Programs & Examples On #Development process

A development process is a set of practices, roles and artifacts performed/created during development. **Important note:** General development methodology questions should be posted on Software Engineering SE or Project Management SE instead.

How to close a JavaFX application on window close?

Did you try this..setOnCloseRequest

setOnCloseRequest(EventHandler<WindowEvent> value)   

There is one example

string to string array conversion in java

String strName = "name";
String[] strArray = new String[] {strName};
System.out.println(strArray[0]); //prints "name"

The second line allocates a String array with the length of 1. Note that you don't need to specify a length yourself, such as:

String[] strArray = new String[1];

instead, the length is determined by the number of elements in the initalizer. Using

String[] strArray = new String[] {strName, "name1", "name2"};

creates an array with a length of 3.

How do I detect if Python is running as a 64-bit application?

While it may work on some platforms, be aware that platform.architecture is not always a reliable way to determine whether python is running in 32-bit or 64-bit. In particular, on some OS X multi-architecture builds, the same executable file may be capable of running in either mode, as the example below demonstrates. The quickest safe multi-platform approach is to test sys.maxsize on Python 2.6, 2.7, Python 3.x.

$ arch -i386 /usr/local/bin/python2.7
Python 2.7.9 (v2.7.9:648dcafa7e5f, Dec 10 2014, 10:10:46)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import platform, sys
>>> platform.architecture(), sys.maxsize
(('64bit', ''), 2147483647)
>>> ^D
$ arch -x86_64 /usr/local/bin/python2.7
Python 2.7.9 (v2.7.9:648dcafa7e5f, Dec 10 2014, 10:10:46)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import platform, sys
>>> platform.architecture(), sys.maxsize
(('64bit', ''), 9223372036854775807)

How can I quickly and easily convert spreadsheet data to JSON?

Assuming you really mean easiest and are not necessarily looking for a way to do this programmatically, you can do this:

  1. Add, if not already there, a row of "column Musicians" to the spreadsheet. That is, if you have data in columns such as:

    Rory Gallagher      Guitar
    Gerry McAvoy        Bass
    Rod de'Ath          Drums
    Lou Martin          Keyboards
    Donkey Kong Sioux   Self-Appointed Semi-official Stomper

    Note: you might want to add "Musician" and "Instrument" in row 0 (you might have to insert a row there)

  2. Save the file as a CSV file.

  3. Copy the contents of the CSV file to the clipboard

  4. Go to

  5. Verify that the "First row is column names" checkbox is checked

  6. Paste the CSV data into the content area

  7. Mash the "Convert CSV to JSON" button

    With the data shown above, you will now have:

        "MUSICIAN":"Rory Gallagher",
        "MUSICIAN":"Gerry McAvoy",
        "MUSICIAN":"Rod D'Ath",
        "MUSICIAN":"Lou Martin",
        "MUSICIAN":"Donkey Kong Sioux",
        "INSTRUMENT":"Self-Appointed Semi-Official Stomper"

    With this simple/minimalistic data, it's probably not required, but with large sets of data, it can save you time and headache in the proverbial long run by checking this data for aberrations and abnormalcy.

  8. Go here:

  9. Paste the JSON into the content area

  10. Pres the "Validate" button.

If the JSON is good, you will see a "Valid JSON" remark in the Results section below; if not, it will tell you where the problem[s] lie so that you can fix it/them.

How to delete file from public folder in laravel 5.1

this method worked for me
First, put the line below at the beginning of your controller:

use File;

below namespace in your php file Second:

 $destinationPath = 'your_path';

$destinationPath --> the folder inside folder public.

WebSocket with SSL

1 additional caveat (besides the answer by kanaka/peter): if you use WSS, and the server certificate is not acceptable to the browser, you may not get any browser rendered dialog (like it happens for Web pages). This is because WebSockets is treated as a so-called "subresource", and certificate accept / security exception / whatever dialogs are not rendered for subresources.

How to get nth jQuery element

You can use the :eq selector, for example:

$("td:eq(2)").css("color", "red"); // gets the third td element

Or the eq(int) function:

$("td").eq(2).css("color", "red");

Also, remember that the indexes are zero-based.

Define make variable at rule execution time

In your example, the TMP variable is set (and the temporary directory created) whenever the rules for out.tar are evaluated. In order to create the directory only when out.tar is actually fired, you need to move the directory creation down into the steps:

out.tar : 
    $(eval TMP := $(shell mktemp -d))
    @echo hi $(TMP)/hi.txt
    tar -C $(TMP) cf $@ .
    rm -rf $(TMP)

The eval function evaluates a string as if it had been typed into the makefile manually. In this case, it sets the TMP variable to the result of the shell function call.

edit (in response to comments):

To create a unique variable, you could do the following:

out.tar : 
    $(eval $@_TMP := $(shell mktemp -d))
    @echo hi $($@_TMP)/hi.txt
    tar -C $($@_TMP) cf $@ .
    rm -rf $($@_TMP)

This would prepend the name of the target (out.tar, in this case) to the variable, producing a variable with the name out.tar_TMP. Hopefully, that is enough to prevent conflicts.

Android Endless List

You can detect end of the list with help of onScrollListener, working code is presented below:

public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
    if (view.getAdapter() != null && ((firstVisibleItem + visibleItemCount) >= totalItemCount) && totalItemCount != mPrevTotalItemCount) {
        Log.v(TAG, "onListEnd, extending list");
        mPrevTotalItemCount = totalItemCount;

Another way to do that (inside adapter) is as following:

    public View getView(int pos, View v, ViewGroup p) {
                addMoreData(); //should be asynctask or thread
            return view;

Be aware that this method will be called many times, so you need to add another condition to block multiple calls of addMoreData().

When you add all elements to the list, please call notifyDataSetChanged() inside yours adapter to update the View (it should be run on UI thread - runOnUiThread)

PHP function use variable from outside

Do not forget that you also can pass these use variables by reference.

The use cases are when you need to change the use'd variable from inside of your callback (e.g. produce the new array of different objects from some source array of objects).

$sourcearray = [ (object) ['a' => 1], (object) ['a' => 2]];
$newarray = [];
array_walk($sourcearray, function ($item) use (&$newarray) {
    $newarray[] = (object) ['times2' => $item->a * 2];

Now $newarray will comprise (pseudocode here for brevity) [{times2:2},{times2:4}].

On the contrary, using $newarray with no & modifier would make outer $newarray variable be read-only accessible from within the closure scope. But $newarray within closure scope would be a completelly different newly created variable living only within the closure scope.

Despite both variables' names are the same these would be two different variables. The outer $newarray variable would comprise [] in this case after the code has finishes.

Why are primes important in cryptography?

I would suggest the book A Mathematical Journey In Code. The book has a nice down to earth feel, which is surprising, since it is about cryptography. The book summarizes Sarah Flannery’s journey from learning puzzles as a child to creating the Cayley-Purser (CP) algorithm at the age of 16. It gives an amazingly detailed explanation of one way functions, number theory, and prime numbers and how they relate to cryptography.

What makes this book even more specific to your question is Sarah tried to implement a new public key algorithm using matrix's. It was much faster then using prime numbers but a loop hole was found that could exploit it. It turns out her algorithm was better used as a private encryption mechanism. The book is a great testament to using prime numbers for encryption as it has stood the test of time and the challenges of very smart individuals.

How to change bower's default components folder?

In addition to editing .bowerrc to setup your default install path, you can also setup custom install paths for different file types.

There is a node package called bower-installer that provides a single command for managing alternate install paths.

run npm install -g bower-installer

Set up your bower.json

  "name" : "test",
  "version": "0.1",
  "dependencies" : {
    "jquery-ui" : "latest"
  "install" : {
    "path" : {
      "css": "src/css",
      "js": "src/js"
    "sources" : {
      "jquery-ui" : [

Run the following command: bower-installer

This will install components/jquery-ui/themes/start/jquery-ui.css to ./src/css, etc

Setting background-image using jQuery CSS property

You probably want this (to make it like a normal CSS background-image declaration):

$('myObject').css('background-image', 'url(' + imageUrl + ')');

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

Spring application context external properties?

<context:property-placeholder location="classpath*:spring/*.properties" />

If you place it somewhere in the classpath in a directory named spring (change names/dirs accordingly), you can access with above

<property name="locations" value ="config/" />

this will be pointing to web-inf/classes/config/


Welcome to the wonderful world of portability... or rather the lack of it. Before we start analyzing these two options in detail and take a deeper look how different operating systems handle them, it should be noted that the BSD socket implementation is the mother of all socket implementations. Basically all other systems copied the BSD socket implementation at some point in time (or at least its interfaces) and then started evolving it on their own. Of course the BSD socket implementation was evolved as well at the same time and thus systems that copied it later got features that were lacking in systems that copied it earlier. Understanding the BSD socket implementation is the key to understanding all other socket implementations, so you should read about it even if you don't care to ever write code for a BSD system.

There are a couple of basics you should know before we look at these two options. A TCP/UDP connection is identified by a tuple of five values:

{<protocol>, <src addr>, <src port>, <dest addr>, <dest port>}

Any unique combination of these values identifies a connection. As a result, no two connections can have the same five values, otherwise the system would not be able to distinguish these connections any longer.

The protocol of a socket is set when a socket is created with the socket() function. The source address and port are set with the bind() function. The destination address and port are set with the connect() function. Since UDP is a connectionless protocol, UDP sockets can be used without connecting them. Yet it is allowed to connect them and in some cases very advantageous for your code and general application design. In connectionless mode, UDP sockets that were not explicitly bound when data is sent over them for the first time are usually automatically bound by the system, as an unbound UDP socket cannot receive any (reply) data. Same is true for an unbound TCP socket, it is automatically bound before it will be connected.

If you explicitly bind a socket, it is possible to bind it to port 0, which means "any port". Since a socket cannot really be bound to all existing ports, the system will have to choose a specific port itself in that case (usually from a predefined, OS specific range of source ports). A similar wildcard exists for the source address, which can be "any address" ( in case of IPv4 and :: in case of IPv6). Unlike in case of ports, a socket can really be bound to "any address" which means "all source IP addresses of all local interfaces". If the socket is connected later on, the system has to choose a specific source IP address, since a socket cannot be connected and at the same time be bound to any local IP address. Depending on the destination address and the content of the routing table, the system will pick an appropriate source address and replace the "any" binding with a binding to the chosen source IP address.

By default, no two sockets can be bound to the same combination of source address and source port. As long as the source port is different, the source address is actually irrelevant. Binding socketA to ipA:portA and socketB to ipB:portB is always possible if ipA != ipB holds true, even when portA == portB. E.g. socketA belongs to a FTP server program and is bound to and socketB belongs to another FTP server program and is bound to, both bindings will succeed. Keep in mind, though, that a socket may be locally bound to "any address". If a socket is bound to, it is bound to all existing local addresses at the same time and in that case no other socket can be bound to port 21, regardless which specific IP address it tries to bind to, as conflicts with all existing local IP addresses.

Anything said so far is pretty much equal for all major operating system. Things start to get OS specific when address reuse comes into play. We start with BSD, since as I said above, it is the mother of all socket implementations.



If SO_REUSEADDR is enabled on a socket prior to binding it, the socket can be successfully bound unless there is a conflict with another socket bound to exactly the same combination of source address and port. Now you may wonder how is that any different than before? The keyword is "exactly". SO_REUSEADDR mainly changes the way how wildcard addresses ("any IP address") are treated when searching for conflicts.

Without SO_REUSEADDR, binding socketA to and then binding socketB to will fail (with error EADDRINUSE), since means "any local IP address", thus all local IP addresses are considered in use by this socket and this includes, too. With SO_REUSEADDR it will succeed, since and are not exactly the same address, one is a wildcard for all local addresses and the other one is a very specific local address. Note that the statement above is true regardless in which order socketA and socketB are bound; without SO_REUSEADDR it will always fail, with SO_REUSEADDR it will always succeed.

To give you a better overview, let's make a table here and list all possible combinations:

SO_REUSEADDR       socketA        socketB       Result
  ON/OFF    OK
  ON/OFF    OK
   OFF       Error (EADDRINUSE)
   OFF    Error (EADDRINUSE)
   ON        OK
   ON    OK

The table above assumes that socketA has already been successfully bound to the address given for socketA, then socketB is created, either gets SO_REUSEADDR set or not, and finally is bound to the address given for socketB. Result is the result of the bind operation for socketB. If the first column says ON/OFF, the value of SO_REUSEADDR is irrelevant to the result.

Okay, SO_REUSEADDR has an effect on wildcard addresses, good to know. Yet that isn't it's only effect it has. There is another well known effect which is also the reason why most people use SO_REUSEADDR in server programs in the first place. For the other important use of this option we have to take a deeper look on how the TCP protocol works.

A socket has a send buffer and if a call to the send() function succeeds, it does not mean that the requested data has actually really been sent out, it only means the data has been added to the send buffer. For UDP sockets, the data is usually sent pretty soon, if not immediately, but for TCP sockets, there can be a relatively long delay between adding data to the send buffer and having the TCP implementation really send that data. As a result, when you close a TCP socket, there may still be pending data in the send buffer, which has not been sent yet but your code considers it as sent, since the send() call succeeded. If the TCP implementation was closing the socket immediately on your request, all of this data would be lost and your code wouldn't even know about that. TCP is said to be a reliable protocol and losing data just like that is not very reliable. That's why a socket that still has data to send will go into a state called TIME_WAIT when you close it. In that state it will wait until all pending data has been successfully sent or until a timeout is hit, in which case the socket is closed forcefully.

At most, the amount of time the kernel will wait before it closes the socket, regardless if it still has data in flight or not, is called the Linger Time. The Linger Time is globally configurable on most systems and by default rather long (two minutes is a common value you will find on many systems). It is also configurable per socket using the socket option SO_LINGER which can be used to make the timeout shorter or longer, and even to disable it completely. Disabling it completely is a very bad idea, though, since closing a TCP socket gracefully is a slightly complex process and involves sending forth and back a couple of packets (as well as resending those packets in case they got lost) and this whole close process is also limited by the Linger Time. If you disable lingering, your socket may not only lose data in flight, it is also always closed forcefully instead of gracefully, which is usually not recommended. The details about how a TCP connection is closed gracefully are beyond the scope of this answer, if you want to learn more about, I recommend you have a look at this page. And even if you disabled lingering with SO_LINGER, if your process dies without explicitly closing the socket, BSD (and possibly other systems) will linger nonetheless, ignoring what you have configured. This will happen for example if your code just calls exit() (pretty common for tiny, simple server programs) or the process is killed by a signal (which includes the possibility that it simply crashes because of an illegal memory access). So there is nothing you can do to make sure a socket will never linger under all circumstances.

The question is, how does the system treat a socket in state TIME_WAIT? If SO_REUSEADDR is not set, a socket in state TIME_WAIT is considered to still be bound to the source address and port and any attempt to bind a new socket to the same address and port will fail until the socket has really been closed, which may take as long as the configured Linger Time. So don't expect that you can rebind the source address of a socket immediately after closing it. In most cases this will fail. However, if SO_REUSEADDR is set for the socket you are trying to bind, another socket bound to the same address and port in state TIME_WAIT is simply ignored, after all its already "half dead", and your socket can bind to exactly the same address without any problem. In that case it plays no role that the other socket may have exactly the same address and port. Note that binding a socket to exactly the same address and port as a dying socket in TIME_WAIT state can have unexpected, and usually undesired, side effects in case the other socket is still "at work", but that is beyond the scope of this answer and fortunately those side effects are rather rare in practice.

There is one final thing you should know about SO_REUSEADDR. Everything written above will work as long as the socket you want to bind to has address reuse enabled. It is not necessary that the other socket, the one which is already bound or is in a TIME_WAIT state, also had this flag set when it was bound. The code that decides if the bind will succeed or fail only inspects the SO_REUSEADDR flag of the socket fed into the bind() call, for all other sockets inspected, this flag is not even looked at.


SO_REUSEPORT is what most people would expect SO_REUSEADDR to be. Basically, SO_REUSEPORT allows you to bind an arbitrary number of sockets to exactly the same source address and port as long as all prior bound sockets also had SO_REUSEPORT set before they were bound. If the first socket that is bound to an address and port does not have SO_REUSEPORT set, no other socket can be bound to exactly the same address and port, regardless if this other socket has SO_REUSEPORT set or not, until the first socket releases its binding again. Unlike in case of SO_REUESADDR the code handling SO_REUSEPORT will not only verify that the currently bound socket has SO_REUSEPORT set but it will also verify that the socket with a conflicting address and port had SO_REUSEPORT set when it was bound.

SO_REUSEPORT does not imply SO_REUSEADDR. This means if a socket did not have SO_REUSEPORT set when it was bound and another socket has SO_REUSEPORT set when it is bound to exactly the same address and port, the bind fails, which is expected, but it also fails if the other socket is already dying and is in TIME_WAIT state. To be able to bind a socket to the same addresses and port as another socket in TIME_WAIT state requires either SO_REUSEADDR to be set on that socket or SO_REUSEPORT must have been set on both sockets prior to binding them. Of course it is allowed to set both, SO_REUSEPORT and SO_REUSEADDR, on a socket.

There is not much more to say about SO_REUSEPORT other than that it was added later than SO_REUSEADDR, that's why you will not find it in many socket implementations of other systems, which "forked" the BSD code before this option was added, and that there was no way to bind two sockets to exactly the same socket address in BSD prior to this option.

Connect() Returning EADDRINUSE?

Most people know that bind() may fail with the error EADDRINUSE, however, when you start playing around with address reuse, you may run into the strange situation that connect() fails with that error as well. How can this be? How can a remote address, after all that's what connect adds to a socket, be already in use? Connecting multiple sockets to exactly the same remote address has never been a problem before, so what's going wrong here?

As I said on the very top of my reply, a connection is defined by a tuple of five values, remember? And I also said, that these five values must be unique otherwise the system cannot distinguish two connections any longer, right? Well, with address reuse, you can bind two sockets of the same protocol to the same source address and port. That means three of those five values are already the same for these two sockets. If you now try to connect both of these sockets also to the same destination address and port, you would create two connected sockets, whose tuples are absolutely identical. This cannot work, at least not for TCP connections (UDP connections are no real connections anyway). If data arrived for either one of the two connections, the system could not tell which connection the data belongs to. At least the destination address or destination port must be different for either connection, so that the system has no problem to identify to which connection incoming data belongs to.

So if you bind two sockets of the same protocol to the same source address and port and try to connect them both to the same destination address and port, connect() will actually fail with the error EADDRINUSE for the second socket you try to connect, which means that a socket with an identical tuple of five values is already connected.

Multicast Addresses

Most people ignore the fact that multicast addresses exist, but they do exist. While unicast addresses are used for one-to-one communication, multicast addresses are used for one-to-many communication. Most people got aware of multicast addresses when they learned about IPv6 but multicast addresses also existed in IPv4, even though this feature was never widely used on the public Internet.

The meaning of SO_REUSEADDR changes for multicast addresses as it allows multiple sockets to be bound to exactly the same combination of source multicast address and port. In other words, for multicast addresses SO_REUSEADDR behaves exactly as SO_REUSEPORT for unicast addresses. Actually, the code treats SO_REUSEADDR and SO_REUSEPORT identically for multicast addresses, that means you could say that SO_REUSEADDR implies SO_REUSEPORT for all multicast addresses and the other way round.


All these are rather late forks of the original BSD code, that's why they all three offer the same options as BSD and they also behave the same way as in BSD.

macOS (MacOS X)

At its core, macOS is simply a BSD-style UNIX named "Darwin", based on a rather late fork of the BSD code (BSD 4.3), which was then later on even re-synchronized with the (at that time current) FreeBSD 5 code base for the Mac OS 10.3 release, so that Apple could gain full POSIX compliance (macOS is POSIX certified). Despite having a microkernel at its core ("Mach"), the rest of the kernel ("XNU") is basically just a BSD kernel, and that's why macOS offers the same options as BSD and they also behave the same way as in BSD.

iOS / watchOS / tvOS

iOS is just a macOS fork with a slightly modified and trimmed kernel, somewhat stripped down user space toolset and a slightly different default framework set. watchOS and tvOS are iOS forks, that are stripped down even further (especially watchOS). To my best knowledge they all behave exactly as macOS does.


Linux < 3.9

Prior to Linux 3.9, only the option SO_REUSEADDR existed. This option behaves generally the same as in BSD with two important exceptions:

  1. As long as a listening (server) TCP socket is bound to a specific port, the SO_REUSEADDR option is entirely ignored for all sockets targeting that port. Binding a second socket to the same port is only possible if it was also possible in BSD without having SO_REUSEADDR set. E.g. you cannot bind to a wildcard address and then to a more specific one or the other way round, both is possible in BSD if you set SO_REUSEADDR. What you can do is you can bind to the same port and two different non-wildcard addresses, as that's always allowed. In this aspect Linux is more restrictive than BSD.

  2. The second exception is that for client sockets, this option behaves exactly like SO_REUSEPORT in BSD, as long as both had this flag set before they were bound. The reason for allowing that was simply that it is important to be able to bind multiple sockets to exactly to the same UDP socket address for various protocols and as there used to be no SO_REUSEPORT prior to 3.9, the behavior of SO_REUSEADDR was altered accordingly to fill that gap. In that aspect Linux is less restrictive than BSD.

Linux >= 3.9

Linux 3.9 added the option SO_REUSEPORT to Linux as well. This option behaves exactly like the option in BSD and allows binding to exactly the same address and port number as long as all sockets have this option set prior to binding them.

Yet, there are still two differences to SO_REUSEPORT on other systems:

  1. To prevent "port hijacking", there is one special limitation: All sockets that want to share the same address and port combination must belong to processes that share the same effective user ID! So one user cannot "steal" ports of another user. This is some special magic to somewhat compensate for the missing SO_EXCLBIND/SO_EXCLUSIVEADDRUSE flags.

  2. Additionally the kernel performs some "special magic" for SO_REUSEPORT sockets that isn't found in other operating systems: For UDP sockets, it tries to distribute datagrams evenly, for TCP listening sockets, it tries to distribute incoming connect requests (those accepted by calling accept()) evenly across all the sockets that share the same address and port combination. Thus an application can easily open the same port in multiple child processes and then use SO_REUSEPORT to get a very inexpensive load balancing.


Even though the whole Android system is somewhat different from most Linux distributions, at its core works a slightly modified Linux kernel, thus everything that applies to Linux should apply to Android as well.


Windows only knows the SO_REUSEADDR option, there is no SO_REUSEPORT. Setting SO_REUSEADDR on a socket in Windows behaves like setting SO_REUSEPORT and SO_REUSEADDR on a socket in BSD, with one exception:

Prior to Windows 2003, a socket with SO_REUSEADDR could always been bound to exactly the same source address and port as an already bound socket, even if the other socket did not have this option set when it was bound. This behavior allowed an application "to steal" the connected port of another application. Needless to say that this has major security implications!

Microsoft realized that and added another important socket option: SO_EXCLUSIVEADDRUSE. Setting SO_EXCLUSIVEADDRUSE on a socket makes sure that if the binding succeeds, the combination of source address and port is owned exclusively by this socket and no other socket can bind to them, not even if it has SO_REUSEADDR set.

This default behavior was changed first in Windows 2003, Microsoft calls that "Enhanced Socket Security" (funny name for a behavior that is default on all other major operating systems). For more details just visit this page. There are three tables: The first one shows the classic behavior (still in use when using compatibility modes!), the second one shows the behavior of Windows 2003 and up when the bind() calls are made by the same user, and the third one when the bind() calls are made by different users.


Solaris is the successor of SunOS. SunOS was originally based on a fork of BSD, SunOS 5 and later was based on a fork of SVR4, however SVR4 is a merge of BSD, System V, and Xenix, so up to some degree Solaris is also a BSD fork, and a rather early one. As a result Solaris only knows SO_REUSEADDR, there is no SO_REUSEPORT. The SO_REUSEADDR behaves pretty much the same as it does in BSD. As far as I know there is no way to get the same behavior as SO_REUSEPORT in Solaris, that means it is not possible to bind two sockets to exactly the same address and port.

Similar to Windows, Solaris has an option to give a socket an exclusive binding. This option is named SO_EXCLBIND. If this option is set on a socket prior to binding it, setting SO_REUSEADDR on another socket has no effect if the two sockets are tested for an address conflict. E.g. if socketA is bound to a wildcard address and socketB has SO_REUSEADDR enabled and is bound to a non-wildcard address and the same port as socketA, this bind will normally succeed, unless socketA had SO_EXCLBIND enabled, in which case it will fail regardless the SO_REUSEADDR flag of socketB.

Other Systems

In case your system is not listed above, I wrote a little test program that you can use to find out how your system handles these two options. Also if you think my results are wrong, please first run that program before posting any comments and possibly making false claims.

All that the code requires to build is a bit POSIX API (for the network parts) and a C99 compiler (actually most non-C99 compiler will work as well as long as they offer inttypes.h and stdbool.h; e.g. gcc supported both long before offering full C99 support).

All that the program needs to run is that at least one interface in your system (other than the local interface) has an IP address assigned and that a default route is set which uses that interface. The program will gather that IP address and use it as the second "specific address".

It tests all possible combinations you can think of:

  • TCP and UDP protocol
  • Normal sockets, listen (server) sockets, multicast sockets
  • SO_REUSEADDR set on socket1, socket2, or both sockets
  • SO_REUSEPORT set on socket1, socket2, or both sockets
  • All address combinations you can make out of (wildcard), (specific address), and the second specific address found at your primary interface (for multicast it's just in all tests)

and prints the results in a nice table. It will also work on systems that don't know SO_REUSEPORT, in which case this option is simply not tested.

What the program cannot easily test is how SO_REUSEADDR acts on sockets in TIME_WAIT state as it's very tricky to force and keep a socket in that state. Fortunately most operating systems seems to simply behave like BSD here and most of the time programmers can simply ignore the existence of that state.

Here's the code (I cannot include it here, answers have a size limit and the code would push this reply over the limit).

MySQL Cannot Add Foreign Key Constraint

To set a FOREIGN KEY in Table B you must set a KEY in the table A.

In table A: INDEX id (id)

And then in the table B,


Cannot import XSSF in Apache POI

1) imported all the JARS from POI folder 2) Imported all the JARS from ooxml folder which a subdirectory of POI folder 3) Imported all the JARS from lib folder which is a subdirectory of POI folder

String fileName = "C:/File raw.xlsx";
File file = new File(fileName);
FileInputStream fileInputStream;
Workbook workbook = null;
Sheet sheet;
Iterator<Row> rowIterator;
try {
        fileInputStream = new FileInputStream(file);
        String fileExtension = fileName.substring(fileName.indexOf("."));
        workbook  = new HSSFWorkbook(new POIFSFileSystem(fileInputStream));
        else if(fileExtension.equals(".xlsx")){
        workbook  = new XSSFWorkbook(fileInputStream);
        else {
        System.out.println("Wrong File Type");
        FormulaEvaluator evaluator workbook.getCreationHelper().createFormulaEvaluator();
        sheet = workbook.getSheetAt(0);
        rowIterator = sheet.iterator();
        Row row =;
        Iterator<Cell> cellIterator = row.cellIterator();
        while (cellIterator.hasNext()){
        Cell cell =;
        //Check the cell type after evaluating formulae
       //If it is formula cell, it will be evaluated otherwise no change will happen
        switch (evaluator.evaluateInCell(cell).getCellType()){
        case Cell.CELL_TYPE_NUMERIC:
        System.out.print(cell.getNumericCellValue() + " ");
        case Cell.CELL_TYPE_STRING:
        System.out.print(cell.getStringCellValue() + " ");
        case Cell.CELL_TYPE_FORMULA:
        Not again
        case Cell.CELL_TYPE_BLANK:
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
} catch (IOException e){

Design Android EditText to show error message as described by google

TextInputLayout til = (TextInputLayout)editText.getParent();
til.setError("some error..");

How to add calendar events in Android?

Try this in your code:

Calendar cal = Calendar.getInstance();              
Intent intent = new Intent(Intent.ACTION_EDIT);
intent.putExtra("beginTime", cal.getTimeInMillis());
intent.putExtra("allDay", true);
intent.putExtra("rrule", "FREQ=YEARLY");
intent.putExtra("endTime", cal.getTimeInMillis()+60*60*1000);
intent.putExtra("title", "A Test Event from android app");

How to start rails server?

I also faced the same issue, but my fault was that I was running "rails s" outside of my application directory. After opening the cmd, just go inside your application and run the commands from their, it worked for me.

Bootstrap modal - close modal when "call to action" button is clicked

You need to bind the modal hide call to the onclick event.

Assuming you are using jQuery you can do that with:

$('#closemodal').click(function() {

Also make sure the click event is bound after the document has finished loading:

$(function() {
   // Place the above code inside this block
enter code here

How can I put a database under git (version control)?

I would recommend neXtep for version controlling the database it has got a good set of documentation and forums that explains how to install and the errors encountered. I have tested it for postgreSQL 9.1 and 9.3, i was able to get it working for 9.1 but for 9.3 it doesn't seems to work.

How do I check which version of NumPy I'm using?

From the command line, you can simply issue:

python -c "import numpy; print(numpy.version.version)"


python -c "import numpy; print(numpy.__version__)"

Runtime vs. Compile time

Basically if your compiler can work out what you mean or what a value is "at compile time" it can hardcode this into the runtime code. Obviously if your runtime code has to do a calculation every time it will run slower, so if you can determine something at compile time it is much better.


Constant folding:

If I write:

int i = 2;

The compiler can perform this calulation at compile time because it knows what 2 is, and what MY_CONSTANT is. As such it saves itself from performing a calculation every single execution.

HTTP Status 500 - Servlet.init() for servlet Dispatcher threw exception

<project xmlns="" xmlns:xsi=""

            <name>PrimeFaces Maven Repository</name>








Is it possible for UIStackView to scroll?

In case anyone is looking for a solution without code, I created an example to do this completely in the storyboard, using Auto Layout.

You can get it from github.

Basically, to recreate the example (for vertical scrolling):

  1. Create a UIScrollView, and set its constraints.
  2. Add a UIStackView to the UIScrollView
  3. Set the constraints: Leading, Trailing, Top & Bottom should be equal to the ones from UIScrollView
  4. Set up an equal Width constraint between the UIStackView and UIScrollView.
  5. Set Axis = Vertical, Alignment = Fill, Distribution = Equal Spacing, and Spacing = 0 on the UIStackView
  6. Add a number of UIViews to the UIStackView
  7. Run

Exchange Width for Height in step 4, and set Axis = Horizontal in step 5, to get a horizontal UIStackView.

How to kill MySQL connections

As above mentioned, there is no special command to do it. However, if all those connection are inactive, using 'flush tables;' is able to release all those connection which are not active.

Shortest way to check for null and assign another value if not

Use the C# coalesce operator: ??

// if Value is not null, newValue = Value else if Value is null newValue is YournullValue
var newValue = Value ?? YourNullReplacement;

Select All as default value for Multivalue parameter

The accepted answer is correct, but not complete. In order for Select All to be the default option, the Available Values dataset must contain at least 2 columns: value and label. They can return the same data, but their names have to be different. The Default Values dataset will then use value column and then Select All will be the default value. If the dataset returns only 1 column, only the last record's value will be selected in the drop down of the parameter.

Replace Multiple String Elements in C#

I'm doing something similar, but in my case I'm doing serialization/De-serialization so I need to be able to go both directions. I find using a string[][] works nearly identically to the dictionary, including initialization, but you can go the other direction too, returning the substitutes to their original values, something that the dictionary really isn't set up to do.

Edit: You can use Dictionary<Key,List<Values>> in order to obtain same result as string[][]

Conditionally displaying JSF components

Yes, use the rendered attribute.

<h:form rendered="#{some boolean condition}">

You usually tie it to the model rather than letting the model grab the component and manipulate it.


<h:form rendered="#{bean.booleanValue}" />
<h:form rendered="#{bean.intValue gt 10}" />
<h:form rendered="#{bean.objectValue eq null}" />
<h:form rendered="#{bean.stringValue ne 'someValue'}" />
<h:form rendered="#{not empty bean.collectionValue}" />
<h:form rendered="#{not bean.booleanValue and bean.intValue ne 0}" />
<h:form rendered="#{bean.enumValue eq 'ONE' or bean.enumValue eq 'TWO'}" />

Note the importance of keyword based EL operators such as gt, ge, le and lt instead of >, >=, <= and < as angle brackets < and > are reserved characters in XML. See also this related Q&A: Error parsing XHTML: The content of elements must consist of well-formed character data or markup.

As to your specific use case, let's assume that the link is passing a parameter like below:

<a href="page.xhtml?form=1">link</a>

You can then show the form as below:

<h:form rendered="#{param.form eq '1'}">

(the #{param} is an implicit EL object referring to a Map representing the request parameters)

See also:

Where does application data file actually stored on android device?

Use Context.getDatabasePath(databasename). The context can be obtained from your application.

If you get previous data back it can be either a) the data was stored in an unconventional location and therefore not deleted with uninstall or b) Titanium backed up the data with the app (it can do that).

"Cloning" row or column vectors

To answer the actual question, now that nearly a dozen approaches to working around a solution have been posted: x.transpose reverses the shape of x. One of the interesting side-effects is that if x.ndim == 1, the transpose does nothing.

This is especially confusing for people coming from MATLAB, where all arrays implicitly have at least two dimensions. The correct way to transpose a 1D numpy array is not x.transpose() or x.T, but rather

x[:, None]


x.reshape(-1, 1)

From here, you can multiply by a matrix of ones, or use any of the other suggested approaches, as long as you respect the (subtle) differences between MATLAB and numpy.

Copy values from one column to another in the same table

you can do it with Procedure also so i have a procedure for this

               DECLARE x  INT;
            DECLARE str varchar(45);
              SET x = 1;
            set str = '';
              WHILE x < 5 DO
                set  str = (select source_col from emp where id=x);
            update emp set target_col =str where id=x;      
            SET  x = x + 1;
                END WHILE;


Git reset --hard and push to remote repository

The whole git resetting business looked far to complicating for me.

So I did something along the lines to get my src folder in the state i had a few commits ago

# reset the local state
git reset <somecommit> --hard 
# copy the relevant part e.g. src (exclude is only needed if you specify .)
tar cvfz /tmp/current.tgz --exclude .git  src
# get the current state of git
git pull
# remove what you don't like anymore
rm -rf src
# restore from the tar file
tar xvfz /tmp/current.tgz
# commit everything back to git
git commit -a
# now you can properly push
git push

This way the state of affairs in the src is kept in a tar file and git is forced to accept this state without too much fiddling basically the src directory is replaced with the state it had several commits ago.

Installing Apple's Network Link Conditioner Tool

  1. Remove "Network Link Conditioner", open "System Preferences", press CTRL and click the "Network Link Conditioner" icon. Select "Remove".
  2. Restart your computer
  3. Download the dmg "Hardware IO tools" for your XCode version from, you need to be logged in to do this.
  4. Open it and install "Network Link Conditioner"
  5. Restart your computer one last time.

need to test if sql query was successful

if you're not using the -> format, you can do this:

$a = "SQL command...";
if ($b = mysqli_query($con,$a)) {
  // results was successful
} else {
  // result was not successful

Convert dd-mm-yyyy string to date

var from = $("#datepicker").val(); 
var f = $.datepicker.parseDate("d-m-Y", from);

orderBy multiple fields in Angular

Created Pipe for sorting. Accepts both string and array of strings, sorting by multiple values. Works for Angular (not AngularJS). Supports both sort for string and numbers.

@Pipe({name: 'orderBy'})
export class OrderBy implements PipeTransform {
    transform(array: any[], filter: any): any[] {
        if(typeof filter === 'string') {
            return this.sortAray(array, filter)
        } else {
            for (var i = filter.length -1; i >= 0; i--) {
                array = this.sortAray(array, filter[i]);

            return array;

    private sortAray(array, field) {
        return array.sort((a, b) => {
            if(typeof a[field] !== 'string') {
                a[field] !== b[field] ? a[field] < b[field] ? -1 : 1 : 0
            } else {
                a[field].toLowerCase() !== b[field].toLowerCase() ? a[field].toLowerCase() < b[field].toLowerCase() ? -1 : 1 : 0

How to convert List<string> to List<int>?


Removing single-quote from a string in php

$test = "{'employees':[{'firstName':'John', 'lastName':'Doe'},{'firstName':'John', 'lastName':'Doe'}]}" ; 
$test = str_replace("'", '"', $test);
echo   $test;
$jtest = json_decode($test,true);

to_string is not a member of std, says g++ (mingw)

This happened to me as well, I just wrote up a quick function rather than worrying about updating my compiler.

string to_string(int number){
    string number_string = "";
    char ones_char;
    int ones = 0;
        ones = number % 10;
            case 0: ones_char = '0'; break;
            case 1: ones_char = '1'; break;
            case 2: ones_char = '2'; break;
            case 3: ones_char = '3'; break;
            case 4: ones_char = '4'; break;
            case 5: ones_char = '5'; break;
            case 6: ones_char = '6'; break;
            case 7: ones_char = '7'; break;
            case 8: ones_char = '8'; break;
            case 9: ones_char = '9'; break;
            default : ErrorHandling("Trouble converting number to string.");
        number -= ones;
        number_string = ones_char + number_string;
        if(number == 0){
        number = number/10;
    return number_string;

How to convert .pfx file to keystore with private key?

Your PFX file should contain the private key within it. Export the private key and certificate directly from your PFX file (e.g. using OpenSSL) and import them into your Java keystore.


Further information:

  • Download OpenSSL for Windows here.
  • Export private key: openssl pkcs12 -in filename.pfx -nocerts -out key.pem
  • Export certificate: openssl pkcs12 -in filename.pfx -clcerts -nokeys -out cert.pem
  • Import private key and certificate into Java keystore using keytool.

how does unix handle full path name with space and arguments?

You can quote the entire path as in windows or you can escape the spaces like in:

/foo\ folder\ with\ space/ -help

Both ways will work!

Update MongoDB field using value of another field

Here's what we came up with for copying one field to another for ~150_000 records. It took about 6 minutes, but is still significantly less resource intensive than it would have been to instantiate and iterate over the same number of ruby objects.

js_query = %({
  $or : [
      'settings.mobile_notifications' : { $exists : false },
      'settings.mobile_admin_notifications' : { $exists : false }

js_for_each = %(function(user) {
  if (!user.settings.hasOwnProperty('mobile_notifications')) {
    user.settings.mobile_notifications = user.settings.email_notifications;
  if (!user.settings.hasOwnProperty('mobile_admin_notifications')) {
    user.settings.mobile_admin_notifications = user.settings.email_admin_notifications;

js = "db.users.find(#{js_query}).forEach(#{js_for_each});"
Mongoid::Sessions.default.command('$eval' => js)

What does <? php echo ("<pre>"); ..... echo("</pre>"); ?> mean?

I think you're talking about <pre></pre>. element is displayed in a fixed-width font, and it preserves both spaces and line breaks.

try printing an array with a **<pre>** and whitout **<pre>**

$arr = array(1, 2, 3);

echo '<pre>';
echo '</pre>';


Why dict.get(key) instead of dict[key]?

What is the dict.get() method?

As already mentioned the get method contains an additional parameter which indicates the missing value. From the documentation

get(key[, default])

Return the value for key if key is in the dictionary, else default. If default is not given, it defaults to None, so that this method never raises a KeyError.

An example can be

>>> d = {1:2,2:3}
>>> d[1]
>>> d.get(1)
>>> d.get(3)
>>> repr(d.get(3))
>>> d.get(3,1)

Are there speed improvements anywhere?

As mentioned here,

It seems that all three approaches now exhibit similar performance (within about 10% of each other), more or less independent of the properties of the list of words.

Earlier get was considerably slower, However now the speed is almost comparable along with the additional advantage of returning the default value. But to clear all our queries, we can test on a fairly large list (Note that the test includes looking up all the valid keys only)

def getway(d):
    for i in range(100):
        s = d.get(i)

def lookup(d):
    for i in range(100):
        s = d[i]

Now timing these two functions using timeit

>>> import timeit
>>> print(timeit.timeit("getway({i:i for i in range(100)})","from __main__ import getway"))
>>> print(timeit.timeit("lookup({i:i for i in range(100)})","from __main__ import lookup"))

As we can see the lookup is faster than the get as there is no function lookup. This can be seen through dis

>>> def lookup(d,val):
...     return d[val]
>>> def getway(d,val):
...     return d.get(val)
>>> dis.dis(getway)
  2           0 LOAD_FAST                0 (d)
              3 LOAD_ATTR                0 (get)
              6 LOAD_FAST                1 (val)
              9 CALL_FUNCTION            1
             12 RETURN_VALUE        
>>> dis.dis(lookup)
  2           0 LOAD_FAST                0 (d)
              3 LOAD_FAST                1 (val)
              6 BINARY_SUBSCR       
              7 RETURN_VALUE  

Where will it be useful?

It will be useful whenever you want to provide a default value whenever you are looking up a dictionary. This reduces

 if key in dic:
      val = dic[key]
      val = def_val

To a single line, val = dic.get(key,def_val)

Where will it be NOT useful?

Whenever you want to return a KeyError stating that the particular key is not available. Returning a default value also carries the risk that a particular default value may be a key too!

Is it possible to have get like feature in dict['key']?

Yes! We need to implement the __missing__ in a dict subclass.

A sample program can be

class MyDict(dict):
    def __missing__(self, key):
        return None

A small demonstration can be

>>> my_d = MyDict({1:2,2:3})
>>> my_d[1]
>>> my_d[3]
>>> repr(my_d[3])

make div's height expand with its content

Use the span tag with display:inline-block css attached to it. You can then use CSS and manipulate it like a div in lots of ways but if you don't include a width or height it expands and retracts based on its content.

Hope that helps.

Using CRON jobs to visit url?

* * * * * wget -O - >/dev/null 2>&1

That should work for you. Just have a wget script that loads the page.

Using -O - means that the output of the web request will be sent to STDOUT (standard output)

by adding >/dev/null we instruct standard output to be redirect to a black hole. by adding 2>&1 we instruct STDERR (errors) to also be sent to STDOUT, and thus all output will be sent to a blackhole. (so it will load the website, but never write a file anywhere)

Show animated GIF

For loading animated gifs stored in a source package (in the source code), this worked for me:

URL url = MyClass.class.getResource("/res/images/animated.gif");
ImageIcon imageIcon = new ImageIcon(url);
JLabel label = new JLabel(imageIcon);

Boto3 Error: botocore.exceptions.NoCredentialsError: Unable to locate credentials

Make sure your ~/.aws/credentials file in Unix looks like this:

aws_access_key_id = yourAccessId
aws_secret_access_key = yourSecretKey

aws_access_key_id = yourAccessId
aws_secret_access_key = yourSecretKey

Your Python script should look like this, and it'll work:

from __future__ import print_function
import boto3
import os

os.environ['AWS_PROFILE'] = "MyProfile1"
os.environ['AWS_DEFAULT_REGION'] = "us-east-1"

ec2 = boto3.client('ec2')

# Retrieves all regions/endpoints that work with EC2
response = ec2.describe_regions()
print('Regions:', response['Regions'])


jQuery Uncaught TypeError: Cannot read property 'fn' of undefined (anonymous function)

If you get Cannot read property 'fn' of undefined, the problem may be you loading libraries in wrong order.

For example:

You should load bootstrap.js first and then load bootstrap.js libraries.

<script src=""></script>
<script src=""></script>

UIButton Image + Text IOS

You should create custom imageview for image and custom label for text and you add to your button as subviews. That's it.

UIButton *yourButton = [UIButton buttonWithType:UIButtonTypeCustom];
yourButton.backgroundColor = [UIColor greenColor];
yourButton.frame = CGRectMake(140, 40, 175, 30);     
[yourButton addTarget:self action:@selector(yourButtonSelected:) forControlEvents:UIControlEventTouchUpInside]; 
[self.view addSubview:yourButton];

UIImageView *imageView1 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, yourButton.frame.size.width, yourButton.frame.size.height/2)];
imageView1.image =[UIImage imageNamed:@"images.jpg"];
[yourButton addSubview:imageView1];

UILabel *label=[[UILabel alloc] initWithFrame:CGRectMake(0, yourButton.frame.size.height/2, yourButton.frame.size.width, yourButton.frame.size.height/2)];
label.backgroundColor = [UIColor greenColor];
label.textAlignment= UITextAlignmentCenter;
label.text = @"ButtonTitle";
[yourButton addSubview:label];

For testing purpose, use yourButtonSelected: method

    NSLog(@"Your Button Selected");


I think it will be helpful to you.

Format numbers in django templates

The humanize solution is fine if your website is in English. For other languages, you need another solution: I recommend using Babel. One solution is to create a custom template tag to display numbers properly. Here's how: just create the following file in your_project/your_app/templatetags/

# -*- coding: utf-8 -*-
from django import template
from django.utils.translation import to_locale, get_language
from babel.numbers import format_number

register = template.Library()

def sexy_number(context, number, locale = None):
    if locale is None:
        locale = to_locale(get_language())
    return format_number(number, locale = locale)


Then you can use this template tag in your templates like this:

{% load sexy_number from sexify %}

{% sexy_number 1234.56 %}
  • For an american user (locale en_US) this displays 1,234.56.
  • For a french user (locale fr_FR), this displays 1 234,56.
  • ...

Of course you can use variables instead:

{% sexy_number some_variable %}

Note: the context parameter is currently not used in my example, but I put it there to show that you can easily tweak this template tag to make it use anything that's in the template context.

Assertion failure in dequeueReusableCellWithIdentifier:forIndexPath:

i had the same problem replacing with

static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

   if (cell==nil) {
        cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];



Vertically center text in a 100% height div?

Vertical align, dynamic height combined with absolute position is except some special conditions not possible without a few lines of JS (eg. jQuery). (can possibly be solved with backend code in some cases, or min-height combined with sensible top or margin styles, but not perfect)

I mostly only use absolute position when something is supposed to "popup" in relation to something else which is in the float, I think that's the best way to use it so you don't have to fiddle with things like this.

No offense, but most answers in here are way off.

How do I navigate to another page when PHP script is done?

if ($done)
    header("Location: /url/to/the/other/page");

How to get the first word of a sentence in PHP?

Even though it is little late, but PHP has one better solution for this:

$words=str_word_count($myvalue, 1);
echo $words[0];

How does the "position: sticky;" property work?

I have same problem, and i found the answer here.

If your element isn't sticking as expected the first thing to check are the rules applied to the container.

Specifically, look for any overflow property set on any parents of the element. You can't use: overflow: hidden, overflow: scroll or overflow: auto on the parent of a position: sticky element.

Convert JS Object to form data

Try obj2fd =>

import obj2fd from 'obj2fd'

let data = {a:1, b:2, c:{ca:1}};
let dataWithFormData = obj2fd(data);
//result => [a=>1, b=>2, c=>[ca=>1]]

Check if multiple strings exist in another string

The regex module recommended in python docs, supports this

words = {'he', 'or', 'low'}
p = regex.compile(r"\L<name>", name=words)
m = p.findall('helloworld')


['he', 'low', 'or']

Some details on implementation: link

List all kafka topics

Kafka requires zookeeper and indeed the list of topics is stored there, hence the kafka-topics tool needs to connect to zookeeper too. kafka-clients apis in the newer versions no longer talk to zookeeper directly, perhaps that's why you're under the impression a setup without zookeeper is possible. It is not, as kafka relies on it internally. For reference see: Step 2:

Kafka uses ZooKeeper so you need to first start a ZooKeeper server if you don't already have one

Check if the number is integer

Here's a solution using simpler functions and no hacks:

all.equal(a, as.integer(a))

What's more, you can test a whole vector at once, if you wish. Here's a function:

testInteger <- function(x){
  test <- all.equal(x, as.integer(x), check.attributes = FALSE)
  if(test == TRUE){ return(TRUE) }
  else { return(FALSE) }

You can change it to use *apply in the case of vectors, matrices, etc.

compareTo() vs. equals()

"equals" compare objects and return true or false and "compare to" return 0 if is true or an number [> 0] or [< 0] if is false here an example:

<!-- language: lang-java -->
//Objects Integer
Integer num1 = 1;
Integer num2 = 1;
//New Value
num2 = 3;//set value


num1.equals(num2) =true
num1.compareTo(num2) =0
num1.equals(num2) =false
num1.compareTo(num2) =-1

Documentation Compare to:

Documentation Equals :

How to copy part of an array to another array in C#?

See this question. LINQ Take() and Skip() are the most popular answers, as well as Array.CopyTo().

A purportedly faster extension method is described here.

How to install SQL Server Management Studio 2008 component only

SQL Server Management Studio 2008 R2 Express commandline:

The answer by dyslexicanaboko hits the crucial point, but this one is even simpler and suited for command line (unattended scenarios):

(tried out with SQL Server 2008 R2 Express, one instance installed and having downloaded SQLManagementStudio_x64_ENU.exe)

As pointed out in this thread often enough, it is better to use the original SQL server setup (e.g. SQL Express with Tools), if possible, but there are some scenarios, where you want to add SSMS at a SQL derivative without that tools, afterwards:

I´ve already put it in a batch syntax here:

@echo off


  1. For 2008 without R2 it should be enough to omit the /IACCEPTSQLSERVERLICENSETERMS flag, i guess.

  2. The /INDICATEPROGRESS parameter is useless here, the whole command takes a number of minutes and is 100% silent without any acknowledgement. Just look at the start menu, if the command is ready, if it has succeeded.

  3. This should work for the "ADV_SSMS" Feature (instead of "SSMS") too, which is the management studio extended variant (profiling, reporting, tuning, etc.)

LINQ: "contains" and a Lambda query

var depthead = (from s in db.M_Users
                  join m in db.M_User_Types on s.F_User_Type equals m.UserType_Id
                  where m.UserType_Name.ToUpper().Trim().Contains("DEPARTMENT HEAD")
                  select new {s.FullName,s.F_User_Type,s.userId,s.UserCode } 
               ).OrderBy(d => d.userId).ToList();

Model.AvailableDeptHead.Add(new SelectListItem { Text = "Select", Value = "0" });
for (int i = 0; i < depthead.Count; i++)
    Model.AvailableDeptHead.Add(new SelectListItem { Text = depthead[i].UserCode + " - " + depthead[i].FullName, Value = Convert.ToString(depthead[i].userId) });

Android Spinner : Avoid onItemSelected calls during initialization

To avoid calling spinner.setOnItemSelectedListener() during initialization

spinner.setSelection(Adapter.NO_SELECTION, true); //Add this line before setting listener
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {


    public void onNothingSelected(AdapterView<?> parent) {


Programmatically relaunch/recreate an activity?

If you're just looking to re-do your view, I had the exact same issue. In the onResume function try putting this:

mView = new AndroidPinballView(getApplication());

This was also in my onCreate(), so putting this in the onResume worked for me :)

Ansible: filter a list by its attributes

Not necessarily better, but since it's nice to have options here's how to do it using Jinja statements:

- debug:
    msg: "{% for address in network.addresses.private_man %}\
        {% if address.type == 'fixed' %}\
          {{ address.addr }}\
        {% endif %}\
      {% endfor %}"

Or if you prefer to put it all on one line:

- debug:
    msg: "{% for address in network.addresses.private_man if address.type == 'fixed' %}{{ address.addr }}{% endfor %}"

Which returns:

ok: [localhost] => {
    "msg": ""

How can I create a product key for my C# application?

You can do something like create a record which contains the data you want to authenticate to the application. This could include anything you want - e.g. program features to enable, expiry date, name of the user (if you want to bind it to a user). Then encrypt that using some crypto algorithm with a fixed key or hash it. Then you just verify it within your program. One way to distribute the license file (on windows) is to provide it as a file which updates the registry (saves the user having to type it).

Beware of false sense of security though - sooner or later someone will simply patch your program to skip that check, and distribute the patched version. Or, they will work out a key that passes all checks and distribute that, or backdate the clock, etc. It doesn't matter how convoluted you make your scheme, anything you do for this will ultimately be security through obscurity and they will always be able to this. Even if they can't someone will, and will distribute the hacked version. Same applies even if you supply a dongle - if someone wants to, they can patch out the check for that too. Digitally signing your code won't help, they can remove that signature, or resign it.

You can complicate matters a bit by using techniques to prevent the program running in a debugger etc, but even this is not bullet proof. So you should just make it difficult enough that an honest user will not forget to pay. Also be very careful that your scheme does not become obtrusive to paying users - it's better to have some ripped off copies than for your paying customers not to be able to use what they have paid for.

Another option is to have an online check - just provide the user with a unique ID, and check online as to what capabilities that ID should have, and cache it for some period. All the same caveats apply though - people can get round anything like this.

Consider also the support costs of having to deal with users who have forgotten their key, etc.

edit: I just want to add, don't invest too much time in this or think that somehow your convoluted scheme will be different and uncrackable. It won't, and cannot be as long as people control the hardware and OS your program runs on. Developers have been trying to come up with ever more complex schemes for this, thinking that if they develop their own system for it then it will be known only to them and therefore 'more secure'. But it really is the programming equivalent of trying to build a perpetual motion machine. :-)

CSS: 100% width or height while keeping aspect ratio?

Simple elegant working solution:

img {
  width: 600px;  /*width of parent container*/
  height: 350px; /*height of parent container*/
  object-fit: contain;
  position: relative;
  top: 50%;
  transform: translateY(-50%);

Stop a gif animation onload, on mouseover start the activation

I realise this answer is late, but I found a rather simple, elegant, and effective solution to this problem and felt it necessary to post it here.

However one thing I feel I need to make clear is that this doesn't start gif animation on mouseover, pause it on mouseout, and continue it when you mouseover it again. That, unfortunately, is impossible to do with gifs. (It is possible to do with a string of images displayed one after another to look like a gif, but taking apart every frame of your gifs and copying all those urls into a script would be time consuming)

What my solution does is make an image looks like it starts moving on mouseover. You make the first frame of your gif an image and put that image on the webpage then replace the image with the gif on mouseover and it looks like it starts moving. It resets on mouseout.

Just insert this script in the head section of your HTML:

            $(this).attr("src", "GIF URL HERE");
            $(this).attr("src", "STATIC IMAGE URL HERE");

And put this code in the img tag of the image you want to animate.


This will load the gif on mouseover, so it will seem like your image starts moving. (This is better than loading the gif onload because then the transition from static image to gif is choppy because the gif will start on a random frame)

for more than one image just recreate the script create a function:

<script type="text/javascript">

var staticGifSuffix = "-static.gif";
var gifSuffix = ".gif";

$(document).ready(function() {

  $(".img-animate").each(function () {

            var originalSrc = $(this).attr("src");
            $(this).attr("src", originalSrc.replace(staticGifSuffix, gifSuffix));
            var originalSrc = $(this).attr("src");
            $(this).attr("src", originalSrc.replace(gifSuffix, staticGifSuffix));  




<img class="img-animate" src="example-static.gif" >
<img class="img-animate" src="example-static.gif" >
<img class="img-animate" src="example-static.gif" >
<img class="img-animate" src="example-static.gif" >
<img class="img-animate" src="example-static.gif" >


That code block is a functioning web page (based on the information you have given me) that will display the static images and on hover, load and display the gif's. All you have to do is insert the url's for the static images.

Capture HTML Canvas as gif/jpg/png/pdf?

You can use jspdf to capture a canvas into an image or pdf like this:

var imgData = canvas.toDataURL('image/png');              
var doc = new jsPDF('p', 'mm');
doc.addImage(imgData, 'PNG', 10, 10);'sample-file.pdf');

More info:

How to specify a local file within html using the file: scheme?

For apache look up SymLink or you can solve via the OS with Symbolic Links or on linux set up a library link/etc

My answer is one method specifically to windows 10.

So my method involves mapping a network drive to U:/ (e.g. I use G:/ for Google Drive)

open cmd and type hostname (example result: LAPTOP-G666P000, you could use your ip instead, but using a static hostname for identifying yourself makes more sense if your network stops)

Press Windows_key + E > right click 'This PC' > press N (It's Map Network drive, NOT add a network location)

If you are right clicking the shortcut on the desktop you need to press N then enter

Fill out U: or G: or Z: or whatever you want Example Address: \\LAPTOP-G666P000\c$\Users\username\

Then you can use <a href="file:///u:/2ndFile.html"><button type="submit">Local file</button> like in your question

related: You can also use this method for FTPs, and setup multiple drives for different relative paths on that same network.

related2: I have used http://localhost/c$ etc before on some WAMP/apache servers too before, you can use .htaccess for control/security but I recommend to not do so on a live/production machine -- or any other symlink documentroot example you can google

How to append data to a json file?

Append entry to the file contents if file exists, otherwise append the entry to an empty list and write in in the file:

a = []
if not os.path.isfile(fname):
    with open(fname, mode='w') as f:
        f.write(json.dumps(a, indent=2))
    with open(fname) as feedsjson:
        feeds = json.load(feedsjson)

    with open(fname, mode='w') as f:
        f.write(json.dumps(feeds, indent=2))

Insert string in beginning of another string

import java.lang.StringBuilder;

public class Program {
    public static void main(String[] args) {

    // Create a new StringBuilder.
    StringBuilder builder = new StringBuilder();

    // Loop and append values.
    for (int i = 0; i < 5; i++) {
        builder.append("abc ");
    // Convert to string.
    String result = builder.toString();

    // Print result.

Can overridden methods differ in return type?

The other answers are all correct, but surprisingly all leaving out the theoretical aspect here: return types can be different, but they can only restrict the type used in the super class because of the Liskov Substitution Principle.

It is super simple: when you have "client" code that calls some method:

int foo =;

then the above has to work (and return something that is an int no matter which implementation of bar() is invoked).

Meaning: if there is a Bar subclass that overrides bar() then you still have to return something that doesn't break "caller code".

In other words: assume that the base bar() is supposed to return int. Then a subclass could return short - but not long because callers will be fine dealing with a short value, but not a long!

ssh connection refused on Raspberry Pi

I think pi has ssh server enabled by default. Mine have always worked out of the box. Depends which operating system version maybe.

Most of the time when it fails for me it is because the ip address has been changed. Perhaps you are pinging something else now? Also sometimes they just refuse to connect and need a restart.

String comparison in Python: is vs. ==

See This question

Your logic in reading

For all built-in Python objects (like strings, lists, dicts, functions, etc.), if x is y, then x==y is also True.

is slightly flawed.

If is applies then == will be True, but it does NOT apply in reverse. == may yield True while is yields False.

How to comment and uncomment blocks of code in the Office VBA Editor

Have you checked MZTools?? It does a lot of cool stuff...

If I'm not wrong, one of the functionalities it offers is to set your own shortcuts.

Moving Panel in Visual Studio Code to right side

As of June 2019 this setting can be found through searching 'Panel' - if you want to change the default there is an option for it as shown in the screenshot:enter image description here

Select N random elements from a List<T> in C#

public static IEnumerable<T> GetRandom<T>(this IList<T> list, int count, Random random)
        // Probably you should throw exception if count > list.Count
        count = Math.Min(list.Count, count);

        var selectedIndices = new SortedSet<int>();

        // Random upper bound
        int randomMax = list.Count - 1;

        while (selectedIndices.Count < count)
            int randomIndex = random.Next(0, randomMax);

            // skip over already selected indeces
            foreach (var selectedIndex in selectedIndices)
                if (selectedIndex <= randomIndex)

            yield return list[randomIndex];


Memory: ~count
Complexity: O(count2)

Are multiple `.gitignore`s frowned on?

Pro single

  • Easy to find.

  • Hunting down exclusion rules can be quite difficult if I have multiple gitignore, at several levels in the repo.

  • With multiple files, you also typically wind up with a fair bit of duplication.

Pro multiple

  • Scopes "knowledge" to the part of the file tree where it is needed.

  • Since Git only tracks files, an empty .gitignore is the only way to commit an "empty" directory.

    (And before Git 1.8, the only way to exclude a pattern like my/**.example was to create my/.gitignore in with the pattern **.foo. This reason doesn't apply now, as you can do /my/**/*.example.)

I much prefer a single file, where I can find all the exclusions. I've never missed per-directory .svn, and I won't miss per-directory .gitignore either.

That said, multiple gitignores are quite common. If you do use them, at least be consistent in their use to make them reasonable to work with. For example, you may put them in directories only one level from the root.

How do I create a crontab through a script

In Ubuntu and many other distros, you can just put a file into the /etc/cron.d directory containing a single line with a valid crontab entry. No need to add a line to an existing file.

If you just need something to run daily, just put a file into /etc/cron.daily. Likewise, you can also drop files into /etc/cron.hourly, /etc/cron.monthly, and /etc/cron.weekly.

Right align and left align text in same HTML table cell

If you want them on separate lines do what Balon said. If you want them on the same lines, do:

  <div style="float:left;width:50%;">this is left</div>
  <div style="float:right;width:50%;">this is right</div>

How to strip comma in Python string

unicode('foo,bar').translate(dict([[ord(char), u''] for char in u',']))

Python: avoid new line with print command

In Python 3.x, you can use the end argument to the print() function to prevent a newline character from being printed:

print("Nope, that is not a two. That is a", end="")

In Python 2.x, you can use a trailing comma:

print "this should be",
print "on the same line"

You don't need this to simply print a variable, though:

print "Nope, that is not a two. That is a", x

Note that the trailing comma still results in a space being printed at the end of the line, i.e. it's equivalent to using end=" " in Python 3. To suppress the space character as well, you can either use

from __future__ import print_function

to get access to the Python 3 print function or use sys.stdout.write().

JFrame in full screen Java

you can simply do like this -

public void FullScreen() {
        if (Build.VERSION.SDK_INT > 11 && Build.VERSION.SDK_INT < 19) {
            final View v = this.activity.getWindow().getDecorView();
        else if (Build.VERSION.SDK_INT >= 19) {
            final View decorView = this.activity.getWindow().getDecorView();
            final int uiOptions = 4102;

How to find Port number of IP address?

Quite an old question, but might be helpful to somebody in need.

If you know the url, 1. open the chrome browser, 2. open developer tools in chrome , 3. Put the url in search bar and hit enter 4. look in network tab, you will see the ip and port both

How to press back button in android programmatically?

Simply add finish(); in your first class' (login activity) onPause(); method. that's all

MySQL: Can't create table (errno: 150)

A real edge case is where you have used an MySQL tool, (Sequel Pro in my case) to rename a database. Then created a database with the same name.

This kept foreign key constraints to the same database name, so the renamed database (e.g. my_db_renamed) had foreign key constraints in the newly created database (my_db)

Not sure if this is a bug in Sequel Pro, or if some use case requires this behaviour, but it cost me best part of a morning :/

Getting file names without extensions

Use Path.GetFileNameWithoutExtension. Path is in System.IO namespace.

How to fix the Hibernate "object references an unsaved transient instance - save the transient instance before flushing" error

Don't use Cascade.All until you really have to. Role and Permission have bidirectional manyToMany relation. Then the following code would work fine

    Permission p = new Permission();
    Permission p2 = new Permission();
    p = (Permission); // returned p has id filled in.
    p2 = (Permission); // so does p2.
    Role role = new Role();
    role.setDescription("a test role");
    List<Permission> pList = new ArrayList<Permission>();

while if the object is just a "new" one, then it would throw the same error.

Name node is in safe mode. Not able to leave

try this, it will work

sudo -u hdfs hdfs dfsadmin -safemode leave

Git merge error "commit is not possible because you have unmerged files"

You need to do two things. First add the changes with

git add .
git stash  

git checkout <some branch>

It should solve your issue as it solved to me.

changing visibility using javascript

Use display instead of visibility. display: none for invisible and no setting for visible.

Useful example of a shutdown hook in Java?

You could do the following:

  • Let the shutdown hook set some AtomicBoolean (or volatile boolean) "keepRunning" to false
  • (Optionally, .interrupt the working threads if they wait for data in some blocking call)
  • Wait for the working threads (executing writeBatch in your case) to finish, by calling the Thread.join() method on the working threads.
  • Terminate the program

Some sketchy code:

  • Add a static volatile boolean keepRunning = true;
  • In run() you change to

    for (int i = 0; i < N && keepRunning; ++i)
        writeBatch(pw, i);
  • In main() you add:

    final Thread mainThread = Thread.currentThread();
    Runtime.getRuntime().addShutdownHook(new Thread() {
        public void run() {
            keepRunning = false;

That's roughly how I do a graceful "reject all clients upon hitting Control-C" in terminal.

From the docs:

When the virtual machine begins its shutdown sequence it will start all registered shutdown hooks in some unspecified order and let them run concurrently. When all the hooks have finished it will then run all uninvoked finalizers if finalization-on-exit has been enabled. Finally, the virtual machine will halt.

That is, a shutdown hook keeps the JVM running until the hook has terminated (returned from the run()-method.

$(document).ready shorthand

The correct shorthand is this:

$(function() {
    // this behaves as if within document.ready

The code you posted…


//some code


…creates an anonymous function and executes it immediately with jQuery being passed in as the arg $. All it effectively does is take the code inside the function and execute it like normal, since $ is already an alias for jQuery. :D

Easiest way to flip a boolean value?

Just because I like to question code. I propose that you can also make use of the ternary by doing something like this:


bool flipValue = false;
bool bShouldFlip = true;
flipValue = bShouldFlip ? !flipValue : flipValue;

Proper way to make HTML nested list?

Option 2 is correct: The nested <ul> is a child of the <li> it belongs in.

If you validate, option 1 comes up as an error in html 5 -- credit: user3272456

Correct: <ul> as child of <li>

The proper way to make HTML nested list is with the nested <ul> as a child of the <li> to which it belongs. The nested list should be inside of the <li> element of the list in which it is nested.


W3C Standard for Nesting Lists

A list item can contain another entire list — this is known as "nesting" a list. It is useful for things like tables of contents, such as the one at the start of this article:

  1. Chapter One
    1. Section One
    2. Section Two
    3. Section Three
  2. Chapter Two
  3. Chapter Three

The key to nesting lists is to remember that the nested list should relate to one specific list item. To reflect that in the code, the nested list is contained inside that list item. The code for the list above looks something like this:

  <li>Chapter One
      <li>Section One</li>
      <li>Section Two </li>
      <li>Section Three </li>
  <li>Chapter Two</li>
  <li>Chapter Three  </li>

Note how the nested list starts after the <li> and the text of the containing list item (“Chapter One”); then ends before the </li> of the containing list item. Nested lists often form the basis for website navigation menus, as they are a good way to define the hierarchical structure of the website.

Theoretically you can nest as many lists as you like, although in practice it can become confusing to nest lists too deeply. For very large lists, you may be better off splitting the content up into several lists with headings instead, or even splitting it up into separate pages.

System.Data.SqlClient.SqlException: Login failed for user

Numpty here used SQL authentication

enter image description here

instead of Windows (correct)

enter image description here

when adding the login to SQL Server, which also gives you this error if you are using Windows auth.

How to add elements of a string array to a string array list?

Arrays.asList is the handy function available in Java to convert an array variable to List or Collection. For better under standing consider the below example:


import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Wetland {
    private String name;
    private List<String> species = new ArrayList<String>();

    public Wetland(String name, String[] speciesArr) { = name;
        this.species = Arrays.asList(speciesArr);

    public void display() {
        System.out.println("Name: " + name);
        System.out.println("Elements in the List");
        for (String string : species) {

     * @Description: Method to test your code
    public static void main(String[] args) {
        String name = "Colors";
        String speciesArr[] = new String [] {"red", "blue", "green"};
        Wetland wetland = new Wetland(name, speciesArr);



enter image description here

Get div tag scroll position using JavaScript

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<html xmlns="">
<head runat="server">
    <script type="text/javascript">
        function scollPos() {
            var div = document.getElementById("myDiv").scrollTop;
            document.getElementById("pos").innerHTML = div;
    <form id="form1">
    <div id="pos">
    <div id="myDiv" style="overflow: auto; height: 200px; width: 200px;" onscroll="scollPos();">
        Place some large content here

Java Wait and Notify: IllegalMonitorStateException

You're calling both wait and notifyAll without using a synchronized block. In both cases the calling thread must own the lock on the monitor you call the method on.

From the docs for notify (wait and notifyAll have similar documentation but refer to notify for the fullest description):

This method should only be called by a thread that is the owner of this object's monitor. A thread becomes the owner of the object's monitor in one of three ways:

  • By executing a synchronized instance method of that object.
  • By executing the body of a synchronized statement that synchronizes on the object.
  • For objects of type Class, by executing a synchronized static method of that class.

Only one thread at a time can own an object's monitor.

Only one thread will be able to actually exit wait at a time after notifyAll as they'll all have to acquire the same monitor again - but all will have been notified, so as soon as the first one then exits the synchronized block, the next will acquire the lock etc.

Error: org.testng.TestNGException: Cannot find class in classpath: EmpClass

I also had this issue. I'm using IntelliJ IDEA. I was using src/main/java for configuration files and src/test/java for test files.
Because of this testNG couldn't find the class path. To prevent getting that error need to move all the files from src/main/java to src/test/java or vice versa.

Inverse dictionary lookup in Python

No, you can not do this efficiently without looking in all the keys and checking all their values. So you will need O(n) time to do this. If you need to do a lot of such lookups you will need to do this efficiently by constructing a reversed dictionary (can be done also in O(n)) and then making a search inside of this reversed dictionary (each search will take on average O(1)).

Here is an example of how to construct a reversed dictionary (which will be able to do one to many mapping) from a normal dictionary:

for i in h_normal:
    for j in h_normal[i]:
        if j not in h_reversed:
            h_reversed[j] = set([i])

For example if your

h_normal = {
  1: set([3]), 
  2: set([5, 7]), 
  3: set([]), 
  4: set([7]), 
  5: set([1, 4]), 
  6: set([1, 7]), 
  7: set([1]), 
  8: set([2, 5, 6])

your h_reversed will be

  1: set([5, 6, 7]),
  2: set([8]), 
  3: set([1]), 
  4: set([5]), 
  5: set([8, 2]), 
  6: set([8]), 
  7: set([2, 4, 6])

How can I generate Javadoc comments in Eclipse?

You mean menu Project -> Generate Javadoc ?

How to delete a file after checking whether it exists

If you are reading from that file using FileStream and then wanting to delete it, make sure you close the FileStream before you call the File.Delete(path). I had this issue.

var filestream = new System.IO.FileStream(@"C:\Test\PutInv.txt", System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.ReadWrite);

MongoDB: How to find out if an array field contains an element?

It seems like the $in operator would serve your purposes just fine.

You could do something like this (pseudo-query):

if ({"students" : {"$in" : [studentId]}, "course" : courseId }).count() > 0) {
  // student is enrolled in class

Alternatively, you could remove the "course" : courseId clause and get back a set of all classes the student is enrolled in.

Unicode via CSS :before

At first link fontwaesome CSS file in your HTML file then create an after or before pseudo class like "font-family: "FontAwesome"; content: "\f101";" then save. I hope this work good.

how to concatenate two dictionaries to create a new one in Python?

d4 = dict(d1.items() + d2.items() + d3.items())

alternatively (and supposedly faster):

d4 = dict(d1)

Previous SO question that both of these answers came from is here.

Port 80 is being used by SYSTEM (PID 4), what is that?

This Process works for me:

  1. Right click on My Computer.
  2. Select Manage.
  3. Double click Services and Applications.
  4. Then double-click Services.
  5. Right click on "World Wide Web Publishing Service".
  6. Select Stop
  7. Restart XAMPP

What is "runtime"?

a runtime could denote the current phase of program life (runtime / compile time / load time / link time) or it could mean a runtime library, which form the basic low level actions that interface with the execution environment. or it could mean a runtime system, which is the same as an execution environment.

in the case of C programs, the runtime is the code that sets up the stack, the heap etc. which a requirement expected by the C environment. it essentially sets up the environment that is promised by the language. (it could have a runtime library component, crt0.lib or something like that in case of C)

How to make a function wait until a callback has been called using node.js

Note: This answer should probably not be used in production code. It's a hack and you should know about the implications.

There is the uvrun module (updated for newer Nodejs versions here) where you can execute a single loop round of the libuv main event loop (which is the Nodejs main loop).

Your code would look like this:

function(query) {
  var r;
  myApi.exec('SomeCommand', function(response) {
    r = response;
  var uvrun = require("uvrun");
  while (!r)
  return r;

(You might alternative use uvrun.runNoWait(). That could avoid some problems with blocking, but takes 100% CPU.)

Note that this approach kind of invalidates the whole purpose of Nodejs, i.e. to have everything async and non-blocking. Also, it could increase your callstack depth a lot, so you might end up with stack overflows. If you run such function recursively, you definitely will run into troubles.

See the other answers about how to redesign your code to do it "right".

This solution here is probably only useful when you do testing and esp. want to have synced and serial code.

css display table cell requires percentage width

You just need to add 'table-layout: fixed;'

.table {
   display: table;
   height: 100px;
   width: 100%;
   table-layout: fixed;

How do I set the focus to the first input element in an HTML form independent from the id?

You also need to skip any hidden inputs.

for (var i = 0; document.forms[0].elements[i].type == 'hidden'; i++);

ESRI : Failed to parse source map

I had the same problem because .htaccess has incorrect settings:

RewriteEngine on
RewriteRule !.(js|gif|jpg|png|css)$ index.php

I solved this by modifying the file:

RewriteEngine on
RewriteRule !.(js|gif|jpg|png|css|eot|svg|ttf|woff|woff2|map)$ index.php

Finding non-numeric rows in dataframe in pandas?

# Original code
df = pd.DataFrame({'a': [1, 2, 3, 'bad', 5],
                   'b': [0.1, 0.2, 0.3, 0.4, 0.5],
                   'item': ['a', 'b', 'c', 'd', 'e']})
df = df.set_index('item')

Convert to numeric using 'coerce' which fills bad values with 'nan'

a = pd.to_numeric(df.a, errors='coerce')

Use isna to return a boolean index:

idx = a.isna()

Apply that index to the data frame:



Returns the row with the bad data in it:

        a    b
d     bad  0.4

Set port for php artisan.php serve

you can also add host as well with same command like :

php artisan serve --host= --port=8080

Android Log.v(), Log.d(), Log.i(), Log.w(), Log.e() - When to use each one?

Let's go in reverse order:

  • Log.e: This is for when bad stuff happens. Use this tag in places like inside a catch statement. You know that an error has occurred and therefore you're logging an error.

  • Log.w: Use this when you suspect something shady is going on. You may not be completely in full on error mode, but maybe you recovered from some unexpected behavior. Basically, use this to log stuff you didn't expect to happen but isn't necessarily an error. Kind of like a "hey, this happened, and it's weird, we should look into it."

  • Log.i: Use this to post useful information to the log. For example: that you have successfully connected to a server. Basically use it to report successes.

  • Log.d: Use this for debugging purposes. If you want to print out a bunch of messages so you can log the exact flow of your program, use this. If you want to keep a log of variable values, use this.

  • Log.v: Use this when you want to go absolutely nuts with your logging. If for some reason you've decided to log every little thing in a particular part of your app, use the Log.v tag.

And as a bonus...

  • Use this when stuff goes absolutely, horribly, holy-crap wrong. You know those catch blocks where you're catching errors that you never should get...yeah, if you wanna log them use

How do I replace whitespaces with underscore?

mystring.replace (" ", "_")

if you assign this value to any variable, it will work

s = mystring.replace (" ", "_")

by default mystring wont have this

How do I create a dynamic key to be added to a JavaScript object variable

Square brackets:

jsObj['key' + i] = 'example' + 1;

In JavaScript, all arrays are objects, but not all objects are arrays. The primary difference (and one that's pretty hard to mimic with straight JavaScript and plain objects) is that array instances maintain the length property so that it reflects one plus the numeric value of the property whose name is numeric and whose value, when converted to a number, is the largest of all such properties. That sounds really weird, but it just means that given an array instance, the properties with names like "0", "5", "207", and so on, are all treated specially in that their existence determines the value of length. And, on top of that, the value of length can be set to remove such properties. Setting the length of an array to 0 effectively removes all properties whose names look like whole numbers.

OK, so that's what makes an array special. All of that, however, has nothing at all to do with how the JavaScript [ ] operator works. That operator is an object property access mechanism which works on any object. It's important to note in that regard that numeric array property names are not special as far as simple property access goes. They're just strings that happen to look like numbers, but JavaScript object property names can be any sort of string you like.

Thus, the way the [ ] operator works in a for loop iterating through an array:

for (var i = 0; i < myArray.length; ++i) {
  var value = myArray[i]; // property access
  // ...

is really no different from the way [ ] works when accessing a property whose name is some computed string:

var value = jsObj["key" + i];

The [ ] operator there is doing precisely the same thing in both instances. The fact that in one case the object involved happens to be an array is unimportant, in other words.

When setting property values using [ ], the story is the same except for the special behavior around maintaining the length property. If you set a property with a numeric key on an array instance:

myArray[200] = 5;

then (assuming that "200" is the biggest numeric property name) the length property will be updated to 201 as a side-effect of the property assignment. If the same thing is done to a plain object, however:

myObj[200] = 5;

there's no such side-effect. The property called "200" of both the array and the object will be set to the value 5 in otherwise the exact same way.

One might think that because that length behavior is kind-of handy, you might as well make all objects instances of the Array constructor instead of plain objects. There's nothing directly wrong about that (though it can be confusing, especially for people familiar with some other languages, for some properties to be included in the length but not others). However, if you're working with JSON serialization (a fairly common thing), understand that array instances are serialized to JSON in a way that only involves the numerically-named properties. Other properties added to the array will never appear in the serialized JSON form. So for example:

var obj = [];
obj[0] = "hello world";
obj["something"] = 5000;

var objJSON = JSON.stringify(obj);

the value of "objJSON" will be a string containing just ["hello world"]; the "something" property will be lost.


If you're able to use ES6 JavaScript features, you can use Computed Property Names to handle this very easily:

var key = 'DYNAMIC_KEY',
    obj = {
        [key]: 'ES6!'

// > { 'DYNAMIC_KEY': 'ES6!' }

Getting all selected checkboxes in an array

Using Jquery

You only need to add class to every input, i have add class "source" you can change it of course

<input class="source" type="checkbox" name="type" value="4" />
<input class="source" type="checkbox" name="type" value="3" />
<input class="source" type="checkbox" name="type" value="1" />
<input class="source" type="checkbox" name="type" value="5" />

<script type="text/javascript">
$(document).ready(function() {
    var selected_value = []; // initialize empty array 
    console.log(selected_value); //Press F12 to see all selected values

returning a Void object

If you just don't need anything as your type, you can use void. This can be used for implementing functions, or actions. You could then do something like this:

interface Action<T> {
    public T execute();

abstract class VoidAction implements Action<Void> {
    public Void execute() {
        return null;

    abstract void executeInternal();

Or you could omit the abstract class, and do the return null in every action that doesn't require a return value yourself.

You could then use those actions like this:

Given a method

private static <T> T executeAction(Action<T> action) {
    return action.execute();

you can call it like

String result = executeAction(new Action<String>() {
    public String execute() {
        //code here
        return "Return me!";

or, for the void action (note that you're not assigning the result to anything)

executeAction(new VoidAction() {
    public void executeInternal() {
        //code here

How to fix '.' is not an internal or external command error

Just leave out the "dot-slash" ./:

D:\Gesture Recognition\Gesture Recognition\Debug>"Gesture Recognition.exe"

Though, if you wanted to, you could use .\ and it would work.

D:\Gesture Recognition\Gesture Recognition\Debug>.\"Gesture Recognition.exe"

Manage toolbar's navigation and back button from fragment in android

(Kotlin) In the activity hosting the fragment(s):

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
    when (item.itemId) { -> {
            return true
    return super.onOptionsItemSelected(item)

I have found that when I add fragments to a project, they show the action bar home button by default, to remove/disable it put this in onViewCreated() (use true to enable it if it is not showing):

val actionBar = this.requireActivity().actionBar

How is length implemented in Java Arrays?

You're correct, length is a data member, not a method.

From the Arrays tutorial:

The length of an array is established when the array is created. After creation, its length is fixed.

Google Play Services Missing in Emulator (Android 4.4.2)

google play service is just a library to create application but in order to use application that use google play service library , you need to install google play in your emulator.and for that it need the unique device id. and device id is only on the real device not have on emulator. so for testing it , you need real android device.

Center div on the middle of screen

Try this:

    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -50px;
    margin-left: -50px;
    width: 100px;
    height: 100px;
    background: red;

Here div is html tag. You wrote a html tag followed by a dot that is wrong.Only a class is written followed by dot.

How to force file download with PHP

header("Content-Type: application/octet-stream");
header("Content-Transfer-Encoding: Binary");
header("Content-disposition: attachment; filename=\"file.exe\""); 
echo readfile($url);

is correct

or better one for exe type of files

header("Location: $url");

Does the Java &= operator apply & or &&?

see 15.22.2 of the JLS. For boolean operands, the & operator is boolean, not bitwise. The only difference between && and & for boolean operands is that for && it is short circuited (meaning that the second operand isn't evaluated if the first operand evaluates to false).

So in your case, if b is a primitive, a = a && b, a = a & b, and a &= b all do the same thing.

What's the difference between ASCII and Unicode?

java provides support for Unicode i.e it supports all world wide alphabets. Hence the size of char in java is 2 bytes. And range is 0 to 65535.

enter image description here

Can I rollback a transaction I've already committed? (data loss)

No, you can't undo, rollback or reverse a commit.


(Note: if you deleted the data directory off the filesystem, do NOT stop the database. The following advice applies to an accidental commit of a DELETE or similar, not an rm -rf /data/directory scenario).

If this data was important, STOP YOUR DATABASE NOW and do not restart it. Use pg_ctl stop -m immediate so that no checkpoint is run on shutdown.

You cannot roll back a transaction once it has commited. You will need to restore the data from backups, or use point-in-time recovery, which must have been set up before the accident happened.

If you didn't have any PITR / WAL archiving set up and don't have backups, you're in real trouble.

Urgent mitigation

Once your database is stopped, you should make a file system level copy of the whole data directory - the folder that contains base, pg_clog, etc. Copy all of it to a new location. Do not do anything to the copy in the new location, it is your only hope of recovering your data if you do not have backups. Make another copy on some removable storage if you can, and then unplug that storage from the computer. Remember, you need absolutely every part of the data directory, including pg_xlog etc. No part is unimportant.

Exactly how to make the copy depends on which operating system you're running. Where the data dir is depends on which OS you're running and how you installed PostgreSQL.

Ways some data could've survived

If you stop your DB quickly enough you might have a hope of recovering some data from the tables. That's because PostgreSQL uses multi-version concurrency control (MVCC) to manage concurrent access to its storage. Sometimes it will write new versions of the rows you update to the table, leaving the old ones in place but marked as "deleted". After a while autovaccum comes along and marks the rows as free space, so they can be overwritten by a later INSERT or UPDATE. Thus, the old versions of the UPDATEd rows might still be lying around, present but inaccessible.

Additionally, Pg writes in two phases. First data is written to the write-ahead log (WAL). Only once it's been written to the WAL and hit disk, it's then copied to the "heap" (the main tables), possibly overwriting old data that was there. The WAL content is copied to the main heap by the bgwriter and by periodic checkpoints. By default checkpoints happen every 5 minutes. If you manage to stop the database before a checkpoint has happened and stopped it by hard-killing it, pulling the plug on the machine, or using pg_ctl in immediate mode you might've captured the data from before the checkpoint happened, so your old data is more likely to still be in the heap.

Now that you have made a complete file-system-level copy of the data dir you can start your database back up if you really need to; the data will still be gone, but you've done what you can to give yourself some hope of maybe recovering it. Given the choice I'd probably keep the DB shut down just to be safe.


You may now need to hire an expert in PostgreSQL's innards to assist you in a data recovery attempt. Be prepared to pay a professional for their time, possibly quite a bit of time.

I posted about this on the Pg mailing list, and ?????? ?????? linked to depesz's post on pg_dirtyread, which looks like just what you want, though it doesn't recover TOASTed data so it's of limited utility. Give it a try, if you're lucky it might work.

See: pg_dirtyread on GitHub.

I've removed what I'd written in this section as it's obsoleted by that tool.

See also PostgreSQL row storage fundamentals


See my blog entry Preventing PostgreSQL database corruption.

On a semi-related side-note, if you were using two phase commit you could ROLLBACK PREPARED for a transction that was prepared for commit but not fully commited. That's about the closest you get to rolling back an already-committed transaction, and does not apply to your situation.

TypeScript and React - children type?

I'm using the following

type Props = { children: React.ReactNode };

const MyComponent: React.FC<Props> = ({children}) => {
  return (
      { children }

export default MyComponent;

How do I parse command line arguments in Bash?

  • Use enhanced getopt from util-linux or formerly GNU glibc.1
  • It works with getopt_long() the C function of GNU glibc.
  • Has all useful distinguishing features (the others don’t have them):
    • handles spaces, quoting characters and even binary in arguments2 (non-enhanced getopt can’t do this)
    • it can handle options at the end: -o outFile file1 file2 -v (getopts doesn’t do this)
    • allows =-style long options: --outfile=fileOut --infile fileIn (allowing both is lengthy if self parsing)
    • allows combined short options, e.g. -vfd (real work if self parsing)
    • allows touching option-arguments, e.g. -oOutfile or -vfdoOutfile
  • Is so old already3 that no GNU system is missing this (e.g. any Linux has it).
  • You can test for its existence with: getopt --test ? return value 4.
  • Other getopt or shell-builtin getopts are of limited use.

The following calls

myscript -vfd ./foo/bar/someFile -o /fizz/someOtherFile
myscript -v -f -d -o/fizz/someOtherFile -- ./foo/bar/someFile
myscript --verbose --force --debug ./foo/bar/someFile -o/fizz/someOtherFile
myscript --output=/fizz/someOtherFile ./foo/bar/someFile -vfd
myscript ./foo/bar/someFile -df -v --output /fizz/someOtherFile

all return

verbose: y, force: y, debug: y, in: ./foo/bar/someFile, out: /fizz/someOtherFile

with the following myscript

# saner programming env: these switches turn some bugs into errors
set -o errexit -o pipefail -o noclobber -o nounset

# -allow a command to fail with !’s side effect on errexit
# -use return value from ${PIPESTATUS[0]}, because ! hosed $?
! getopt --test > /dev/null 
if [[ ${PIPESTATUS[0]} -ne 4 ]]; then
    echo 'I’m sorry, `getopt --test` failed in this environment.'
    exit 1


# -regarding ! and PIPESTATUS see above
# -temporarily store output to be able to check for errors
# -activate quoting/enhanced mode (e.g. by writing out “--options”)
# -pass arguments only via   -- "$@"   to separate them correctly
! PARSED=$(getopt --options=$OPTIONS --longoptions=$LONGOPTS --name "$0" -- "$@")
if [[ ${PIPESTATUS[0]} -ne 0 ]]; then
    # e.g. return value is 1
    #  then getopt has complained about wrong arguments to stdout
    exit 2
# read getopt’s output this way to handle the quoting right:
eval set -- "$PARSED"

d=n f=n v=n outFile=-
# now enjoy the options in order and nicely split until we see --
while true; do
    case "$1" in
            shift 2
            echo "Programming error"
            exit 3

# handle non-option arguments
if [[ $# -ne 1 ]]; then
    echo "$0: A single input file is required."
    exit 4

echo "verbose: $v, force: $f, debug: $d, in: $1, out: $outFile"

1 enhanced getopt is available on most “bash-systems”, including Cygwin; on OS X try brew install gnu-getopt or sudo port install getopt
2 the POSIX exec() conventions have no reliable way to pass binary NULL in command line arguments; those bytes prematurely end the argument
3 first version released in 1997 or before (I only tracked it back to 1997)

Rollback one specific migration in Laravel

If you want modify original migration file and migrate it again, you can use this package to migrate. (Applicable to Laravel 5.4 or later)

First, install package in your Laravel project:

composer require caloskao/migrate-specific

Register command at app/Console/Kernel.php :

protected $commands = [

Now, run this command to migrate your file

php artisan migrate:specific database/migrations/table.php

What's the foolproof way to tell which version(s) of .NET are installed on a production Windows Server?

To get the installed dotnet version,
Create a Console app. Add this class Run that

using Microsoft.Win32;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication2
    public class GetDotNetVersion
        public static void Get45PlusFromRegistry()
            const string subkey = @"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\";
            using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(subkey))
                if (ndpKey != null && ndpKey.GetValue("Release") != null)
                    Console.WriteLine(".NET Framework Version: " + CheckFor45PlusVersion((int)ndpKey.GetValue("Release")));
                    Console.WriteLine(".NET Framework Version 4.5 or later is not detected.");

        // Checking the version using >= will enable forward compatibility.
        private static string CheckFor45PlusVersion(int releaseKey)
            if (releaseKey >= 394802)
                return "4.6.2 or later";
            if (releaseKey >= 394254)
                return "4.6.1";
            if (releaseKey >= 393295)
                return "4.6";
            if ((releaseKey >= 379893))
                return "4.5.2";
            if ((releaseKey >= 378675))
                return "4.5.1";
            if ((releaseKey >= 378389))
                return "4.5";
            // This code should never execute. A non-null release key shoul
            // that 4.5 or later is installed.
            return "No 4.5 or later version detected";
    // Calling the GetDotNetVersion.Get45PlusFromRegistry method produces 
    // output like the following:
    //       .NET Framework Version: 4.6.1

How can I read a large text file line by line using Java?

You can use this code:


public class ReadTextFile {

    public static void main(String[] args) throws IOException {

        try {

            File f = new File("src/com/data.txt");

            BufferedReader b = new BufferedReader(new FileReader(f));

            String readLine = "";

            System.out.println("Reading file using Buffered Reader");

            while ((readLine = b.readLine()) != null) {

        } catch (IOException e) {



Replace specific text with a redacted version using Python

You can do it using named-entity recognition (NER). It's fairly simple and there are out-of-the-shelf tools out there to do it, such as spaCy.

NER is an NLP task where a neural network (or other method) is trained to detect certain entities, such as names, places, dates and organizations.


Sponge Bob went to South beach, he payed a ticket of $200!
I know, Michael is a good person, he goes to McDonalds, but donates to charity at St. Louis street.


NER with spacy

Just be aware that this is not 100%!

Here are a little snippet for you to try out:

import spacy

phrases = ['Sponge Bob went to South beach, he payed a ticket of $200!', 'I know, Michael is a good person, he goes to McDonalds, but donates to charity at St. Louis street.']
nlp = spacy.load('en')
for phrase in phrases:
   doc = nlp(phrase)
   replaced = ""
   for token in doc:
      if token in doc.ents:
         replaced+="XXXX "
         replaced+=token.text+" "

Read more here:

You could, instead of replacing with XXXX, replace based on the entity type, like:

if ent.label_ == "PERSON":
   replaced += "<PERSON> "


import re, random

personames = ["Jack", "Mike", "Bob", "Dylan"]

phrase = re.replace("<PERSON>", random.choice(personames), phrase)

JavaScript open in a new window, not tab

OK, after making a lot of test, here my concluson:

When you perform:'www.yourdomain.tld','_blank');'www.yourdomain.tld','myWindow');

or whatever you put in the destination field, this will change nothing: the new page will be opened in a new tab (so depend on user preference)

If you want the page to be opened in a new "real" window, you must put extra parameter. Like:'www.yourdomain.tld', 'mywindow','location=1,status=1,scrollbars=1, resizable=1, directories=1, toolbar=1, titlebar=1');

After testing, it seems the extra parameter you use, dont' really matter: this is not the fact you put "this parameter" or "this other one" which create the new "real window" but the fact there is new parameter(s).

But something is confused and may explain a lot of wrong answers:


 win1 ='myurl1', 'ID_WIN');
 win2 ='myurl2', 'ID_WIN', 'location=1,status=1,scrollbars=1');

And this:

 win2 ='myurl2', 'ID_WIN', 'location=1,status=1,scrollbars=1');
 win1 ='myurl1', 'ID_WIN');

will NOT give the same result.

In the first case, as you first open a page without extra parameter, it will open in a new tab. And in this case, the second call will be also opened in this tab because of the name you give.

In second case, as your first call is made with extra parameter, the page will be opened in a new "real window". And in that case, even if the second call is made without the extra parameter, it will also be opened in this new "real window"... but same tab!

This mean the first call is important as it decided where to put the page.

How to change the blue highlight color of a UITableViewCell?

1- Add a view to the content view of your cell.
2- Right click your cell.
3- Make the added view as "selectedBackgroundView" enter image description here

how to convert rgb color to int in java

You may declare a value in color.xml, and thus you can get integer value by calling the code below.

context.getColor(int resId);

How do I escape spaces in path for scp copy in Linux?

Sorry for using this Linux question to put this tip for Powershell on Windows 10: the space char escaping with backslashes or surrounding with quotes didn't work for me in this case. Not efficient, but I solved it using the "?" char instead:

for the file "tasks.txt Jun-22.bkp" I downloaded it using "tasks.txt?Jun-22.bkp"

what is the difference between XSD and WSDL

WSDL (Web Services Description Language) describes your service and its operations - what is the service called, which methods does it offer, what kind of in parameters and return values do these methods have?

It's a description of the behavior of the service - it's functionality.

XSD (Xml Schema Definition) describes the static structure of the complex data types being exchanged by those service methods. It describes the types, their fields, any restriction on those fields (like max length or a regex pattern) and so forth.

It's a description of datatypes and thus static properties of the service - it's about data.

Get values from other sheet using VBA

That will be (for you very specific example)




So get a F1 click and read about Worksheets collection, which contains Worksheet objects, which in turn has a Cells collection, holding Cell objects...

How to empty the content of a div

An alternative way to do it is:

var div = document.getElementById('myDiv');

However, using document.getElementById('myDiv').innerHTML = ""; is faster.

See: Benchmark test


Both methods preserve the div.

How to check if a Unix .tar.gz file is a valid file without uncompressing?

A nice option is to use tar -tvvf <filePath> which adds a line that reports the kind of file.

Example in a valid .tar file:

> tar -tvvf filename.tar 
drwxr-xr-x  0 diegoreymendez staff       0 Jul 31 12:46 ./testfolder2/
-rw-r--r--  0 diegoreymendez staff      82 Jul 31 12:46 ./testfolder2/._.DS_Store
-rw-r--r--  0 diegoreymendez staff    6148 Jul 31 12:46 ./testfolder2/.DS_Store
drwxr-xr-x  0 diegoreymendez staff       0 Jul 31 12:42 ./testfolder2/testfolder/
-rw-r--r--  0 diegoreymendez staff      82 Jul 31 12:42 ./testfolder2/testfolder/._.DS_Store
-rw-r--r--  0 diegoreymendez staff    6148 Jul 31 12:42 ./testfolder2/testfolder/.DS_Store
-rw-r--r--  0 diegoreymendez staff  325377 Jul  5 09:50 ./testfolder2/testfolder/Scala.pages
Archive Format: POSIX ustar format,  Compression: none

Corrupted .tar file:

> tar -tvvf corrupted.tar 
tar: Unrecognized archive format
Archive Format: (null),  Compression: none
tar: Error exit delayed from previous errors.

connecting MySQL server to NetBeans

I just had the same issue with Netbeans 8.2 and trying to connect to mySQL server on a Mac OS machine. The only thing that worked for me was to add the following to the url of the connection string: &serverTimezone=UTC (or if you are connecting via Hibernate.cfg.xml then escape the & as &) Not surprisingly I found the solution on this stack overflow post also:

MySQL JDBC Driver 5.1.33 - Time Zone Issue

Best Regards, Claudio

JavaScript DOM: Find Element Index In Container

You could make usage of Array.prototype.indexOf. For that, we need to somewhat "cast" the HTMLNodeCollection into a true Array. For instance:

var nodes = document.getElementById('list').children );

Then we could just call:

nodes.indexOf( liNodeReference );


var nodes = document.getElementById('list').children ),_x000D_
    liRef = document.getElementsByClassName('match')[0];_x000D_
console.log( nodes.indexOf( liRef ) );
<ul id="list">_x000D_
    <li class="match">bar</li>_x000D_
    <li>baz</li>    _x000D_

Failed to load resource: net::ERR_FILE_NOT_FOUND loading json.js

This error means that file was not found. Either path is wrong or file is not present where you want it to be. Try to access it by entering source address in your browser to check if it really is there. Browse the directories on server to ensure the path is correct. You may even copy and paste the relative path to be certain it is alright.

How to get Latitude and Longitude of the mobile device in android?

Above solutions is also correct, but some time if location is null then it crash the app or not working properly. The best way to get Latitude and Longitude of android is:

 Geocoder geocoder;
     String bestProvider;
     List<Address> user = null;
     double lat;
     double lng;

    LocationManager lm = (LocationManager) activity.getSystemService(Context.LOCATION_SERVICE);

     Criteria criteria = new Criteria();
     bestProvider = lm.getBestProvider(criteria, false);
     Location location = lm.getLastKnownLocation(bestProvider);

     if (location == null){
         Toast.makeText(activity,"Location Not found",Toast.LENGTH_LONG).show();
        geocoder = new Geocoder(activity);
        try {
            user = geocoder.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
        System.out.println(" DDD lat: " +lat+",  longitude: "+lng);

        }catch (Exception e) {

Detect if value is number in MySQL

Returns numeric rows

I found the solution with following query and works for me:

SELECT * FROM myTable WHERE col1 > 0;

This query return rows having only greater than zero number column that col1

Returns non numeric rows

if you want to check column not numeric try this one with the trick (!col1 > 0):

SELECT * FROM myTable WHERE !col1 > 0;

How to deal with page breaks when printing a large HTML table

Note: when using the page-break-after:always for the tag it will create a page break after the last bit of the table, creating an entirely blank page at the end every time! To fix this just change it to page-break-after:auto. It will break correctly and not create an extra blank page.

@media print
  table { page-break-after:auto }
  tr    { page-break-inside:avoid; page-break-after:auto }
  td    { page-break-inside:avoid; page-break-after:auto }
  thead { display:table-header-group }
  tfoot { display:table-footer-group }


Application Crashes With "Internal Error In The .NET Runtime"

Framework Version: v4.0.30319 Description: The process was terminated due to an unhandled exception. Exception Info: System.Reflection.TargetInvocationException

I have faced this Error, Application was working fine on some PCs and on some PCs giving the above error. I uninstall the Framework 4.5 and re-install this resolved my problem.


Laravel orderBy on a relationship

It is possible to extend the relation with query functions:

public function comments()
    return $this->hasMany('Comment')->orderBy('column');

[edit after comment]

class User
    public function comments()
        return $this->hasMany('Comment');

class Controller
    public function index()
        $column = Input::get('orderBy', 'defaultColumn');
        $comments = User::find(1)->comments()->orderBy($column)->get();

        // use $comments in the template

default User model + simple Controller example; when getting the list of comments, just apply the orderBy() based on Input::get(). (be sure to do some input-checking ;) )

jQuery autohide element after 5 seconds

$(function() {
    // setTimeout() function will be fired after page is loaded
    // it will wait for 5 sec. and then will fire
    // $("#successMessage").hide() function
    setTimeout(function() {
        $("#successMessage").hide('blind', {}, 500)
    }, 5000);

Note: In order to make you jQuery function work inside setTimeout you should wrap it inside

function() { ... }

AngularJS- Login and Authentication in each route and controller

The simplest manner of defining custom behavior for individual routes would be fairly easy:

1) routes.js: create a new property (like requireAuth) for any desired route

angular.module('yourApp').config(function($routeProvider) {
        .when('/home', {
            templateUrl: 'templates/home.html',
            requireAuth: true // our custom property
        .when('/login', {
            templateUrl: 'templates/login.html',
            redirectTo: '/home'

2) In a top-tier controller that isn't bound to an element inside the ng-view (to avoid conflict with angular $routeProvider), check if the newUrl has the requireAuth property and act accordingly

 angular.module('YourApp').controller('YourController', function ($scope, $location, session) {

     // intercept the route change event
     $scope.$on('$routeChangeStart', function (angularEvent, newUrl) {

         // check if the custom property exist
         if (newUrl.requireAuth && !session.user) {

             // user isn’t authenticated

How do I align spans or divs horizontally?

I would use:

.all {
display: table;
.maincontent {
float: left;
width: 60%; 
.sidebox { 
float: right;
width: 30%; 
<div class="all">
   <div class="maincontent">
   <div class="sidebox"> 

It's the first time I use this 'code tool' from overflow... but shoul do it by now...

How can I print the contents of an array horizontally?

Just loop through the array and write the items to the console using Write instead of WriteLine:

foreach(var item in array)
    Console.Write(item.ToString() + " ");

As long as your items don't have any line breaks, that will produce a single line.

...or, as Jon Skeet said, provide a little more context to your question.

How to check if Thread finished execution

For a thread you have the myThread.IsAlive property. It is false if the thread method returned or the thread was aborted.

Equivalent of typedef in C#

Both C++ and C# are missing easy ways to create a new type which is semantically identical to an exisiting type. I find such 'typedefs' totally essential for type-safe programming and its a real shame c# doesn't have them built-in. The difference between void f(string connectionID, string username) to void f(ConID connectionID, UserName username) is obvious ...

(You can achieve something similar in C++ with boost in BOOST_STRONG_TYPEDEF)

It may be tempting to use inheritance but that has some major limitations:

  • it will not work for primitive types
  • the derived type can still be casted to the original type, ie we can send it to a function receiving our original type, this defeats the whole purpose
  • we cannot derive from sealed classes (and ie many .NET classes are sealed)

The only way to achieve a similar thing in C# is by composing our type in a new class:

Class SomeType { 
  public void Method() { .. }

sealed Class SomeTypeTypeDef {
  public SomeTypeTypeDef(SomeType composed) { this.Composed = composed; }

  private SomeType Composed { get; }

  public override string ToString() => Composed.ToString();
  public override int GetHashCode() => HashCode.Combine(Composed);
  public override bool Equals(object obj) => obj is TDerived o && Composed.Equals(o.Composed); 
  public bool Equals(SomeTypeTypeDefo) => object.Equals(this, o);

  // proxy the methods we want
  public void Method() => Composed.Method();

While this will work it is very verbose for just a typedef. In addition we have a problem with serializing (ie to Json) as we want to serialize the class through its Composed property.

Below is a helper class that uses the "Curiously Recurring Template Pattern" to make this much simpler:

namespace Typedef {

  public abstract class Composer<TDerived, T> : IEquatable<TDerived> where TDerived : Composer<TDerived, T> {
    protected Composer(T composed) { this.Composed = composed; }
    protected Composer(TDerived d) { this.Composed = d.Composed; }

    protected T Composed { get; }

    public override string ToString() => Composed.ToString();
    public override int GetHashCode() => HashCode.Combine(Composed);
    public override bool Equals(object obj) => obj is Composer<TDerived, T> o && Composed.Equals(o.Composed); 
    public bool Equals(TDerived o) => object.Equals(this, o);

  class JsonCompositionConverter : JsonConverter {
    static FieldInfo GetCompositorField(Type t) {
      var fields = t.BaseType.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.FlattenHierarchy);
      if (fields.Length!=1) throw new JsonSerializationException();
      return fields[0];

    public override bool CanConvert(Type t) {
      var fields = t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.FlattenHierarchy);
      return fields.Length == 1;

    // assumes Compositor<T> has either a constructor accepting T or an empty constructor
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
      while (reader.TokenType == JsonToken.Comment && reader.Read()) { };
      if (reader.TokenType == JsonToken.Null) return null; 
      var compositorField = GetCompositorField(objectType);
      var compositorType = compositorField.FieldType;
      var compositorValue = serializer.Deserialize(reader, compositorType);
      var ctorT = objectType.GetConstructor(new Type[] { compositorType });
      if (!(ctorT is null)) return Activator.CreateInstance(objectType, compositorValue);
      var ctorEmpty = objectType.GetConstructor(new Type[] { });
      if (ctorEmpty is null) throw new JsonSerializationException();
      var res = Activator.CreateInstance(objectType);
      compositorField.SetValue(res, compositorValue);
      return res;

    public override void WriteJson(JsonWriter writer, object o, JsonSerializer serializer) {
      var compositorField = GetCompositorField(o.GetType());
      var value = compositorField.GetValue(o);
      serializer.Serialize(writer, value);


With Composer the above class becomes simply:

sealed Class SomeTypeTypeDef : Composer<SomeTypeTypeDef, SomeType> {
   public SomeTypeTypeDef(SomeType composed) : base(composed) {}

   // proxy the methods we want
   public void Method() => Composed.Method();

And in addition the SomeTypeTypeDef will serialize to Json in the same way that SomeType does.

Hope this helps !

PHP check whether property exists in object or class

To check if the property exists and if it's null too, you can use the function property_exists().


As opposed with isset(), property_exists() returns TRUE even if the property has the value NULL.

bool property_exists ( mixed $class , string $property )


if (property_exists($testObject, $property)) {
    //do something

Ubuntu, how do you remove all Python 3 but not 2

EDIT: As pointed out in recent comments, this solution may BREAK your system.

You most likely don't want to remove python3.

Please refer to the other answers for possible solutions.

Outdated answer (not recommended)

sudo apt-get remove 'python3.*'

Calculating average of an array list?

Why use a clumsy for loop with an index when you have the enhanced for loop?

private double calculateAverage(List <Integer> marks) {
  Integer sum = 0;
  if(!marks.isEmpty()) {
    for (Integer mark : marks) {
        sum += mark;
    return sum.doubleValue() / marks.size();
  return sum;

How can I get the current page's full URL on a Windows/IIS server?

Maybe, because you are under IIS,


is what you want, based on the URLs you used to explain.

For Apache, you'd use $_SERVER['REQUEST_URI'].

How to get the name of the current Windows user in JavaScript

JavaScript runs in the context of the current HTML document, so it won't be able to determine anything about a current user unless it's in the current page or you do AJAX calls to a server-side script to get more information.

JavaScript will not be able to determine your Windows user name.

How to remove specific element from an array using python

Your for loop is not right, if you need the index in the for loop use:

for index, item in enumerate(emails):
    # whatever (but you can't remove element while iterating)

In your case, Bogdan solution is ok, but your data structure choice is not so good. Having to maintain these two lists with data from one related to data from the other at same index is clumsy.

A list of tupple (email, otherdata) may be better, or a dict with email as key.

Error:Cannot fit requested classes in a single dex file.Try supplying a main-dex list. # methods: 72477 > 65536

What are dex files: Android app (APK) files contain executable bytecode files in the form of Dalvik Executable (DEX) files, which contain the compiled code used to run your app.

Reason for this exception: The DEX specification limits the total number of methods that can be referenced within a single DEX file to 65,536 (64K reference limit) —including Android framework methods, library methods, and methods in your own code.

Step 01. Add the following dependency as follows

For Non-Androidx Users,

dependencies {
  implementation ''
defaultConfig {
    minSdkVersion 16
    targetSdkVersion 28
    multiDexEnabled true  //ADD THIS LINE

For Androidx Users,

dependencies {
  implementation 'androidx.multidex:multidex:2.0.1'
    defaultConfig {
        minSdkVersion 16
        targetSdkVersion 28
        multiDexEnabled true  //ADD THIS LINE

Step 02:

After adding those Sync projects and before you run the project make sure to Build a project before the run. otherwise, you will get an exception.

get number of columns of a particular row in given excel using Java

Sometimes using row.getLastCellNum() gives you a higher value than what is actually filled in the file.
I used the method below to get the last column index that contains an actual value.

private int getLastFilledCellPosition(Row row) {
        int columnIndex = -1;

        for (int i = row.getLastCellNum() - 1; i >= 0; i--) {
            Cell cell = row.getCell(i);

            if (cell == null || CellType.BLANK.equals(cell.getCellType()) || StringUtils.isBlank(cell.getStringCellValue())) {
            } else {
                columnIndex = cell.getColumnIndex();

        return columnIndex;

php string to int

What do you even want the result to be? 888888? If so, just remove the spaces with str_replace, then convert.

Parsing json and searching through it

ObjectPath is a library that provides ability to query JSON and nested structures of dicts and lists. For example, you can search for all attributes called "foo" regardless how deep they are by using $

While the documentation focuses on the command line interface, you can perform the queries programmatically by using the package's Python internals. The example below assumes you've already loaded the data into Python data structures (dicts & lists). If you're starting with a JSON file or string you just need to use load or loads from the json module first.

import objectpath

data = [
    {'foo': 1, 'bar': 'a'},
    {'foo': 2, 'bar': 'b'},
    {'NoFooHere': 2, 'bar': 'c'},
    {'foo': 3, 'bar': 'd'},

tree_obj = objectpath.Tree(data)

# returns: (1, 2, 3)

Notice that it just skipped elements that lacked a "foo" attribute, such as the third item in the list. You can also do much more complex queries, which makes ObjectPath handy for deeply nested structures (e.g. finding where x has y that has z: $.x.y.z). I refer you to the documentation and tutorial for more information.

Named tuple and default values for optional keyword arguments

Since you are using namedtuple as a data class, you should be aware that python 3.7 will introduce a @dataclass decorator for this very purpose -- and of course it has default values.

An example from the docs:

class C:
    a: int       # 'a' has no default value
    b: int = 0   # assign a default value for 'b'

Much cleaner, readable and usable than hacking namedtuple. It is not hard to predict that usage of namedtuples will drop with the adoption of 3.7.

Mongoose (mongodb) batch insert?

Sharing working and relevant code from our project:

//documentsArray is the list of sampleCollection objects
    .then((res) => {
        console.log("insert sampleCollection result ", res);
    .catch(err => {
        console.log("bulk insert sampleCollection error ", err);

Are there any worse sorting algorithms than Bogosort (a.k.a Monkey Sort)?

There is a sort that's called bogobogosort. First, it checks the first 2 elements, and bogosorts them. Next it checks the first 3, bogosorts them, and so on.

Should the list be out of order at any time, it restarts by bogosorting the first 2 again. Regular bogosort has a average complexity of O(N!), this algorithm has a average complexity of O(N!1!2!3!...N!)

Edit: To give you an idea of how large this number is, for 20 elements, this algorithm takes an average of 3.930093*10^158 years,well above the proposed heat death of the universe(if it happens) of 10^100 years,

whereas merge sort takes around .0000004 seconds, bubble sort .0000016 seconds, and bogosort takes 308 years, 139 days, 19 hours, 35 minutes, 22.306 seconds, assuming a year is 365.242 days and a computer does 250,000,000 32 bit integer operations per second.

Edit2: This algorithm is not as slow as the "algorithm" miracle sort, which probably, like this sort, will get the computer sucked in the black hole before it successfully sorts 20 elemtnts, but if it did, I would estimate an average complexity of 2^(32(the number of bits in a 32 bit integer)*N)(the number of elements)*(a number <=10^40) years,

since gravity speeds up the chips alpha moving, and there are 2^N states, which is 2^640*10^40, or about 5.783*10^216.762162762 years, though if the list started out sorted, its complexity would only be O(N), faster than merge sort, which is only N log N even at the worst case.

Edit3: This algorithm is actually slower than miracle sort as the size gets very big, say 1000, since my algorithm would have a run time of 2.83*10^1175546 years, while the miracle sort algorithm would have a run time of 1.156*10^9657 years.

Single line sftp from terminal

SCP answer

The OP mentioned SCP, so here's that.

As others have pointed out, SFTP is a confusing since the upload syntax is completely different from the download syntax. It gets marginally easier to remember if you use the same form:


In reality, this is still a mess, and is why people still use "outdated" commands such as SCP:


SCP is secure but dated. It has some bugs that will never be fixed, namely crashing if the server's .bash_profile emits a message. However, in terms of usability, the devs were years ahead.

How to extract numbers from string in c?

Make a state machine that operates on one basic principle: is the current character a number.

  • When transitioning from non-digit to digit, you initialize your current_number := number.
  • when transitioning from digit to digit, you "shift" the new digit in:
    current_number := current_number * 10 + number;
  • when transitioning from digit to non-digit, you output the current_number
  • when from non-digit to non-digit, you do nothing.

Optimizations are possible.

jQuery if Element has an ID?

Simply use:

$(".parent a[id]");

PHP Date Format to Month Name and Year

I think your date data should look like 2013-08-14.

 $yrdata= strtotime('2013-08-14');
    echo date('M-Y', $yrdata);
// Output is Aug-2013

What is the difference between CMD and ENTRYPOINT in a Dockerfile?

In a nutshell:

  • CMD sets default command and/or parameters, which can be overwritten from command line when docker container runs.
  • ENTRYPOINT command and parameters will not be overwritten from command line. Instead, all command line arguments will be added after ENTRYPOINT parameters.

If you need more details or would like to see difference on example, there is a blog post that comprehensively compare CMD and ENTRYPOINT with lots of examples -

Round a double to 2 decimal places

Rounding a double is usually not what one wants. Instead, use String.format() to represent it in the desired format.

PHP - get base64 img string decode and save as jpg (resulting empty image )

Decode and save image as PNG

header('content-type: image/png');


        $ret = fopen($fullurl, 'r', true, $context);
        $contents = stream_get_contents($ret);
        $base64 = 'data:image/PNG;base64,' . base64_encode($contents);
        echo "<img src=$base64 />" ;


How can I control the width of a label tag?

You can definitely try this way

  display: inline-block;

Simple C example of doing an HTTP POST and consuming the response

A message has a header part and a message body separated by a blank line. The blank line is ALWAYS needed even if there is no message body. The header starts with a command and has additional lines of key value pairs separated by a colon and a space. If there is a message body, it can be anything you want it to be.

Lines in the header and the blank line at the end of the header must end with a carraige return and linefeed pair (see HTTP header line break style) so that's why those lines have \r\n at the end.

A URL has the form of http://host:port/path?query_string

There are two main ways of submitting a request to a website:

  • GET: The query string is optional but, if specified, must be reasonably short. Because of this the header could just be the GET command and nothing else. A sample message could be:

    GET /path?query_string HTTP/1.0\r\n
  • POST: What would normally be in the query string is in the body of the message instead. Because of this the header needs to include the Content-Type: and Content-Length: attributes as well as the POST command. A sample message could be:

    POST /path HTTP/1.0\r\n
    Content-Type: text/plain\r\n
    Content-Length: 12\r\n

So, to answer your question: if the URL you are interested in POSTing to is then there is no body or query string and, consequently, no reason to POST because there is nothing to put in the body of the message and so nothing to put in the Content-Type: and Content-Length:

I guess you could POST if you really wanted to. In that case your message would look like:

POST /apikey=ARG1&command=ARG2 HTTP/1.0\r\n

So to send the message the C program needs to:

  • create a socket
  • lookup the IP address
  • open the socket
  • send the request
  • wait for the response
  • close the socket

The send and receive calls won't necessarily send/receive ALL the data you give them - they will return the number of bytes actually sent/received. It is up to you to call them in a loop and send/receive the remainder of the message.

What I did not do in this sample is any sort of real error checking - when something fails I just exit the program. Let me know if it works for you:

#include <stdio.h> /* printf, sprintf */
#include <stdlib.h> /* exit */
#include <unistd.h> /* read, write, close */
#include <string.h> /* memcpy, memset */
#include <sys/socket.h> /* socket, connect */
#include <netinet/in.h> /* struct sockaddr_in, struct sockaddr */
#include <netdb.h> /* struct hostent, gethostbyname */

void error(const char *msg) { perror(msg); exit(0); }

int main(int argc,char *argv[])
    /* first what are we going to send and where are we going to send it? */
    int portno =        80;
    char *host =        "";
    char *message_fmt = "POST /apikey=%s&command=%s HTTP/1.0\r\n\r\n";

    struct hostent *server;
    struct sockaddr_in serv_addr;
    int sockfd, bytes, sent, received, total;
    char message[1024],response[4096];

    if (argc < 3) { puts("Parameters: <apikey> <command>"); exit(0); }

    /* fill in the parameters */

    /* create the socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) error("ERROR opening socket");

    /* lookup the ip address */
    server = gethostbyname(host);
    if (server == NULL) error("ERROR, no such host");

    /* fill in the structure */
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(portno);

    /* connect the socket */
    if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
        error("ERROR connecting");

    /* send the request */
    total = strlen(message);
    sent = 0;
    do {
        bytes = write(sockfd,message+sent,total-sent);
        if (bytes < 0)
            error("ERROR writing message to socket");
        if (bytes == 0)
    } while (sent < total);

    /* receive the response */
    total = sizeof(response)-1;
    received = 0;
    do {
        bytes = read(sockfd,response+received,total-received);
        if (bytes < 0)
            error("ERROR reading response from socket");
        if (bytes == 0)
    } while (received < total);

    if (received == total)
        error("ERROR storing complete response from socket");

    /* close the socket */

    /* process response */

    return 0;

Like the other answer pointed out, 4096 bytes is not a very big response. I picked that number at random assuming that the response to your request would be short. If it can be big you have two choices:

  • read the Content-Length: header from the response and then dynamically allocate enough memory to hold the whole response.
  • write the response to a file as the pieces arrive

Additional information to answer the question asked in the comments:

What if you want to POST data in the body of the message? Then you do need to include the Content-Type: and Content-Length: headers. The Content-Length: is the actual length of everything after the blank line that separates the header from the body.

Here is a sample that takes the following command line arguments:

  • host
  • port
  • command (GET or POST)
  • path (not including the query data)
  • query data (put into the query string for GET and into the body for POST)
  • list of headers (Content-Length: is automatic if using POST)

So, for the original question you would run:

a.out 80 GET "/apikey=ARG1&command=ARG2"

And for the question asked in the comments you would run:

a.out 80 POST / "name=ARG1&value=ARG2" "Content-Type: application/x-www-form-urlencoded"

Here is the code:

#include <stdio.h> /* printf, sprintf */
#include <stdlib.h> /* exit, atoi, malloc, free */
#include <unistd.h> /* read, write, close */
#include <string.h> /* memcpy, memset */
#include <sys/socket.h> /* socket, connect */
#include <netinet/in.h> /* struct sockaddr_in, struct sockaddr */
#include <netdb.h> /* struct hostent, gethostbyname */

void error(const char *msg) { perror(msg); exit(0); }

int main(int argc,char *argv[])
    int i;

    /* first where are we going to send it? */
    int portno = atoi(argv[2])>0?atoi(argv[2]):80;
    char *host = strlen(argv[1])>0?argv[1]:"localhost";

    struct hostent *server;
    struct sockaddr_in serv_addr;
    int sockfd, bytes, sent, received, total, message_size;
    char *message, response[4096];

    if (argc < 5) { puts("Parameters: <host> <port> <method> <path> [<data> [<headers>]]"); exit(0); }

    /* How big is the message? */
        message_size+=strlen("%s %s%s%s HTTP/1.0\r\n");        /* method         */
        message_size+=strlen(argv[3]);                         /* path           */
        message_size+=strlen(argv[4]);                         /* headers        */
            message_size+=strlen(argv[5]);                     /* query string   */
        for(i=6;i<argc;i++)                                    /* headers        */
        message_size+=strlen("\r\n");                          /* blank line     */
        message_size+=strlen("%s %s HTTP/1.0\r\n");
        message_size+=strlen(argv[3]);                         /* method         */
        message_size+=strlen(argv[4]);                         /* path           */
        for(i=6;i<argc;i++)                                    /* headers        */
            message_size+=strlen("Content-Length: %d\r\n")+10; /* content length */
        message_size+=strlen("\r\n");                          /* blank line     */
            message_size+=strlen(argv[5]);                     /* body           */

    /* allocate space for the message */

    /* fill in the parameters */
            sprintf(message,"%s %s%s%s HTTP/1.0\r\n",
                strlen(argv[3])>0?argv[3]:"GET",               /* method         */
                strlen(argv[4])>0?argv[4]:"/",                 /* path           */
                strlen(argv[5])>0?"?":"",                      /* ?              */
                strlen(argv[5])>0?argv[5]:"");                 /* query string   */
            sprintf(message,"%s %s HTTP/1.0\r\n",
                strlen(argv[3])>0?argv[3]:"GET",               /* method         */
                strlen(argv[4])>0?argv[4]:"/");                /* path           */
        for(i=6;i<argc;i++)                                    /* headers        */
        strcat(message,"\r\n");                                /* blank line     */
        sprintf(message,"%s %s HTTP/1.0\r\n",
            strlen(argv[3])>0?argv[3]:"POST",                  /* method         */
            strlen(argv[4])>0?argv[4]:"/");                    /* path           */
        for(i=6;i<argc;i++)                                    /* headers        */
            sprintf(message+strlen(message),"Content-Length: %d\r\n",strlen(argv[5]));
        strcat(message,"\r\n");                                /* blank line     */
            strcat(message,argv[5]);                           /* body           */

    /* What are we going to send? */

    /* create the socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) error("ERROR opening socket");

    /* lookup the ip address */
    server = gethostbyname(host);
    if (server == NULL) error("ERROR, no such host");

    /* fill in the structure */
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(portno);

    /* connect the socket */
    if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
        error("ERROR connecting");

    /* send the request */
    total = strlen(message);
    sent = 0;
    do {
        bytes = write(sockfd,message+sent,total-sent);
        if (bytes < 0)
            error("ERROR writing message to socket");
        if (bytes == 0)
    } while (sent < total);

    /* receive the response */
    total = sizeof(response)-1;
    received = 0;
    do {
        bytes = read(sockfd,response+received,total-received);
        if (bytes < 0)
            error("ERROR reading response from socket");
        if (bytes == 0)
    } while (received < total);

    if (received == total)
        error("ERROR storing complete response from socket");

    /* close the socket */

    /* process response */

    return 0;

PDO error message?

Maybe this post is too old but it may help as a suggestion for someone looking around on this : Instead of using:


Use PHP implode() function:

 echo 'Error occurred:'.implode(":",$this->pdo->errorInfo());

This should print the error code, detailed error information etc. that you would usually get if you were using some SQL User interface.

Hope it helps

SQL Server Restore Error - Access is Denied

lost a couple of hours to this problem too. got it going though:

"access denied" in my case really did mean "access denied". mssqlstudio's user account on my windows device did NOT have full control of the folder specified in the error message. i gave it full control. access was no longer denied and the restore succeeded.

why was the folder locked up for studio ? who knows ? i got enough questions to deal with as it is without trying to answer more.

Flutter plugin not installed error;. When running flutter doctor

When you execute the flutter doctor command it checks your environment and displays a report to the terminal window. In your case it seems that you did not install the dart and flutter plugin to be able to use them in Android Studio.

To install a plugin, click on Files>Settings>Plugins>install jetbrain plugins

The plugins will add new functionalities to android studio related to flutter. Example it will add the flutter inspector, outliner.

The SDK that you added to the path, will be needed when creating a new flutter project.

enter image description here

PHP: How to generate a random, unique, alphanumeric string for use in a secret link?

we can use this two line of code to generate unique string have tested around 10000000 times of iteration

  $sffledStr= str_shuffle('abscdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!@#$%^&*()_-+');
    $uniqueString = md5(time().$sffledStr);

'ssh-keygen' is not recognized as an internal or external command

I found an easy solution to fix this :

In the command prompt, go to your git\bin directory, and then execute your commands from here

Angular EXCEPTION: No provider for Http

Import the HttpModule

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

    imports: [ BrowserModule, HttpModule ],
    providers: [],
    declarations: [ AppComponent ],
    bootstrap: [ AppComponent ]
export default class AppModule { }


Ideally, you split up this code in two separate files. For further information read:

Calling a java method from c++ in Android

Solution posted by Denys S. in the question post:

I quite messed it up with c to c++ conversion (basically env variable stuff), but I got it working with the following code for C++:

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

jstring Java_the_package_MainActivity_getJniString( JNIEnv* env, jobject obj){

    jstring jstr = (*env)->NewStringUTF(env, "This comes from jni.");
    jclass clazz = (*env)->FindClass(env, "com/inceptix/android/t3d/MainActivity");
    jmethodID messageMe = (*env)->GetMethodID(env, clazz, "messageMe", "(Ljava/lang/String;)Ljava/lang/String;");
    jobject result = (*env)->CallObjectMethod(env, obj, messageMe, jstr);

    const char* str = (*env)->GetStringUTFChars(env,(jstring) result, NULL); // should be released but what a heck, it's a tutorial :)
    printf("%s\n", str);

    return (*env)->NewStringUTF(env, str);

And next code for java methods:

    public class MainActivity extends Activity {
    private static String LIB_NAME = "thelib";

    static {

    /** Called when the activity is first created. */
    public void onCreate(Bundle savedInstanceState) {
        TextView tv = (TextView) findViewById(;

    // please, let me live even though I used this dark programming technique
    public String messageMe(String text) {
        return text;

    public native String getJniString();

git status shows modifications, git checkout -- <file> doesn't remove them

I was only able to fix this by temporary deleting my repo's .gitattributes file (which defined * text=auto and *.c text).

I ran git status after deleting and the modifications were gone. They didn't return even after .gitattributes was put back in place.

How do I reference a local image in React?

put your images in the public folder or make a subfolder in your public folder and put your images there. for example:

  1. you put "completative-reptile.jpg" in the public folder, then you can access it as
  1. you put completative-reptile.jpg at public/static/images, then you can access it as

#1071 - Specified key was too long; max key length is 767 bytes

What character encoding are you using? Some character sets (like UTF-16, et cetera) use more than one byte per character.

What do the return values of Comparable.compareTo mean in Java?

Official Definition

From the reference docs of Comparable.compareTo(T):

Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y. (This implies that x.compareTo(y) must throw an exception iff y.compareTo(x) throws an exception.)

The implementor must also ensure that the relation is transitive: (x.compareTo(y)>0 && y.compareTo(z)>0) implies x.compareTo(z)>0.

Finally, the implementor must ensure that x.compareTo(y)==0 implies that sgn(x.compareTo(z)) == sgn(y.compareTo(z)), for all z.

It is strongly recommended, but not strictly required that (x.compareTo(y)==0) == (x.equals(y)). Generally speaking, any class that implements the Comparable interface and violates this condition should clearly indicate this fact. The recommended language is "Note: this class has a natural ordering that is inconsistent with equals."

In the foregoing description, the notation sgn(expression) designates the mathematical signum function, which is defined to return one of -1, 0, or 1 according to whether the value of expression is negative, zero or positive.

My Version

In short:



  • a negative int if this < that
  • 0 if this == that
  • a positive int if this > that

where the implementation of this method determines the actual semantics of < > and == (I don't mean == in the sense of java's object identity operator)



will yield something smaller than 0 as abc is alphabetically before def.


will yield something larger than 0 because 2 is larger than 1.

Some additional points

Note: It is good practice for a class that implements Comparable to declare the semantics of it's compareTo() method in the javadocs.

Note: you should read at least one of the following:

Warning: you should never rely on the return values of compareTo being -1, 0 and 1. You should always test for x < 0, x == 0, x > 0, respectively.