Result: [b]


// Autual
[a a b], 0, a
[a b], 1, b
[a b], 2, b
Result: [a b]

Correct Way (Solution):

chars := []string{"a", "a", "b"}

for i := 0; i < len(chars); i++ {
    if chars[i] == "a" {
        chars = append(chars[:i], chars[i+1:]...)
        i-- // form the remove item index to start iterate next item

fmt.Printf("%+v", chars)


Uncaught TypeError: Cannot set property 'onclick' of null

Wrap code in

window.onload = function(){ 
    // your code 

how to set the query timeout from SQL connection string

See:- ConnectionStrings content on this subject. There is no default command timeout property.

How to get a list of installed android applications and pick one to run

Since Android 11 (API level 30), most user-installed apps are not visible by default. You must either statically declare which apps and/or intent filters you are going to get info about in your manifest like this:

        <!-- Explicit apps you know in advance about: -->
        <package android:name=""/>
        <package android:name=""/>

        <!-- Intent filter signatures that you are going to query: -->
            <action android:name="android.intent.action.SEND" />
            <data android:mimeType="image/jpeg" />

Or require the QUERY_ALL_PACKAGES permission.

After doing the above, the other answers here still apply.

Learn more here:

how do I get a new line, after using float:left?

Try the clear property.

Remember that float removes an element from the document layout - so yes, in a way it is "interfering" with br and p tags, in the sense that it would basically be ignoring anything in the main flow layout.

Append file contents to the bottom of existing file in Bash

This should work:

 cat "$API" >> "$CONFIG"

You need to use the >> operator to append to a file. Redirecting with > causes the file to be overwritten. (truncated).

How to Uninstall RVM?

It’s easy; just do the following:

rvm implode


rm -rf ~/.rvm

And don’t forget to remove the script calls in the following files:

  • ~/.bashrc
  • ~/.bash_profile
  • ~/.profile

And maybe others depending on whatever shell you’re using.

failed to lazily initialize a collection of role

Try swich fetchType from LAZY to EAGER

private Set<NodeValue> nodeValues;

But in this case your app will fetch data from DB anyway. If this query very hard - this may impact on performance. More here:

==> 73

Each for object?

var object = { "a": 1, "b": 2};_x000D_
$.each(object, function(key, value){_x000D_
  console.log(key + ": " + object[key]);_x000D_
<script src=""></script>

a: 1
b: 2

Compiler error: memset was not declared in this scope

You should include <string.h> (or its C++ equivalent, <cstring>).

`col-xs-*` not working in Bootstrap 4

I just wondered, why col-xs-6 did not work for me but then I found the answer in the Bootstrap 4 documentation. The class prefix for extra small devices is now col- while in the previous versions it was col-xs.

Bootstrap 4 dropped all col-xs-* classes, so use col-* instead. For example col-xs-6 replaced by col-6.

What is the default boolean value in C#?

Try this (using default keyword)

 bool foo = default(bool); if (foo) { } 

unbound method f() must be called with fibo_ instance as first argument (got classobj instance instead)

Differences in In python 2 and 3 version:

If you already have a default method in a class with same name and you re-declare as a same name it will appear as unbound-method call of that class instance when you wanted to instantiated it.

If you wanted class methods, but you declared them as instance methods instead.

An instance method is a method that is used when to create an instance of the class.

An example would be

   def user_group(self):   #This is an instance method
        return "instance method returning group"

Class label method:

   def user_group(groups):   #This is an class-label method
        return "class method returning group"

In python 2 and 3 version differ the class @classmethod to write in python 3 it automatically get that as a class-label method and don't need to write @classmethod I think this might help you.

What does request.getParameter return?

Both if (one.length() > 0) {} and if (!"".equals(one)) {} will check against an empty foo parameter, and an empty parameter is what you'd get if the the form is submitted with no value in the foo text field.

If there's any chance you can use the Expression Language to handle the parameter, you could access it with empty in an expression.

<c:if test='${not empty}'>
    This page code gets rendered.

RequestDispatcher.forward() vs HttpServletResponse.sendRedirect()

Simply difference between Forward(ServletRequest request, ServletResponse response) and sendRedirect(String url) is


  1. The forward() method is executed in the server side.
  2. The request is transfer to other resource within same server.
  3. It does not depend on the client’s request protocol since the forward () method is provided by the servlet container.
  4. The request is shared by the target resource.
  5. Only one call is consumed in this method.
  6. It can be used within server.
  7. We cannot see forwarded message, it is transparent.
  8. The forward() method is faster than sendRedirect() method.
  9. It is declared in RequestDispatcher interface.


  1. The sendRedirect() method is executed in the client side.
  2. The request is transfer to other resource to different server.
  3. The sendRedirect() method is provided under HTTP so it can be used only with HTTP clients.
  4. New request is created for the destination resource.
  5. Two request and response calls are consumed.
  6. It can be used within and outside the server.
  7. We can see redirected address, it is not transparent.
  8. The sendRedirect() method is slower because when new request is created old request object is lost.
  9. It is declared in HttpServletResponse.

How to set the color of an icon in Angular Material?

That's because the color input only accepts three attributes: "primary", "accent" or "warn". Hence, you'll have to style the icons the CSS way:

  1. Add a class to style your icon:

    .white-icon {
        color: white;
    /* Note: If you're using an SVG icon, you should make the class target the `<svg>` element */
    .white-icon svg {
        fill: white;
  2. Add the class to your icon:

    <mat-icon class="white-icon">menu</mat-icon>

cout is not a member of std

I had a similar issue and it turned out that i had to add an extra entry in cmake to include the files.

Since i was also using the zmq library I had to add this to the included libraries as well.

Filtering a data frame by values in a column

The subset command is not necessary. Just use data frame indexing

studentdata[studentdata$Drink == 'water',]

Read the warning from ?subset

This is a convenience function intended for use interactively. For programming it is better to use the standard subsetting functions like ‘[’, and in particular the non-standard evaluation of argument ‘subset’ can have unanticipated consequences.

What is the difference between angular-route and angular-ui-router?

ui router make your life easier! You can add it to you AngularJS application via injecting it into your applications...

ng-route comes as part of the core AngularJS, so it's simpler and gives you fewer options...

Look at here to understand ng-route better:

Also when using it, don't forget to use: ngView ..

ng-ui-router is different but: but gives you more options....

How do I convert csv file to rdd

I'd recommend reading the header directly from the driver, not through Spark. Two reasons for this: 1) It's a single line. There's no advantage to a distributed approach. 2) We need this line in the driver, not the worker nodes.

It goes something like this:

// Ridiculous amount of code to read one line.
val uri = new
val conf = sc.hadoopConfiguration
val fs = hadoop.fs.FileSystem.get(uri, conf)
val path = new hadoop.fs.Path(filename)
val stream =
val source =
val header = source.getLines.head

Now when you make the RDD you can discard the header.

val csvRDD = sc.textFile(filename).filter(_ != header)

Then we can make an RDD from one column, for example:

val idx = header.split(",").indexOf(columnName)
val columnRDD =",")(idx))

What does ON [PRIMARY] mean?

ON [PRIMARY] will create the structures on the "Primary" filegroup. In this case the primary key index and the table will be placed on the "Primary" filegroup within the database.

Conditional operator in Python?

From Python 2.5 onwards you can do:

value = b if a > 10 else c

Previously you would have to do something like the following, although the semantics isn't identical as the short circuiting effect is lost:

value = [c, b][a > 10]

There's also another hack using 'and ... or' but it's best to not use it as it has an undesirable behaviour in some situations that can lead to a hard to find bug. I won't even write the hack here as I think it's best not to use it, but you can read about it on Wikipedia if you want.

ORA-00918: column ambiguously defined in SELECT *

A query's projection can only have one instance of a given name. As your WHERE clause shows, you have several tables with a column called ID. Because you are selecting * your projection will have several columns called ID. Or it would have were it not for the compiler hurling ORA-00918.

The solution is quite simple: you will have to expand the projection to explicitly select named columns. Then you can either leave out the duplicate columns, retaining just (say) COACHES.ID or use column aliases: as COACHES_ID.

Perhaps that strikes you as a lot of typing, but it is the only way. If it is any comfort, SELECT * is regarded as bad practice in production code: explicitly named columns are much safer.

Javascript "Not a Constructor" Exception while creating objects

In my case I'd forgotten the open and close parantheses at the end of the definition of the function wrapping all of my code in the exported module. I.e. I had:

(function () {
  'use strict';

  module.exports.MyClass = class{

Instead of:

(function () {
  'use strict';

  module.exports.MyClass = class{

The compiler doesn't complain, but the require statement in the importing module doesn't set the variable it's being assigned to, so it's undefined at the point you try to construct it and it will give the TypeError: MyClass is not a constructor error.

right align an image using CSS HTML

My workaround for this issue was to set display: inline to the image element. With this, your image and text will be aligned to the right if you set text-align: right from a parent container.

How to retrieve a user environment variable in CMake (Windows)

Getting variables into your CMake script

You can pass a variable on the line with the cmake invocation:

FOO=1 cmake

or by exporting a variable in BASH:

export FOO=1

Then you can pick it up in a cmake script using:


How can I read Chrome Cache files?

EDIT: The below answer no longer works see here

If the file you try to recover has Content-Encoding: gzip in the header section, and you are using linux (or as in my case, you have Cygwin installed) you can do the following:

  1. visit chrome://view-http-cache/ and click the page you want to recover
  2. copy the last (fourth) section of the page verbatim to a text file (say: a.txt)
  3. xxd -r a.txt| gzip -d

Note that other answers suggest passing -p option to xxd - I had troubles with that presumably because the fourth section of the cache is not in the "postscript plain hexdump style" but in a "default style".

It also does not seem necessary to replace double spaces with a single space, as is doing (in case it is necessary you can use sed 's/ / /g' for that).

How to manage Angular2 "expression has changed after it was checked" exception when a component property depends on current datetime


ngAfterViewInit() {
    setTimeout(() => {
        this.dateNow = new Date();

Although this is a workaround, sometimes it's really hard to solve this issue in any nicer way, so don't blame yourself if you are using this approach. That's okay.

Examples: The initial issue [link], Solved with setTimeout() [link]

How to avoid

In general this error usually happens after you add somewhere (even in parent/child components) ngAfterViewInit. So first question is to ask yourself - can I live without ngAfterViewInit? Perhaps you move the code somewhere ( ngAfterViewChecked might be an alternative).

Example: [link]


Also async stuff in ngAfterViewInit that affects DOM might cause this. Also can be solved via setTimeout or by adding the delay(0) operator in the pipe:

ngAfterViewInit() {$
    .pipe(delay(0)) //"delay" here is an alternative to setTimeout()

Example: [link]

Nice Reading

Good article about how to debug this and why it happens: link

Openssl : error "self signed certificate in certificate chain"

If you're running Charles and trying to build a container then you'll most likely get this error.

Make sure to disable Charles (macos) proxy under proxy -> macOS proxy

Charles is an

HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet.

So anything similar may cause the same issue.

Can inner classes access private variables?

An inner class has access to all members of the outer class, but it does not have an implicit reference to a parent class instance (unlike some weirdness with Java). So if you pass a reference to the outer class to the inner class, it can reference anything in the outer class instance.

SELECT * FROM X WHERE id IN (...) with Dapper ORM

In my case I've used this:

var query = "select * from table where Id IN @Ids";
var result = conn.Query<MyEntity>(query, new { Ids = ids });

my variable "ids" in the second line is an IEnumerable of strings, also they can be integers I guess.

Insert auto increment primary key to existing table

I was able to adapt these instructions take a table with an existing non-increment primary key, and add an incrementing primary key to the table and create a new composite primary key with both the old and new keys as a composite primary key using the following code:


       USER_ID             VARCHAR (99) NOT NULL,
       EID                 VARCHAR (255) NOT NULL,

INSERT INTO SAKAI_USER_ID_MAP VALUES ('postmaster', 'postmaster');


When this is done, the _USER_ID field exists and has all number values for the primary key exactly as you would expect. With the "DROP TABLE" at the top, you can run this over and over to experiment with variations.

What I have not been able to get working is the situation where there are incoming FOREIGN KEYs that already point at the USER_ID field. I get this message when I try to do a more complex example with an incoming foreign key from another table.

#1025 - Error on rename of './zap/#sql-da07_6d' to './zap/SAKAI_USER_ID_MAP' (errno: 150)

I am guessing that I need to tear down all foreign keys before doing the ALTER table and then rebuild them afterwards. But for now I wanted to share this solution to a more challenging version of the original question in case others ran into this situation.

'Missing recommended icon file - The bundle does not contain an app icon for iPhone / iPod Touch of exactly '120x120' pixels, in .png format'

For generating icons for your Xcode projects, I'd suggest you consider using SquareIcon. I believe that it makes creating app icon sets for Apple platforms very easy. Just to let you know, this is my own app.

You can drop in a generic image file of your icon (like a PNG or JPG) and generate a .appiconset file which you can put in your Xcode project's asset catalog. This removes the requirement of manually resizing a bunch of images.

how to find 2d array size in c++

Use an std::vector.

std::vector< std::vector<int> > my_array; /* 2D Array */

my_array.size(); /* size of y */
my_array[0].size(); /* size of x */

Or, if you can only use a good ol' array, you can use sizeof.

sizeof( my_array ); /* y size */
sizeof( my_array[0] ); /* x size */

How to cast int to enum in C++?

Test castEnum = static_cast<Test>(a-1); will cast a to A. If you don't want to substruct 1, you can redefine the enum:

enum Test
    A:1, B

In this case Test castEnum = static_cast<Test>(a); could be used to cast a to A.

Creating an empty list in Python

Just to highlight @Darkonaut answer because I think it should be more visible.

new_list = [] or new_list = list() are both fine (ignoring performance), but append() returns None, as result you can't do new_list = new_list.append(something).

Mathematical functions in Swift

To be perfectly precise, Darwin is enough. No need to import the whole Cocoa framework.

import Darwin

Of course, if you need elements from Cocoa or Foundation or other higher level frameworks, you can import them instead

Get current controller in view

You are still in the context of your CategoryController even though you're loading a PartialView from your Views/News folder.

What's the difference between import java.util.*; and import java.util.Date; ?

but what I got is something like this: Date@124bbbf  
while I change the import to: import java.util.Date;  
the code works perfectly, why? 

What do you mean by "works perfectly"? The output of printing a Date object is the same no matter whether you imported java.util.* or java.util.Date. The output that you get when printing objects is the representation of the object by the toString() method of the corresponding class.

VLook-Up Match first 3 characters of one column with another column


Left is because you are starting the word/alphanumeric text from the left. the number "1" which i have placed is after lookup value in this case "A1" is because my search includes the formula for 1st character. If second character is asked it would be (A1,2) quite simple really :)

PHP check if url parameter exists

    // Do something

You want something like that

Android Studio - debug keystore

If you use Windows, probably the location is like this:


PHP Get Highest Value from Array

If you just want the largest value in the array use the max function. This will return the largest value, although not the corresponding key. It does not change the original array.

If you care about the the key you could then do

$key = array_search(max($array), $array)

(Edited to include @binaryLV's suggestion)

Choosing a jQuery datagrid plugin?

The three most used and well supported jQuery grid plugins today are SlickGrid, jqGrid and DataTables. See for more info.

Java method to sum any number of ints

You need:

public int sumAll(int...numbers){

    int result = 0;
    for(int i = 0 ; i < numbers.length; i++) {
        result += numbers[i];
    return result;

Then call the method and give it as many int values as you need:

int result = sumAll(1,4,6,3,5,393,4,5);//.....

What does API level mean?

An API is ready-made source code library.

In Java for example APIs are a set of related classes and interfaces that come in packages. This picture illustrates the libraries included in the Java Standard Edition API. Packages are denoted by their color.

This pictures illustrates the libraries included in the Java Standard Edition API

How to find the process id of a running Java process on Windows? And how to kill the process alone?

This will work even when there are multiple instance of jar is running

wmic Path win32_process Where "CommandLine Like '%yourname.jar%'" Call Terminate

How to find integer array size in java

public class Test {

    int[] array = { 1, 99, 10000, 84849, 111, 212, 314, 21, 442, 455, 244, 554,
            22, 22, 211 };

    public void Printrange() {

        for (int i = 0; i < array.length; i++) { // <-- use array.length 
            if (array[i] > 100 && array[i] < 500) {
                System.out.println("numbers with in range :" + array[i]);

jQuery CSS Opacity

try using .animate instead of .css or even just on the opacity one and leave .css on the display?? may b

if (jQuery('#nav .drop').animate('display') === 'block') {
    jQuery('#main').animate('opacity') = '0.6';

Android: Difference between Parcelable and Serializable?


Serializable is a markable interface or we can call as an empty interface. It doesn’t have any pre-implemented methods. Serializable is going to convert an object to byte stream. So the user can pass the data between one activity to another activity. The main advantage of serializable is the creation and passing data is very easy but it is a slow process compare to parcelable.


Parcel able is faster than serializable. Parcel able is going to convert object to byte stream and pass the data between two activities. Writing parcel able code is little bit complex compare to serialization. It doesn’t create more temp objects while passing the data between two activities.

Android-java- How to sort a list of objects by a certain value within the object

I have a listview which shows the Information about the all clients I am sorting the clients name using this custom comparator class. They are having some extra lerret apart from english letters which i am managing with this setStrength(Collator.SECONDARY)

 public class CustomNameComparator implements Comparator<ClientInfo> {

    public int compare(ClientInfo o1, ClientInfo o2) { 

        Locale locale=Locale.getDefault();
        Collator collator = Collator.getInstance(locale);
        return, o2.title);


PRIMARY strength: Typically, this is used to denote differences between base characters (for example, "a" < "b"). It is the strongest difference. For example, dictionaries are divided into different sections by base character. 
SECONDARY strength: Accents in the characters are considered secondary differences (for example, "as" < "às" < "at"). Other differences between letters can also be considered secondary differences, depending on the language. A secondary difference is ignored when there is a primary difference anywhere in the strings. 
TERTIARY strength: Upper and lower case differences in characters are distinguished at tertiary strength (for example, "ao" < "Ao" < "aò"). In addition, a variant of a letter differs from the base form on the tertiary strength (such as "A" and "?"). Another example is the difference between large and small Kana. A tertiary difference is ignored when there is a primary or secondary difference anywhere in the strings. 
IDENTICAL strength: When all other strengths are equal, the IDENTICAL strength is used as a tiebreaker. The Unicode code point values of the NFD form of each string are compared, just in case there is no difference. For example, Hebrew cantellation marks are only distinguished at this strength. This strength should be used sparingly, as only code point value differences between two strings are an extremely rare occurrence. Using this strength substantially decreases the performance for both comparison and collation key generation APIs. This strength also increases the size of the collation key. 

**Here is a another way to make a rule base sorting if u need it just sharing**

/*      String rules="< å,Å< ä,Ä< a,A< b,B< c,C< d,D< é< e,E< f,F< g,G< h,H< ï< i,I"+"< j,J< k,K< l,L< m,M< n,N< ö,Ö< o,O< p,P< q,Q< r,R"+"< s,S< t,T< ü< u,U< v,V< w,W< x,X< y,Y< z,Z";
        RuleBasedCollator rbc = null;
        try {
            rbc = new RuleBasedCollator(rules);
        } catch (ParseException e) {
            // TODO Auto-generated catch block
        String myTitles[]={o1.title,o2.title};
        Collections.sort(Arrays.asList(myTitles), rbc);*/

Combining C++ and C - how does #ifdef __cplusplus work?

extern "C" doesn't really change the way that the compiler reads the code. If your code is in a .c file, it will be compiled as C, if it is in a .cpp file, it will be compiled as C++ (unless you do something strange to your configuration).

What extern "C" does is affect linkage. C++ functions, when compiled, have their names mangled -- this is what makes overloading possible. The function name gets modified based on the types and number of parameters, so that two functions with the same name will have different symbol names.

Code inside an extern "C" is still C++ code. There are limitations on what you can do in an extern "C" block, but they're all about linkage. You can't define any new symbols that can't be built with C linkage. That means no classes or templates, for example.

extern "C" blocks nest nicely. There's also extern "C++" if you find yourself hopelessly trapped inside of extern "C" regions, but it isn't such a good idea from a cleanliness perspective.

Now, specifically regarding your numbered questions:

Regarding #1: __cplusplus will stay defined inside of extern "C" blocks. This doesn't matter, though, since the blocks should nest neatly.

Regarding #2: __cplusplus will be defined for any compilation unit that is being run through the C++ compiler. Generally, that means .cpp files and any files being included by that .cpp file. The same .h (or .hh or .hpp or what-have-you) could be interpreted as C or C++ at different times, if different compilation units include them. If you want the prototypes in the .h file to refer to C symbol names, then they must have extern "C" when being interpreted as C++, and they should not have extern "C" when being interpreted as C -- hence the #ifdef __cplusplus checking.

To answer your question #3: functions without prototypes will have C++ linkage if they are in .cpp files and not inside of an extern "C" block. This is fine, though, because if it has no prototype, it can only be called by other functions in the same file, and then you don't generally care what the linkage looks like, because you aren't planning on having that function be called by anything outside the same compilation unit anyway.

For #4, you've got it exactly. If you are including a header for code that has C linkage (such as code that was compiled by a C compiler), then you must extern "C" the header -- that way you will be able to link with the library. (Otherwise, your linker would be looking for functions with names like _Z1hic when you were looking for void h(int, char)

5: This sort of mixing is a common reason to use extern "C", and I don't see anything wrong with doing it this way -- just make sure you understand what you are doing.

Simplest way to detect a mobile device in PHP


//-- Very simple way
$useragent = $_SERVER['HTTP_USER_AGENT']; 
$iPod = stripos($useragent, "iPod"); 
$iPad = stripos($useragent, "iPad"); 
$iPhone = stripos($useragent, "iPhone");
$Android = stripos($useragent, "Android"); 
$iOS = stripos($useragent, "iOS");
//-- You can add billion devices 

$DEVICE = ($iPod||$iPad||$iPhone||$Android||$iOS);

if (!$DEVICE) { ?>

<!-- What you want for all non-mobile devices. Anything with all HTML, PHP, CSS, even full page codes-->

<?php }else{ ?> 

<!-- What you want for all mobile devices. Anything with all HTML, PHP, CSS, even full page codes --> 

<?php } ?>

How to use type: "POST" in jsonp ajax call

If you just want to do a form POST to your own site using $.ajax() (for example, to emulate an AJAX experience), then you can use the jQuery Form Plugin. However, if you need to do a form POST to a different domain, or to your own domain but using a different protocol (a non-secure http: page posting to a secure https: page), then you'll come upon cross-domain scripting restrictions that you won't be able to resolve with jQuery alone (more info). In such cases, you'll need to bring out the big guns: YQL. Put plainly, YQL is a web scraping language with a SQL-like syntax that allows you to query the entire internet as one large table. As it stands now, in my humble opinion YQL is the only [easy] way to go if you want to do cross-domain form POSTing using client-side JavaScript.

More specifically, you'll need to use YQL's Open Data Table containing an Execute block to make this happen. For a good summary on how to do this, you can read the article "Scraping HTML documents that require POST data with YQL". Luckily for us, YQL guru Christian Heilmann has already created an Open Data Table that handles POST data. You can play around with Christian's "htmlpost" table on the YQL Console. Here's a breakdown of the YQL syntax:

  • select * - select all columns, similar to SQL, but in this case the columns are XML elements or JSON objects returned by the query. In the context of scraping web pages, these "columns" generally correspond to HTML elements, so if want to retrieve only the page title, then you would use select head.title.
  • from htmlpost - what table to query; in this case, use the "htmlpost" Open Data Table (you can use your own custom table if this one doesn't suit your needs).
  • url="..." - the form's action URI.
  • postdata="..." - the serialized form data.
  • xpath="..." - the XPath of the nodes you want to include in the response. This acts as the filtering mechanism, so if you want to include only <p> tags then you would use xpath="//p"; to include everything you would use xpath="//*".

Click 'Test' to execute the YQL query. Once you are happy with the results, be sure to (1) click 'JSON' to set the response format to JSON, and (2) uncheck "Diagnostics" to minimize the size of the JSON payload by removing extraneous diagnostics information. The most important bit is the URL at the bottom of the page -- this is the URL you would use in a $.ajax() statement.

Here, I'm going to show you the exact steps to do a cross-domain form POST via a YQL query using this sample form:

<form id="form-post" action="" method="post">
  <input type="text" name="firstname">
  <input type="text" name="lastname">
  <button type="button" onclick="doSubmit()">Add Member</button>

Your JavaScript would look like this:

function doSubmit() {
    url: '//*%20from%20htmlpost%20where%0Aurl%3D%22' +
         encodeURIComponent($('#form-post').attr('action')) + '%22%20%0Aand%20postdata%3D%22' +
         encodeURIComponent($('#form-post').serialize()) +
    dataType: 'json', /* Optional - jQuery autodetects this by default */
    success: function(response) {

The url string is the query URL copied from the YQL Console, except with the form's encoded action URI and serialized input data dynamically inserted.

NOTE: Please be aware of security implications when passing sensitive information over the internet. Ensure the page you are submitting sensitive information from is secure (https:) and using TLS 1.x instead of SSL 3.0.

LaTeX table positioning

What happens if the text plus tables plus text doesn't fit onto a single page? By trying to force the typesetting in this way, you are very likely to end up with pages that run too short; i.e., because a table cannot by default break over a page it will be pushed to the next, and leave a gap on the page before. You'll notice that you never see this in a published book.

The floating behaviour is a Good Thing! I recommend using [htbp] as the default setting for all tables and figures until your document is complete; only then should think about fine-tuning their precise placement.

P.S. Read the FAQ; most other answers here are partial combinations of advice given there.

Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range.

Use a library instead

We don't have to reinvent the wheel. Just use a library to save the time and headache.

js-base64 is good and I confirm it supports unicode very well.

Base64.encode('dankogai');  // ZGFua29nYWk=
Base64.encode('???');    // 5bCP6aO85by+
Base64.encodeURI('???'); // 5bCP6aO85by-

Base64.decode('ZGFua29nYWk=');  // dankogai
Base64.decode('5bCP6aO85by+');  // ???
// note .decodeURI() is unnecessary since it accepts both flavors
Base64.decode('5bCP6aO85by-');  // ???

Converting list to numpy array

If you have a list of lists, you only needed to use ...

import numpy as np
npa = np.asarray(someListOfLists, dtype=np.float32)

per this LINK in the scipy / numpy documentation. You just needed to define dtype inside the call to asarray.

jquery $.each() for objects

Basically you need to do two loops here. The one you are doing already is iterating each element in the 0th array element.

You have programs: [ {...}, {...} ] so programs[0] is { "name":"zonealarm", "price":"500" } So your loop is just going over that.

You could do an outer loop over the array

$.each(data.programs, function(index) {

    // then loop over the object elements
    $.each(data.programs[index], function(key, value) {
        console.log(key + ": " + value);


Set transparent background of an imageview on Android

use RelativeLayout which has 2 imageViews in . and set transparency code on the top imageView.

transparency code :

<solid android:color="@color/white"/>
<gradient android:startColor="#40000000"   android:endColor="#FFFFFFFF" android:angle="270"/>

Java ArrayList of Arrays?

As already answered, you can create an ArrayList of String Arrays as @Péter Török written;

    //Declaration of an ArrayList of String Arrays
    ArrayList<String[]> listOfArrayList = new ArrayList<String[]>();

When assigning different String Arrays to this ArrayList, each String Array's length will be different.

In the following example, 4 different Array of String added, their lengths are varying.

String Array #1: len: 3
String Array #2: len: 1
String Array #3: len: 4
String Array #4: len: 2

The Demonstration code is as below;

import java.util.ArrayList;

public class TestMultiArray {

    public static void main(String[] args) {
        //Declaration of an ArrayList of String Arrays
        ArrayList<String[]> listOfArrayList = new ArrayList<String[]>();

        //Assignment of 4 different String Arrays with different lengths
        listOfArrayList.add( new String[]{"line1: test String 1","line1: test String 2","line1: test String 3"}  );
        listOfArrayList.add( new String[]{"line2: test String 1"}  );
        listOfArrayList.add( new String[]{"line3: test String 1","line3: test String 2","line3: test String 3", "line3: test String 4"}  );
        listOfArrayList.add( new String[]{"line4: test String 1","line4: test String 2"}  );

        // Printing out the ArrayList Contents of String Arrays
        // '$' is used to indicate the String elements of String Arrays
        for( int i = 0; i < listOfArrayList.size(); i++ ) {
            for( int j = 0; j < listOfArrayList.get(i).length; j++ )
                System.out.printf(" $ " + listOfArrayList.get(i)[j]);



And the output is as follows;

 $ line1: test String 1 $ line1: test String 2 $ line1: test String 3
 $ line2: test String 1
 $ line3: test String 1 $ line3: test String 2 $ line3: test String 3 $ line3: test String 4
 $ line4: test String 1 $ line4: test String 2

Also notify that you can initialize a new Array of Sting as below;

new String[]{ str1, str2, str3,... }; // Assuming str's are String objects

So this is same with;

String[] newStringArray = { str1, str2, str3 }; // Assuming str's are String objects

I've written this demonstration just to show that no theArrayList object, all the elements are references to different instantiations of String Arrays, thus the length of each String Arrays are not have to be the same, neither it is important.

One last note: It will be best practice to use the ArrayList within a List interface, instead of which that you've used in your question.

It will be better to use the List interface as below;

    //Declaration of an ArrayList of String Arrays
    List<String[]> listOfArrayList = new ArrayList<String[]>();

How can I list ALL grants a user received?

Assuming you want to list grants on all objects a particular user has received:

select * from all_tab_privs_recd where grantee = 'your user'

This will not return objects owned by the user. If you need those, use all_tab_privs view instead.

How do I make curl ignore the proxy?

My curl was not ignoring the proxy on Ubuntu 12.04 until I set the "no_proxy" (lowercase) environment variable. The --noproxy option was not available.

Remove char at specific index - python

def remove_char(input_string, index):
    first_part = input_string[:index]
    second_part - input_string[index+1:]
    return first_part + second_part

s = 'aababc'
index = 1

zero-based indexing

Best way to check if a character array is empty

if (text[0] == '\0')
    /* Code... */

Use this if you're coding for micro-controllers with little space on flash and/or RAM. You will waste a lot more flash using strlen than checking the first byte.

The above example is the fastest and less computation is required.

can't start MySql in Mac OS 10.6 Snow Leopard

my apple processor version10.6.3 is error and i can click system preference

Using scp to copy a file to Amazon EC2 instance?

I had exactly same problem, my solution was to

scp -i /path/pem -r /path/file/ ec2-user@public aws dns name: (leave it blank here)

once you done this part, get into ssh server and mv file to desired location

How can I symlink a file in Linux?

How to create symlink in vagrant. Steps:

  1. In vagrant file create a synced folder. e.g config.vm.synced_folder "F:/Sunburst/source/sunburst/lms", "/source" F:/Sunburst/source/sunburst/lms :- where the source code, /source :- directory path inside the vagrant
  2. Vagrant up and type vagrant ssh and go to source directory e.g cd source
  3. Verify your source code folder structure is available in the source directory. e.g /source/local
  4. Then go to the guest machine directory where the files which are associate with the browser. After get backup of the file. e.g sudo mv local local_bk
  5. Then create symlink e.g sudo ln -s /source/local local. local mean link-name (folder name in guest machine which you are going to link) if you need to remove the symlink :- Type sudo rm local

Fatal error: Out of memory, but I do have plenty of memory (PHP)

Could be an issue with MySQL and the number of open connections, hence why it sorts itself out when you restart every few days. Are they auto closing on script shutdown?

sequelize findAll sort order in nodejs

If you are using MySQL, you can use order by FIELD(id, ...) approach:

    where: {id : {$in : companyIds}},
    order: sequelize.literal("FIELD(,"+companyIds.join(',')+")")

Keep in mind, it might be slow. But should be faster, than manual sorting with JS.

Number input type that takes only integers?

<input type="text" name="PhoneNumber" pattern="[0-9]{10}" title="Phone number">

Using this code, the input to the text field limits to enter only digits. Pattern is the new attribute available in HTML 5.

Pattern attribute doc

Selecting rows where remainder (modulo) is 1 after division by 2?

select * from table where value % 2 = 1 works fine in mysql.

Finding the position of bottom of a div with jquery

EDIT: this solution is now in the original answer too.

The accepted answer is not quite correct. You should not be using the position() function since it is relative to the parent. If you are doing global positioning(in most cases?) you should only add the offset top with the outerheight like so:

var actualBottom = $(selector).offset().top + $(selector).outerHeight(true);

The docs

What are the differences between Visual Studio Code and Visual Studio?

Visual Studio Code is an editor while Visual Studio is an IDE.

Visual Studio Code is cross-platform and fast, while Visual Studio is not fast.

Note that Visual Studio for Mac is available now but is a different product compared to Visual Studio (Windows). It's based on Xamarin Studio and lacks support for some older .NET project types. It does successfully build solutions created in Visual Studio 2017. Visual Studio for Mac has a more limited UI (for example, no customizable toolbar). So for cross-platform work, Visual Studio Code may still be preferable.

javascript password generator

If you have lodash >= 4.0 in place there is a more elegant way of doing it

var chars = 'abcdefghkmnpqrstuvwxyz23456789';
function generatePassword(length) {
  return _.sampleSize(chars, length).join('');

Difference between npx and npm?

Simple Definition:

npm - Javascript package manager

npx - Execute npm package binaries

jQuery: How can I create a simple overlay?

Here is a simple javascript only solution

function displayOverlay(text) {
    $("<table id='overlay'><tbody><tr><td>" + text + "</td></tr></tbody></table>").css({
        "position": "fixed",
        "top": 0,
        "left": 0,
        "width": "100%",
        "height": "100%",
        "background-color": "rgba(0,0,0,.5)",
        "z-index": 10000,
        "vertical-align": "middle",
        "text-align": "center",
        "color": "#fff",
        "font-size": "30px",
        "font-weight": "bold",
        "cursor": "wait"

function removeOverlay() {



How to check null objects in jQuery

if ( $('#whatever')[0] ) {...}

The jQuery object which is returned by all native jQuery methods is NOT an array, it is an object with many properties; one of them being a "length" property. You can also check for size() or get(0) or get() - 'get(0)' works the same as accessing the first element, i.e. $(elem)[0]

Passing variables in remote ssh command

If you use

ssh [email protected] "~/tools/ $BUILD_NUMBER"

instead of

ssh [email protected] '~/tools/ $BUILD_NUMBER'

your shell will interpolate the $BUILD_NUMBER before sending the command string to the remote host.

java.lang.ClassNotFoundException: org.springframework.web.context.ContextLoaderListener

For me the fix was to right click on my webapp module > Maven > Update Project

Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured

Excluding the DataSourceAutoConfiguration.class worked for me:

@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class })

How can I prevent the TypeError: list indices must be integers, not tuple when copying a python list to a numpy array?

Just if someone is having this issue and hadn't done list[index, sub-index], you could be having the problem because you're missing a comma between two arrays in an array of arrays (It happened to me).

What's the difference between fill_parent and wrap_content?

fill_parent :

A component is arranged layout for the fill_parent will be mandatory to expand to fill the layout unit members, as much as possible in the space. This is consistent with the dockstyle property of the Windows control. A top set layout or control to fill_parent will force it to take up the entire screen.


Set up a view of the size of wrap_content will be forced to view is expanded to show all the content. The TextView and ImageView controls, for example, is set to wrap_content will display its entire internal text and image. Layout elements will change the size according to the content. Set up a view of the size of Autosize attribute wrap_content roughly equivalent to set a Windows control for True.

For details Please Check out this link :

How do I set response headers in Flask?

We can set the response headers in Python Flask application using Flask application context using flask.g

This way of setting response headers in Flask application context using flask.g is thread safe and can be used to set custom & dynamic attributes from any file of application, this is especially helpful if we are setting custom/dynamic response headers from any helper class, that can also be accessed from any other file ( say like middleware, etc), this flask.g is global & valid for that request thread only.

Say if i want to read the response header from another api/http call that is being called from this app, and then extract any & set it as response headers for this app.

Sample Code: file:

import flask
from flask import request, g
from multidict import CIMultiDict
from asyncio import TimeoutError as HttpTimeout
from aiohttp import ClientSession

    def _extract_response_header(response)
      extracts response headers from response object 
      and stores that required response header in flask.g app context
      headers = CIMultiDict(response.headers)
      if 'my_response_header' not in g:
        g.my_response_header= {}
        g.my_response_header['x-custom-header'] = headers['x-custom-header']

    async def call_post_api(post_body):
      sample method to make post api call using aiohttp clientsession
        async with ClientSession() as session:
          async with, headers=_headers, json=post_body) as response:
            responseResult = await
            _extract_headers(response, responseResult)
            response_text = await response.text()
      except (HttpTimeout, ConnectionError) as ex:
        raise HttpTimeout(exception_message)


import flask
from flask import request, g

class SimpleMiddleWare(object):
    Simple WSGI middleware

    def __init__(self, app): = app
        self._header_name = "any_request_header"

    def __call__(self, environ, start_response):
        middleware to capture request header from incoming http request
        request_id_header = environ.get(self._header_name)
        environ[self._header_name] = request_id_header

        def new_start_response(status, response_headers, exc_info=None):
            set custom response headers
            # set the request header as response header
            response_headers.append((self._header_name, request_id_header))
            # this is trying to access flask.g values set in helper class & set that as response header
            values = g.get(my_response_header, {})
            if values.get('x-custom-header'):
                response_headers.append(('x-custom-header', values.get('x-custom-header')))
            return start_response(status, response_headers, exc_info)

        return, new_start_response)

Calling the middleware from main class

file :

from flask import Flask
import asyncio
from gevent.pywsgi import WSGIServer
from middleware import SimpleMiddleWare

    app = Flask(__name__)
    app.wsgi_app = SimpleMiddleWare(app.wsgi_app)

PostgreSQL Autoincrement

If you want to add sequence to id in the table which already exist you can use:

CREATE SEQUENCE user_id_seq;
ALTER TABLE user ALTER user_id SET DEFAULT NEXTVAL('user_id_seq');

How to call getResources() from a class which has no context?

Example: Getting app_name string:

Resources.getSystem().getString( R.string.app_name )

How does numpy.histogram() work?

Another useful thing to do with numpy.histogram is to plot the output as the x and y coordinates on a linegraph. For example:

arr = np.random.randint(1, 51, 500)
y, x = np.histogram(arr, bins=np.arange(51))
fig, ax = plt.subplots()
ax.plot(x[:-1], y)

enter image description here

This can be a useful way to visualize histograms where you would like a higher level of granularity without bars everywhere. Very useful in image histograms for identifying extreme pixel values.

How to edit data in result grid in SQL Server Management Studio

You can do something similar to what you want. Right click on a table and select "edit top 200 rows" (if you are on SQL Server 2008) or "open table" in SQL Server 2005. Once you get there, there is a button on the top that says "SQL"; when you click on it, it lets you write an SQL statement and you can edit the results of it if you click a cell you want to change.

How to match letters only using java regex, matches method?

import java.util.regex.*;

/* Write an application that prompts the user for a String that contains at least
 * five letters and at least five digits. Continuously re-prompt the user until a
 * valid String is entered. Display a message indicating whether the user was
 * successful or did not enter enough digits, letters, or both.
public class FiveLettersAndDigits {

  private static String readIn() { // read input from stdin
    StringBuilder sb = new StringBuilder();
    int c = 0;
    try { // do not use try-with-resources. We don't want to close the stdin stream
      BufferedReader reader = new BufferedReader(new InputStreamReader(;
      while ((c = != 0) { // read all characters until null
        // We don't want new lines, although we must consume them.
        if (c != 13 && c != 10) {
          sb.append((char) c);
        } else {
          break; // break on new line (or else the loop won't terminate)
      // reader.readLine(); // get the trailing new line
    } catch (IOException ex) {
      System.err.println("Failed to read user input!");

    return sb.toString().trim();

   * Check the given input against a pattern
   * @return the number of matches
  private static int getitemCount(String input, String pattern) {
    int count = 0;

    try {
      Pattern p = Pattern.compile(pattern);
      Matcher m = p.matcher(input);
      while (m.find()) { // count the number of times the pattern matches
    } catch (PatternSyntaxException ex) {
      System.err.println("Failed to test input String \"" + input + "\" for matches to pattern \"" + pattern + "\"!");

    return count;

  private static String reprompt() {
    System.out.print("Entered input is invalid! Please enter five letters and five digits in any order: ");

    String in = readIn();

    return in;

  public static void main(String[] args) {
    int letters = 0, digits = 0;
    String in = null;
    System.out.print("Please enter five letters and five digits in any order: ");
    in = readIn();
    while (letters < 5 || digits < 5) { // will keep occuring until the user enters sufficient input
      if (null != in && in.length() > 9) { // must be at least 10 chars long in order to contain both
        // count the letters and numbers. If there are enough, this loop won't happen again.
        letters = getitemCount(in, "[A-Za-z]");
        digits = getitemCount(in, "[0-9]");

        if (letters < 5 || digits < 5) {
          in = reprompt(); // reset in case we need to go around again.
      } else {
        in = reprompt();


UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 7: ordinal not in range(128)

You need to encode Unicode explicitly before writing to a file, otherwise Python does it for you with the default ASCII codec.

Pick an encoding and stick with it:

f.write(printinfo.encode('utf8') + '\n')

or use to create a file object that'll encode for you as you write to the file:

import io

f =, 'w', encoding='utf8')

You may want to read:

before continuing.

how to show confirmation alert with three buttons 'Yes' 'No' and 'Cancel' as it shows in MS Word

This cannot be done with the native javascript dialog box, but a lot of javascript libraries include more flexible dialogs. You can use something like jQuery UI's dialog box for this.

See also these very similar questions:

Here's an example, as demonstrated in this jsFiddle:

    <script type="text/javascript" src=""></script>
    <script type="text/javascript" src=""></script>
    <link rel="stylesheet" type="text/css" href="/css/normalize.css">
    <link rel="stylesheet" type="text/css" href="/css/result-light.css">
    <link rel="stylesheet" type="text/css" href="">
    <a class="checked" href="">Click here</a>
    <script type="text/javascript">

        $(function() {
            $('.checked').click(function(e) {
                var dialog = $('<p>Are you sure?</p>').dialog({
                    buttons: {
                        "Yes": function() {alert('you chose yes');},
                        "No":  function() {alert('you chose no');},
                        "Cancel":  function() {
                            alert('you chose cancel');


Do Facebook Oauth 2.0 Access Tokens Expire?

check the following things when you interact with facebook graph api.

1) Application connect URL should be the base of your "redirect_uri" connect URL:- redirect_uri - 2) Your "redirect_uri" should be same in the both case (when you request for a verification code and request for an access_token) redirect_uri - 3) you should encode the the argument when you request for an access_token 4) shouldn't pass the argument (type=client_cred) when you request for an access_token. the authorization server will issue a token without session part. we can't use this token with "me" alias in graph api. This token will have length of (40) but a token with session part will have a length of(81). An access token without session part will work with some cases

eg: -|EyWJJYqrdgQgV1bfueck320z7MM. But Graph API with "me" alias will work with only token with session part.

How do I fix the npm UNMET PEER DEPENDENCY warning?

The given answer wont always work. If it does not fix your issue. Make sure that you are also using the correct symbol in your package.json. This is very important to fix that headache. For example:

warning " > @angular/[email protected]" has incorrect peer dependency "typescript@>=2.4.2 <2.7".
warning " > [email protected]" has incorrect peer dependency "typescript@>=2.4.2 <2.6".

So my typescript needs to be between 2.4.2 and 2.6 right?

So I changed my typescript library from using "typescript": "^2.7" to using "typescript": "^2.5". Seems correct?


The ^ means that you are okay with npm using "typescript": "2.5" or "2.6" or "2.7" etc...

If you want to learn what the ^ and ~ it mean see: What's the difference between tilde(~) and caret(^) in package.json?

Also you have to make sure that the package exists. Maybe there is no "typescript": "2.5.9" look up the package numbers. To be really safe just remove the ~ or the ^ if you dont want to read what they mean.

How do I force Maven to use my local repository rather than going out to remote repos to retrieve artifacts?

Even when considering all answers above you might still run into issues that will terminate your maven offline build with an error. Especially, you may experience a warning as follwos:

[WARNING] The POM for org.apache.maven.plugins:maven-resources-plugin:jar:2.6 is missing, no dependency information available

The warning will be immediately followed by further errors and maven will terminate.

For us the safest way to build offline with a maven offline cache created following the hints above is to use following maven offline parameters:

mvn -o -llr -Dmaven.repo.local=<path_to_your_offline_cache> ...

Especially, option -llr prevents you from having to tune your local cache as proposed in answer #4.

Also take care that that the localRepository parameter in settings.xml is set as follows:


Correct way to select from two tables in SQL Server with no common field to join on

Cross join will help to join multiple tables with no common fields.But be careful while joining as this join will give cartesian resultset of two tables. QUERY:

 , table2,columnA
FROM table1 

Alternative way to join on some condition that is always true like

 , table2,columnA
FROM table1 
INNER JOIN table2 ON 1=1

But this type of query should be avoided for performance as well as coding standards.

How do I get the RootViewController from a pushed controller?

Use the viewControllers property of the UINavigationController. Example code:

// Inside another ViewController
NSArray *viewControllers = self.navigationController.viewControllers;
UIViewController *rootViewController = [viewControllers objectAtIndex:viewControllers.count - 2];

This is the standard way of getting the "back" view controller. The reason objectAtIndex:0 works is because the view controller you're trying to access is also the root one, if you were deeper in the navigation, the back view would not be the same as the root view.

AngularJS passing data to $http.get request

Solution for those who are interested in sending params and headers in GET request

$http.get('', {
        params:  {page: 1, limit: 100, sort: 'name', direction: 'desc'},
        headers: {'Authorization': 'Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ=='}
.then(function(response) {
    // Request completed successfully
}, function(x) {
    // Request error

Complete service example will look like this

var mainApp = angular.module("mainApp", []);

mainApp.service('UserService', function($http, $q){

   this.getUsers = function(page = 1, limit = 100, sort = 'id', direction = 'desc') {

        var dfrd = $q.defer();
                params:{page: page, limit: limit, sort: sort, direction: direction},
                headers: {Authorization: 'Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ=='}
        .then(function(response) {
            if ( == true ) { 

            } else {

        }, function(x) {

        return dfrd.promise;


Copy or rsync command

The command as written will create new directories and files with the current date and time stamp, and yourself as the owner. If you are the only user on your system and you are doing this daily it may not matter much. But if preserving those attributes matters to you, you can modify your command with

cp -pur /home/abc/* /mnt/windowsabc/

The -p will preserve ownership, timestamps, and mode of the file. This can be pretty important depending on what you're backing up.

The alternative command with rsync would be

rsync -avh /home/abc/* /mnt/windowsabc

With rsync, -a indicates "archive" which preserves all those attributes mentioned above. -v indicates "verbose" which just lists what it's doing with each file as it runs. -z is left out here for local copies, but is for compression, which will help if you are backing up over a network. Finally, the -h tells rsync to report sizes in human-readable formats like MB,GB,etc.

Out of curiosity, I ran one copy to prime the system and avoid biasing against the first run, then I timed the following on a test run of 1GB of files from an internal SSD drive to a USB-connected HDD. These simply copied to empty target directories.

cp -pur    : 19.5 seconds
rsync -ah  : 19.6 seconds
rsync -azh : 61.5 seconds

Both commands seem to be about the same, although zipping and unzipping obviously tax the system where bandwidth is not a bottleneck.

Sublime Text 2 Code Formatting

A similar option in Sublime Text is the built in Edit->Line->Reindent. You can put this code in Preferences -> Key Bindings User:

{ "keys": ["alt+shift+f"], "command": "reindent"} 

I use alt+shift+f because I'm a Netbeans user.

To format your code, select all by pressing ctrl+a and "your key combination". Excuse me for my bad english.

Or if you don't want to select all before formatting, add an argument to the command instead:

{ "keys": ["alt+shift+f"], "command": "reindent", "args": {"single_line": false} }

(as per comment by @Supr below)

How can I read and parse CSV files in C++?

You might want to look at my FOSS project CSVfix (updated link), which is a CSV stream editor written in C++. The CSV parser is no prize, but does the job and the whole package may do what you need without you writing any code.

See alib/src/a_csv.cpp for the CSV parser, and csvlib/src/csved_ioman.cpp (IOManager::ReadCSV) for a usage example.

Jquery - How to make $.post() use contentType=application/json?

I know this is a late answer, I actually have a shortcut method that I use for posting/reading to/from MS based services.. it works with MVC as well as ASMX etc...


  ,{}  /*empty object for nothing, or object to send as Application/JSON */
  ,function(data,jqXHR) {
    //use the data from the response.
  ,function(err,jqXHR) {
    //additional error handling.
//sends a json request to an ASMX or WCF service configured to reply to JSON requests.
(function ($) {
  var tries = 0; //IE9 seems to error out the first ajax call sometimes... will retry up to 5 times

  $.msajax = function (url, data, onSuccess, onError) {
    return $.ajax({
      'type': "POST"
      , 'url': url
      , 'contentType': "application/json"
      , 'dataType': "json"
      , 'data': typeof data == "string" ? data : JSON.stringify(data || {})
      ,beforeSend: function(jqXHR) {
      , 'complete': function(jqXHR, textStatus) {
        handleResponse(jqXHR, textStatus, onSuccess, onError, function(){
            $.msajax(url, data, onSuccess, onError);
          }, 100 * tries); //try again

  $.msajax.defaultErrorMessage = "Error retreiving data.";

  function logError(err, errorHandler, jqXHR) {
    tries = 0; //reset counter - handling error response

    //normalize error message
    if (typeof err == "string") err = { 'Message': err };

    if (console && console.debug && console.dir) {
      console.debug("ERROR processing jQuery.msajax request.");
      console.dir({ 'details': { 'error': err, 'jqXHR':jqXHR } });

    try {
      errorHandler(err, jqXHR);
    } catch (e) {}

  function handleResponse(jqXHR, textStatus, onSuccess, onError, onRetry) {
    var ret = null;
    var reterr = null;
    try {
      //error from jqXHR
      if (textStatus == "error") {
        var errmsg = $.msajax.defaultErrorMessage || "Error retreiving data.";

        //check for error response from the server
        if (jqXHR.status >= 300 && jqXHR.status < 600) {
          return logError( jqXHR.statusText || msg, onError, jqXHR);

        if (tries++ < 5) return onRetry();

        return logError( msg, onError, jqXHR);

      //not an error response, reset try counter
      tries = 0;

      //check for a redirect from server (usually authentication token expiration).
      if (jqXHR.responseText.indexOf("|pageRedirect||") > 0) {
        location.href = decodeURIComponent(jqXHR.responseText.split("|pageRedirect||")[1].split("|")[0]).split('?')[0];

      //parse response using ajax enabled parser (if available)
      ret = ((JSON && JSON.parseAjax) || $.parseJSON)(jqXHR.responseText);

      //invalid response
      if (!ret) throw jqXHR.responseText;  

      // d property wrap as of .Net 3.5
      if (ret.d) ret = ret.d;

      //has an error
      reterr = (ret && (ret.error || ret.Error)) || null; //specifically returned an "error"

      if (ret && ret.ExceptionType) { //Microsoft Webservice Exception Response
        reterr = ret

    } catch (err) {
      reterr = {
        'Message': $.msajax.defaultErrorMessage || "Error retreiving data."
        ,'debug': err

    //perform final logic outside try/catch, was catching error in onSuccess/onError callbacks
    if (reterr) {
      logError(reterr, onError, jqXHR);

    onSuccess(ret, jqXHR);

} (jQuery));

NOTE: I also have a JSON.parseAjax method that is modified from's JS file, that adds handling for the MS "/Date(...)/" dates...

The modified json2.js file isn't included, it uses the script based parser in the case of IE8, as there are instances where the native parser breaks when you extend the prototype of array and/or object, etc.

I've been considering revamping this code to implement the promises interfaces, but it's worked really well for me.

Unfortunately MyApp has stopped. How can I solve this?

Use the LogCat and try to find what is causing the app to crash.

To see Logcat if you use Android Studio then Press ALT + 6 or

if you use Eclipse then Window -> Open Perspective -> Other - LogCat

Go to the LogCat, from the drop down menu select error. This will contain all the required information to help you debug. If that doesn't help, post the LogCat as an edit to your question and somebody will help you out.

Docker Error bind: address already in use

Just a side note if you have the same issue and is with Windows:

In my case the process in my way is just grafana-server.exe. Because I first downloaded the binary version and double click the executable, and it now starts as a service by user SYSTEM which I cannot taskkill (no permission)

I have to go to "Service manager" of Windows and search for service "Grafana", and stop it. After that port 3000 is no longer occupied.

Hope that helps.

remove kernel on jupyter notebook

In jupyter notebook run:

!echo y | jupyter kernelspec uninstall unwanted-kernel 

In anaconda prompt run:

jupyter kernelspec uninstall unwanted-kernel

How to get list of all installed packages along with version in composer?

You can run composer show -i (short for --installed).

In the latest version just use composer show.

The -i options has been deprecated.

You can also use the global instalation of composer: composer global show

Generating random numbers in C

#include <stdlib.h>

int main()
    int x;
    x = rand(6);
    printf("%d", x);

Especially as a beginner, you should ask your compiler to print every warning about bad code that it can generate. Modern compilers know lots of different warnings which help you to program better. For example, when you compile this program with the GNU C Compiler:

$ gcc -W -Wall rand.c
rand.c: In function `main':
rand.c:5: error: too many arguments to function `rand'
rand.c:6: warning: implicit declaration of function `printf'

You get two warnings here. The first one says that the rand function only takes zero arguments, not one as you tried. To get a random number between 0 and n, you can use the expression rand() % n, which is not perfect but ok for small n. The resulting random numbers are normally not evenly distributed; smaller values are returned more often.

The second warning tells you that you are calling a function that the compiler doesn't know at that point. You have to tell the compiler by saying #include <stdio.h>. Which include files are needed for which functions is not always simple, but asking the Open Group specification for portable operating systems works in many cases:

These two warnings tell you much about the history of the C programming language. 40 years back, the definition of a function didn't include the number of parameters or the types of the parameters. It was also ok to call an unknown function, which in most cases worked. If you want to write code today, you should not rely on these old features but instead enable your compiler's warnings, understand the warnings and then fix them properly.

How can I make a Python script standalone executable to run without ANY dependency?

I'm told that PyRun is also an option. It currently supports Linux, FreeBSD and Mac OS X.

The endpoint reference (EPR) for the Operation not found is

Open WSDL file and find:

<soap:operation soapAction="[actionNameIsHere]" style="document"/>

Add to the requests header [request send to service]:

'soapAction' : '[actionNameIsHere]'

This work for me.

For devs. using node-soap [ ] - example:

var soap = require('soap');
var options = {
   ...your options...
   forceSoap12Headers: true
        wsdl, options,
            function(err, client) {
                if(err) {
                    return callBack(err, result);
                client.addHttpHeader('soapAction', '[actionNameIsHere]');
                ...your code - request send...

MySQL timestamp select date range

Usually it would be this:

  FROM yourtable
 WHERE yourtimetimefield>='2010-10-01'
   AND yourtimetimefield< '2010-11-01'

But because you have a unix timestamps, you'll need something like this:

  FROM yourtable
 WHERE yourtimetimefield>=unix_timestamp('2010-10-01')
   AND yourtimetimefield< unix_timestamp('2010-11-01')

Oracle SqlPlus - saving output in a file but don't show on screen

Try This:

sqlplus -s ${ORA_CONN_STR} <<EOF >/dev/null

Avoiding "resource is out of sync with the filesystem"

A little hint. The message often appears during rename operation. The quick workaround for me is pressing Ctrl-Y (redo shortcut) after message confirmation. It works only if the renaming affects a single file.

Use curly braces to initialize a Set in Python

Compare also the difference between {} and set() with a single word argument.

>>> a = set('aardvark')
>>> a
{'d', 'v', 'a', 'r', 'k'} 
>>> b = {'aardvark'}
>>> b

but both a and b are sets of course.

PhoneGap Eclipse Issue - eglCodecCommon glUtilsParamSize: unknow param errors

I Get the same message, when using Intel XHAM emulator (instead of ARM) and have "Use Host GPU" option enabled. I belive when you disable it, it goes away.

Android intent for playing video?

I have come across this with the Hero, using what I thought was a published API. In the end, I used a test to see if the intent could be received:

private boolean isCallable(Intent intent) {
    List<ResolveInfo> list = getPackageManager().queryIntentActivities(intent, 
    return list.size() > 0;

In use when I would usually just start the activity:

final Intent intent = new Intent("");
intent.setClassName("", "");
if (isCallable(intent)) {
    // call the intent as you intended.
} else {
    // make alternative arrangements.

obvious: If you go down this route - using non-public APIs - you must absolutely provide a fallback which you know definitely works. It doesn't have to be perfect, it can be a Toast saying that this is unsupported for this handset/device, but you should avoid an uncaught exception. end obvious.

I find the Open Intents Registry of Intents Protocols quite useful, but I haven't found the equivalent of a TCK type list of intents which absolutely must be supported, and examples of what apps do different handsets.

Convert a bitmap into a byte array

Use a MemoryStream instead of a FileStream, like this:

MemoryStream ms = new MemoryStream();
bmp.Save (ms, ImageFormat.Jpeg);
byte[] bmpBytes = ms.ToArray();

Converting double to string with N decimals, dot as decimal separator, and no thousand separator

double value = 3.14159D;
string v = value.ToString().Replace(",", ".");

Output: 3.14159

SQL query for a carriage return in a string and ultimately removing carriage return

You can also use regular expressions:

SELECT * FROM Parameters WHERE Name REGEXP '\n';

How do I auto-submit an upload form when a file is selected?

Just tell the file-input to automatically submit the form on any change:

<form action="">_x000D_
    <input type="file" onchange="form.submit()" />_x000D_

This solution works like this:

  • onchange makes the input element execute the following script, whenever the value is modified
  • form references the form, that this input element is part of
  • submit() causes the form to send all data to the URL, as specified in action

Advantages of this solution:

  • Works without ids. It makes life easier, if you have several forms in one html page.
  • Native javascript, no jQuery or similar required.
  • The code is inside the html-tags. If you inspect the html, you will see it's behavior right away.

Using both Python 2.x and Python 3.x in IPython Notebook

Under Windows 7 I had anaconda and anaconda3 installed. I went into \Users\me\anaconda\Scripts and executed

sudo .\ipython kernelspec install-self

then I went into \Users\me\anaconda3\Scripts and executed

sudo .\ipython kernel install

(I got jupyter kernelspec install-self is DEPRECATED as of 4.0. You probably want 'ipython kernel install' to install the IPython kernelspec.)

After starting jupyter notebook (in anaconda3) I got a neat dropdown menu in the upper right corner under "New" letting me choose between Python 2 odr Python 3 kernels.

How to sort findAll Doctrine's method?

You need to use a criteria, for example:


namespace Bundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;
use Doctrine\Common\Collections\Criteria;

* Thing controller
class ThingController extends Controller
    public function thingsAction(Request $request, $id)
        $criteria = new Criteria(null, <<DQL ordering expression>>, null, null );

        $rep    = $this->getDoctrine()->getManager()->getRepository('Bundle:Thing');
        $things = $rep->matching($criteria);
        return $this->render('Bundle:Thing:things.html.twig', [
            'entities' => $things,

"Parse Error : There is a problem parsing the package" while installing Android application

One reason could be, that your activity'name is not defined in the manifest


above code was creating the same issue with me

memcpy() vs memmove()

The memory in memcpy cannot overlap or you risk undefined behaviour, while the memory in memmove can overlap.

char a[16];
char b[16];

memcpy(a,b,16);           // valid
memmove(a,b,16);          // Also valid, but slower than memcpy.
memcpy(&a[0], &a[1],10);  // Not valid since it overlaps.
memmove(&a[0], &a[1],10); // valid. 

Some implementations of memcpy might still work for overlapping inputs but you cannot count of that behaviour. While memmove must allow for overlapping.

How to check if a row exists in MySQL? (i.e. check if an email exists in MySQL)

You have to execute your query and add single quote to $email in the query beacuse it's a string, and remove the is_resource($query) $query is a string, the $result will be the resource

$query = "SELECT `email` FROM `tblUser` WHERE `email` = '$email'";
$result = mysqli_query($link,$query); //$link is the connection

if(mysqli_num_rows($result) > 0 ){....}


Base in your edit just change:

if(is_resource($query) && mysqli_num_rows($query) > 0 ){
        $query = mysqli_fetch_assoc($query);
        echo $email . " email exists " .  $query["email"] . "\n";


if(is_resource($result) && mysqli_num_rows($result) == 1 ){
        $row = mysqli_fetch_assoc($result);
         echo $email . " email exists " .  $row["email"] . "\n";

and you will be fine


A better way should be have a Store Procedure that execute the following SQL passing the Email as Parameter

                  SELECT *
                  FROM `Table`
                  WHERE `email` = @Email)
          , 1, 0) as `Exist`

and retrieve the value in php


 $query = Call MYSQL_SP($EMAIL);
 $result = mysqli_query($conn,$query);
 $row = mysqli_fetch_array($result)
 $exist = ($row['Exist']==1)? 'the email exist' : 'the email doesnt exist';

How to retrieve field names from temporary table (SQL Server 2008)

select * from tempdb.sys.columns where object_id =

How do I clone a Django model instance object and save it to the database?

setting pk to None is better, sinse Django can correctly create a pk for you

object_copy = MyObject.objects.get(pk=...) = None

Plotting of 1-dimensional Gaussian distribution function

The correct form, based on the original syntax, and correctly normalized is:

def gaussian(x, mu, sig):
    return 1./(np.sqrt(2.*np.pi)*sig)*np.exp(-np.power((x - mu)/sig, 2.)/2)

Disable SSL fallback and use only TLS for outbound connections in .NET? (Poodle mitigation)

We are doing the same thing. To support only TLS 1.2 and no SSL protocols, you can do this:

System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

SecurityProtocolType.Tls is only TLS 1.0, not all TLS versions.

As a side: If you want to check that your site does not allow SSL connections, you can do so here (I don't think this will be affected by the above setting, we had to edit the registry to force IIS to use TLS for incoming connections):

To disable SSL 2.0 and 3.0 in IIS, see this page:

setting request headers in selenium

Had the same issue today, except that I needed to set different referer per test. I ended up using a middleware and a class to pass headers to it. Thought I'd share (or maybe there's a cleaner solution?):


class CustomHeadersHelper
  cattr_accessor :headers

class RequestHeaders
  def initialize(app, helper = nil)
    @app, @helper = app, helper

  def call(env)
    if @helper
      headers = @helper.headers

      if headers.is_a?(Hash)
        headers.each do |k,v|
          env["HTTP_#{k.upcase.gsub("-", "_")}"] = v


require 'request_headers'

if %w(test cucumber).include?(Rails.env)
  Rails.application.config.middleware.insert_before Rack::Lock, "RequestHeaders", CustomHeadersHelper


require 'request_headers'

module CapybaraHeaderHelpers
  shared_context "navigating within the site" do
    before(:each) { add_headers("Referer" => Capybara.app_host + "/") }

  def add_headers(custom_headers)
    if Capybara.current_driver == :rack_test
      custom_headers.each do |name, value|
        page.driver.browser.header(name, value)
      CustomHeadersHelper.headers = custom_headers


config.include CapybaraHeaderHelpers

Then I can include the shared context wherever I need, or pass different headers in another before block. I haven't tested it with anything other than Selenium and RackTest, but it should be transparent, as header injection is done before the request actually hits the application.

getFilesDir() vs Environment.getDataDirectory()

Try this


rails 3.1.0 ActionView::Template::Error (application.css isn't precompiled)

For all those who are reading this but do not have problem with application.css and instead with their custom CSS classes e.g. admin.css, base.css etc.

Solution is to use as mentioned

bundle exec rake assets:precompile

And in stylesheets references just reference application.css

<%= stylesheet_link_tag    "application", :media => "all" %>

Since assets pipeline will precompile all of your stylesheets in application.css. This also happens in development so using any other references is wrong when using assets pipeline.

SQLSTATE[HY000] [1045] Access denied for user 'root'@'localhost' (using password: YES) symfony2

I'm Using Xampp and Laravel 5.8 in Windows 10, and i've been like this before. When i got this problem, My XAMPP is no have Password Then I tried to delete some codes in config>database.php

'password' => env('DB_PASSWORD', ''),

And in .env


the Problem is solved

How to list files in a directory in a C program?

Here is a complete program how to recursively list folder's contents:

#include <dirent.h> 
#include <stdio.h> 
#include <string.h>

#define NORMAL_COLOR  "\x1B[0m"
#define GREEN  "\x1B[32m"
#define BLUE  "\x1B[34m"

/* let us make a recursive function to print the content of a given folder */

void show_dir_content(char * path)
  DIR * d = opendir(path); // open the path
  if(d==NULL) return; // if was not able return
  struct dirent * dir; // for the directory entries
  while ((dir = readdir(d)) != NULL) // if we were able to read somehting from the directory
      if(dir-> d_type != DT_DIR) // if the type is not directory just print it with blue
        printf("%s%s\n",BLUE, dir->d_name);
      if(dir -> d_type == DT_DIR && strcmp(dir->d_name,".")!=0 && strcmp(dir->d_name,"..")!=0 ) // if it is a directory
        printf("%s%s\n",GREEN, dir->d_name); // print its name in green
        char d_path[255]; // here I am using sprintf which is safer than strcat
        sprintf(d_path, "%s/%s", path, dir->d_name);
        show_dir_content(d_path); // recall with the new path
    closedir(d); // finally close the directory

int main(int argc, char **argv)

  printf("%s\n", NORMAL_COLOR);


  printf("%s\n", NORMAL_COLOR);

How to skip to next iteration in jQuery.each() util?

Javascript sort of has the idea of 'truthiness' and 'falsiness'. If a variable has a value then, generally 9as you will see) it has 'truthiness' - null, or no value tends to 'falsiness'. The snippets below might help:

var temp1; 
if ( temp1 )...  // false

var temp2 = true;
if ( temp2 )...  // true

var temp3 = "";
if ( temp3 ).... // false

var temp4 = "hello world";
if ( temp4 )...  // true

Hopefully that helps?

Also, its worth checking out these videos from Douglas Crockford

update: thanks @cphpython for spotting the broken links - I've updated to point at working versions now

The Javascript language

Javascript - The Good Parts

#ifdef replacement in the Swift language

This builds on Jon Willis's answer that relies upon assert, which only gets executed in Debug compilations:

func Log(_ str: String) { 
func DebugLog(_ str: String) -> Bool { 
    return true

My use case is for logging print statements. Here is a benchmark for Release version on iPhone X:

let iterations = 100_000_000
let time1 = CFAbsoluteTimeGetCurrent()
for i in 0 ..< iterations {
    Log ("? unarchiveArray:\(fileName) memoryTime:\(memoryTime) count:\(array.count)")
var time2 = CFAbsoluteTimeGetCurrent()
print ("Log: \(time2-time1)" )


Log: 0.0

Looks like Swift 4 completely eliminates the function call.

Gson: Is there an easier way to serialize a map

Only the TypeToken part is neccesary (when there are Generics involved).

Map<String, String> myMap = new HashMap<String, String>();
myMap.put("one", "hello");
myMap.put("two", "world");

Gson gson = new GsonBuilder().create();
String json = gson.toJson(myMap);


Type typeOfHashMap = new TypeToken<Map<String, String>>() { }.getType();
Map<String, String> newMap = gson.fromJson(json, typeOfHashMap); // This type must match TypeToken



How do I use Assert to verify that an exception has been thrown?

In case of using NUnit, try this:

Assert.That(() =>
        }, Throws.TypeOf<Your_Specific_Exception>().With.Message.EqualTo("Your_Specific_Message"));

"Char cannot be dereferenced" error

A char doesn't have any methods - it's a Java primitive. You're looking for the Character wrapper class.

The usage would be:

if(Character.isLetter(ch)) { //... }

Android: how to handle button click

Option 1 and 2 involves using inner class that will make the code kind of clutter. Option 2 is sort of messy because there will be one listener for every button. If you have small number of button, this is okay. For option 4 I think this will be harder to debug as you will have to go back and fourth the xml and java code. I personally use option 3 when I have to handle multiple button clicks.

How can I update my ADT in Eclipse?

Running as administrator then following other comments fixed the problem for me :)

Will the IE9 WebBrowser Control Support all of IE9's features, including SVG?

I came to this solution and it did not worked for me! Because I was using 64bit I had to replace the registry:


Instead of the one that everyone talks about:


Laravel 4: how to run a raw SQL?

In the Laravel 4 manual - it talks about doing raw commands like this:

DB::select(DB::raw('RENAME TABLE photos TO images'));

edit: I just found this in the Laravel 4 documentation which is probably better:

DB::statement('drop table users');

Update: In Laravel 4.1 (maybe 4.0 - I'm not sure) - you can also do this for a raw Where query:

$users = User::whereRaw('age > ? and votes = 100', array(25))->get();

Further Update If you are specifically looking to do a table rename - there is a schema command for that - see Mike's answer below for that.

jQuery: How to detect window width on the fly?

Below is what i did to hide some Id element when screen size is below 768px, and show up when is above 768px. It works great.

var screensize= $( window ).width();

                $('#column-d0f6e77c699556473e4ff2967e9c0251').removeAttr( "style" );

changething = function(screensize){
                $('#column-d0f6e77c699556473e4ff2967e9c0251').removeAttr( "style" );

$( window ).resize(function() {
 var screensize= $( window ).width();

How to clear File Input

Clear file input with jQuery


Clear file input with JavaScript

document.getElementById("fileInputId").value = null;

laravel throwing MethodNotAllowedHttpException

My problem was not that my routes were set up incorrectly, but that I was referencing the wrong Form method (which I had copied from a different form). I was doing...

{!! Form::model([ ... ]) !!}

(with no model specified). But I should have been using the regular open method...

{!! Form::open([ ... ]) !!}

Because the first parameter to model expect an actual model, it was not getting any of my options I was specifying. Hope this helps someone who knows their routes are correct, but something else is amiss.

How can I change the language (to english) in Oracle SQL Developer?

Try to set user.language and properties in sqldeveloper.conf file located in sqldeveloper\bin folder (%APPDATA%\sqldeveloper\<version>\product.conf for more recent versions) .
Sample for set french language:

IncludeConfFile ../../ide/bin/ide.conf

SetJavaHome D:\jdk1.6.0_25

AddVMOption  -Doracle.ide.util.AddinPolicyUtils.OVERRIDE_FLAG=true

AddVMOption -Dsun.java2d.ddoffscreen=false

AddVMOption -Duser.language=fr
AddVMOption  -XX:MaxPermSize=128M

AddVMOption -Doracle.jdbc.mapDateToTimestamp=false  
IncludeConfFile  sqldeveloper-nondebug.conf

To switch off language try to remove its support by editing oracle.translated.locales option in ide.boot file (located in ide\bin folder).
For example, if I want to 'break' french language support this option will be:

oracle.translated.locales = de,es,it,ja,ko,pt_BR,zh_CN,zh_TW

The original value was:

oracle.translated.locales = de,fr,es,it,ja,ko,pt_BR,zh_CN,zh_TW

The configuration above (sqldeveloper.conf file) will be wrong after remove french support and the french language does not appear as GUI localization.

Assign variable value inside if-statement

I believe that your problem is due to the fact that you are defining the variable v inside the test. As explained by @rmalchow, it will work you change it into

int v;
if((v = someMethod()) != 0) return true;

There is also another issue of variable scope. Even if what you tried were to work, what would be the point? Assuming you could define the variable scope inside the test, your variable v would not exist outside that scope. Hence, creating the variable and assigning the value would be pointless, for you would not be able to use it.

Variables exist only in the scope they were created. Since you are assigning the value to use it afterwards, consider the scope where you are creating the varible so that it may be used where needed.

Format number to always show 2 decimal places

If you're already using jQuery, you could look at using the jQuery Number Format plugin.

The plugin can return formatted numbers as a string, you can set decimal, and thousands separators, and you can choose the number of decimals to show.

$.number( 123, 2 ); // Returns '123.00'

You can also get jQuery Number Format from GitHub.

Recommended Fonts for Programming?

Don't forget the colours!

For some reason Delphi 7 in Twilight does not render Droid Sans Mono well, but in Visual Studio with an orange on black theme it is excellent. Deja Vu Sans Mono is the best all rounder. I use it almost everywhere. Consolas would be excellent apart from its ugly Q glyph.

One other thing I have found since I entered the world of work is that even though I have great eyesight I like to keep my code font around 12 or 13pt size both to reduce eye strain and to make sure I can't put too much text on screen. It's sort of an incentive to keep code blocks vertically short.

I note that this edit box does not respect my browser's default monospaced font. It's giving me Monaco (I'm on OSX). Monaco is horrible. It's glyphs have poorly angled elements and it's capitals are not well proportioned.

Oh, and it almost doesn't matter on Windows because your font will not look right anyway. /me dons flame retardent suit

How do I log a Python error with debug information?

This answer builds up from the above excellent ones.

In most applications, you won't be calling logging.exception(e) directly. Most likely you have defined a custom logger specific for your application or module like this:

# Set the name of the app or module
my_logger = logging.getLogger('NEM Sequencer')
# Set the log level

# Let's say we want to be fancy and log to a graylog2 log server
graylog_handler = graypy.GELFHandler('some_server_ip', 12201)

In this case, just use the logger to call the exception(e) like this:

except ZeroDivisionError, e:

using BETWEEN in WHERE condition

You should use

$this->db->where('$accommodation >=', minvalue);
$this->db->where('$accommodation <=', maxvalue);

I'm not sure of syntax, so I beg your pardon if it's not correct.
Anyway BETWEEN is implemented using >=min && <=max.
This is the meaning of my example.

Looking at this link I think you could write:

$this->db->where("$accommodation BETWEEN $minvalue AND $maxvalue");

How to fix "The ConnectionString property has not been initialized"

You get this error when a datasource attempts to bind to data but cannot because it cannot find the connection string. In my experience, this is not usually due to an error in the web.config (though I am not 100% sure of this).

If you are programmatically assigning a datasource (such as a SqlDataSource) or creating a query (i.e. using a SqlConnection/SqlCommand combination), make sure you assigned it a ConnectionString.

var connection = new SqlConnection(ConfigurationManager.ConnectionStrings[nameOfString].ConnectionString);

If you are hooking up a databound element to a datasource (i.e. a GridView or ComboBox to a SqlDataSource), make sure the datasource is assigned to one of your connection strings.

Post your code (for the databound element and the web.config to be safe) and we can take a look at it.

EDIT: I think the problem is that you are trying to get the Connection String from the AppSettings area, and programmatically that is not where it exists. Try replacing that with ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString (if ConnectionString is the name of your connection string.)

Input mask for numeric and decimal

You can use jquery numeric for numbers.
The current version does allow what you're looking for but someone has changed the code a little bit and it works:


<input class="numeric" type="text" />


$(".numeric").numeric({ decimal : ".",  negative : false, scale: 3 });

This is the whole source.
And I've prepared this fiddle so you can see how it works.

How to export all collections in MongoDB?

you can create zip file by using following command .It will create zip file of database {dbname} provided.You can later import the following zip file in you mongo DB.

Window filepath=C:\Users\Username\mongo 

mongodump --archive={filepath}\+{filename}.gz --gzip --db {dbname}

How is the 'use strict' statement interpreted in Node.js?

"use strict";

Basically it enables the strict mode.

Strict Mode is a feature that allows you to place a program, or a function, in a "strict" operating context. In strict operating context, the method form binds this to the objects as before. The function form binds this to undefined, not the global set objects.

As per your comments you are telling some differences will be there. But it's your assumption. The Node.js code is nothing but your JavaScript code. All Node.js code are interpreted by the V8 JavaScript engine. The V8 JavaScript Engine is an open source JavaScript engine developed by Google for Chrome web browser.

So, there will be no major difference how "use strict"; is interpreted by the Chrome browser and Node.js.

Please read what is strict mode in JavaScript.

For more information:

  1. Strict mode
  2. ECMAScript 5 Strict mode support in browsers
  3. Strict mode is coming to town
  4. Compatibility table for strict mode
  5. Stack Overflow questions: what does 'use strict' do in JavaScript & what is the reasoning behind it

ECMAScript 6:

ECMAScript 6 Code & strict mode. Following is brief from the specification:

10.2.1 Strict Mode Code

An ECMAScript Script syntactic unit may be processed using either unrestricted or strict mode syntax and semantics. Code is interpreted as strict mode code in the following situations:

  • Global code is strict mode code if it begins with a Directive Prologue that contains a Use Strict Directive (see 14.1.1).
  • Module code is always strict mode code.
  • All parts of a ClassDeclaration or a ClassExpression are strict mode code.
  • Eval code is strict mode code if it begins with a Directive Prologue that contains a Use Strict Directive or if the call to eval is a direct eval (see that is contained in strict mode code.
  • Function code is strict mode code if the associated FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, MethodDefinition, or ArrowFunction is contained in strict mode code or if the code that produces the value of the function’s [[ECMAScriptCode]] internal slot begins with a Directive Prologue that contains a Use Strict Directive.
  • Function code that is supplied as the arguments to the built-in Function and Generator constructors is strict mode code if the last argument is a String that when processed is a FunctionBody that begins with a Directive Prologue that contains a Use Strict Directive.

Additionally if you are lost on what features are supported by your current version of Node.js, this can help you (leverages from the same data as kangax).

Create iOS Home Screen Shortcuts on Chrome for iOS

Can't change the default browser, but try this (found online a while ago). Add a bookmark in Safari called "Open in Chrome" with the following.


Will open the current page in Chrome. Not as convenient, but maybe someone will find it useful.


Works for me.

Encrypt and decrypt a password in Java

EDIT : this answer is old. Usage of MD5 is now discouraged as it can easily be broken.

MD5 must be good enough for you I imagine? You can achieve it with MessageDigest.


There are also other algorithms listed here.

And here's an third party version of it, if you really want: Fast MD5

Border color on default input style

border-color: transparent; border: 1px solid red;

Disable time in bootstrap date time picker

    $(function () {
            viewMode: 'years',
            format: 'DD/MM/YYYY' /*Add this line to remove time format*/