Try:

    gcc -dumpspecs | grep pthread

and look for anything that starts with `%{pthread:`.

On my computer, this causes files to be compiled with `-D_REENTRANT`, and linked with `-lpthread`. On other platforms, this could differ. Use `-pthread` for most portability.

Using `_REENTRANT`, on GNU libc, changes the way some libc headers work. As a specific example, it makes `errno` call a function returning a thread-local location.

From `man gcc`:

&gt; -pthread
&gt;            Adds support for multithreading with the pthreads
&gt; library.  This
&gt;            option sets flags for both the preprocessor and linker.




I have the following JSON returned in a variable called data.

**THIS IS THE JSON THAT GETS RETURNED...**

    [ 
    {&quot;Id&quot;: 10004, &quot;PageName&quot;: &quot;club&quot;}, 
    {&quot;Id&quot;: 10040, &quot;PageName&quot;: &quot;qaz&quot;}, 
    {&quot;Id&quot;: 10059, &quot;PageName&quot;: &quot;jjjjjjj&quot;}
    ]

and I am trying to loop through the collection using $.each but I am running into problems where the alert is showing undefined. I have tried a lot of different syntax but can&#39;t seem to figure this out.

The JQuery I am using is

	$.each(data, function(i, item) {
		alert(item.PageName);
	});

Can any one point me in the right direction?

**EDIT**
This is the code I am using to grab the data

    $.getJSON(&#39;/Cms/GetPages/123&#39;, null, function(data) {
      fillSelect(data);
    });

and this is the function that gets called upon call back

    function fillSelect(data) {
      alert(data);
      $.each(data, function(i, item) {
        alert(item.PageName);
      });
    }


**EDIT 2**
This is slightly confusing me, according to the docs it should work as I have it, but it doesn&#39;t. According to fiddler the header shows:-

    Content-Type: application/json; charset=utf-8

and the JSON is exactly correct above. I am using chrome if this makes any different. Will test in IE and FF....

**EDIT 3**

using $.get produces

    &quot;[\r\n {\r\n \&quot;Id\&quot;: 10041,\r\n \&quot;PageName\&quot;: \&quot;01234567890\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 2\r\n },\r\n {\r\n \&quot;Id\&quot;: 10001,\r\n \&quot;PageName\&quot;: \&quot;about\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 1\r\n },\r\n {\r\n \&quot;Id\&quot;: 10056,\r\n \&quot;PageName\&quot;: \&quot;fdgdfgdfg\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 1\r\n },\r\n {\r\n \&quot;Id\&quot;: 10052,\r\n \&quot;PageName\&quot;: \&quot;hjkhjk\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 2\r\n },\r\n {\r\n \&quot;Id\&quot;: 10059,\r\n \&quot;PageName\&quot;: \&quot;jjjjjjj\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 1\r\n },\r\n {\r\n \&quot;Id\&quot;: 10057,\r\n \&quot;PageName\&quot;: \&quot;qqqqq\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 2\r\n },\r\n {\r\n \&quot;Id\&quot;: 10054,\r\n \&quot;PageName\&quot;: \&quot;qwqw\&quot;,\r\n \&quot;MetaId\&quot;: 1000,\r\n \&quot;TemplateId\&quot;: 2\r\n }\r\n]&quot;

jquery loop on Json data using $.each

How to load a different colorscheme when doing `vimdiff`. 

I want this because the my current colorscheme does not show some diffs properly in `vimdiff`, For. eg some diff is shown with same fg/bg color. This makes it very hard to understand the diff. So every time i do a `vimdiff` i have to do `:colorscheme some_other_scheme`

Can this be done in `.vimrc` file?

Load different colorscheme when using vimdiff

In various multi threaded C and C++ projects I&#39;ve seen the `-pthread` flag applied to both the compiling and linking stage while others don&#39;t use it at all and just pass `-lpthread` to the linking stage.

Is there any danger not compiling and linking with the `-pthread` flag - i.e. what does `-pthread` actually do ? I&#39;m primarily interested in Linux platforms.

Significance of -pthread flag when compiling

<p>In various multi threaded C and C++ projects I've seen the <code>-pthread</code> flag applied to both the compiling and linking stage while others don't use it at all and just pass <code>-lpthread</code> to the linking stage.</p>
<p>Is there any danger not compiling and linking with the <code>-pthread</code> flag - i.e. what does <code>-pthread</code> actually do ? I'm primarily interested in Linux platforms.</p>


I have two classes declared as below:

    class User
    {
    public:
      MyMessageBox dataMsgBox;
    };
    
    class MyMessageBox
    {
    public:
      void sendMessage(Message *msg, User *recvr);
      Message receiveMessage();
      vector&lt;Message&gt; *dataMessageList;
    };

When I try to compile it using gcc, it gives the following error:

&gt;MyMessageBox does not name a type

&quot;X does not name a type&quot; error in C++

I have a video file recorded from the front of a moving vehicle. I am going to use OpenCV for object detection and recognition but I&#39;m stuck on one aspect. How can I determine the distance from a recognized object. 

I can know my current speed and real-world GPS position but that is all. I can&#39;t make any assumptions about the object I&#39;m tracking. I am planning to use this to track and follow objects without colliding with them. Ideally I would like to use this data to derive the object&#39;s real-world position, which I could do if I could determine the distance from the camera to the object.

How can I determine distance from an object in a video?

So I found out that C(++) programs actually don&#39;t compile to plain &quot;binary&quot; (I may have gotten some things wrong here, in that case I&#39;m sorry :D) but to a range of things (symbol table, os-related stuff,...) but...

- Does assembler &quot;compile&quot; to pure binary? That means no extra stuff besides resources like predefined strings, etc.

- If C compiles to something else than plain binary, how can that small assembler bootloader just copy the instructions from the HDD to memory and execute them? I mean if the OS kernel, which is probably written in C, compiles to something different than plain binary - how does the bootloader handle it?

edit: I know that assembler doesn&#39;t &quot;compile&quot; because it only has your machine&#39;s instruction set - I didn&#39;t find a good word for what assembler &quot;assembles&quot; to. If you have one, leave it here as comment and I&#39;ll change it.

What do C and Assembler actually compile to?

I was looking at some example C++ code for a hardware interface I&#39;m working with and noticed a lot of statements along the following lines:

    if ( NULL == pMsg ) return rv;

I&#39;m sure I&#39;ve heard people say that putting the constant first is a good idea, but why is that? Is it just so that if you have a large statement you can quickly see what you&#39;re comparing against or is there more to it?





What&#39;s the reasoning behind putting constants in &#39;if&#39; statements first?

I am new to C++ programming, but I have experience in Java. I need guidance on how to pass objects to functions in C++.

Do I need to pass pointers, references, or non-pointer and non-reference values? I remember in Java there are no such issues since we pass just the variable that holds reference to the objects.

It would be great if you could also explain where to use each of those options.

How to pass objects to functions in C++?

I am using a GNU-make Makefile to build a C project with several targets (`all`, `clean`, and a few project specific targets). In the process of debugging, I would like to append some flags to a single build without permanently editing the Makefile (e.g. add debugging symbols or set a preprocessor flag).

In the past, I have done that as follows (using the debugging symbols example):

    make target CFLAGS+=-g

Unfortunately, this is not appending to the `CFLAGS` variable, but instead, clearing it and stopping it from compiling. Is there a clean way of doing this without defining some sort of dummy variable appended to the end of `CFLAGS` and `LDFLAGS`?

Append to GNU make variables via command line

What does `malloc(0)` return?

Would the answer be same for `realloc(malloc(0),0)`?

    #include&lt;stdio.h&gt;
    #include&lt;malloc.h&gt;
    int main()
    {
            printf(&quot;%p\n&quot;, malloc(0));
            printf(&quot;%p\n&quot;, realloc(malloc(0), 0));
            return 0;
    }

Output from Linux GCC:

    manav@manav-workstation:~$ gcc -Wall mal.c
    manav@manav-workstation:~$ ./a.out
    0x9363008
    (nil)
    manav@manav-workstation:~$

The output keep changing everytime for `malloc(0)`. Is this a standard answer? And why would anyone be interested in getting such a pointer, other than academic research?

**EDIT:**

If `malloc(0)` returns dummy pointer, then how does following works:

    int main()
    {
        void *ptr = malloc(0);
        printf(&quot;%p\n&quot;, realloc(ptr, 1024));
        return 0;
    }

**EDIT:**

The following code outputs &quot;possible&quot; for every iteration. Why should it not fail ?

    #include&lt;stdio.h&gt;
    #include&lt;malloc.h&gt;
    int main()
    {
    
            int i;
            void *ptr;
            printf(&quot;Testing using BRUTE FORCE\n&quot;);
            for (i=0; i&lt;65000; i++)
            {
                    ptr = malloc(0);
                    if (ptr == realloc(ptr, 1024))
                            printf(&quot;Iteration %d: possible\n&quot;, i);
                    else
                    {
                            printf(&quot;Failed for iteration %d\n&quot;, i);
                            break;
                    }
            }
            return 0;
    }



What does malloc(0) return?

How can I print a non-null-terminated string using printf, assuming that I know the length of the string at runtime?

How do I print a non-null-terminated string using printf?

I&#39;m having trouble distinguishing the practical difference between calling `glFlush()` and `glFinish()`.

The docs say that `glFlush()` and `glFinish()` will push all buffered operations to OpenGL so that one can be assured they will all be executed, the difference being that `glFlush()` returns immediately where as `glFinish()` blocks until all the operations are complete.

Having read the definitions, I figured that if I were to use `glFlush()` that I would probably run into the problem of submitting more operations to OpenGL than it could execute. So, just to try, I swapped out my `glFinish()` for a `glFlush()` and lo and behold, my program ran (as far as I could tell), the exact same; frame rates, resource usage, everything was the same.

So I&#39;m wondering if there&#39;s much difference between the two calls, or if my code makes them run no different. Or where one should be used vs. the other.
I also figured that OpenGL would have some call like `glIsDone()` to check whether or not all the buffered commands for a `glFlush()` are complete or not (so one doesn&#39;t send operations to OpenGL faster than they can be executed), but I could find no such function.

My code is the typical game loop:

    while (running) {
        process_stuff();
        render_stuff();
    }

opengl: glFlush() vs. glFinish()

Is it possible to &#39;hibernate&#39; a process in linux?
Just like &#39;hibernate&#39; in laptop, I would to write all the memory used by a process to disk, free up the RAM. And then later on, I can &#39;resume the process&#39;, i.e, reading all the data from memory and put it back to RAM and I can continue with my process?


How to &quot;hibernate&quot; a process in Linux by storing its memory to disk and restoring it later?

At the moment I have to go to `/usr/java/apache-solr-1.4.0/example` and then do:

    java -jar start.jar

How do I get this to start automatically on boot? 

I&#39;m on a shared Linux server.


How to start Solr automatically?

I need to have the ability to create user accounts on my Linux (Fedora 10) and automatically assign a password via a bash script(or otherwise, if need be).

It&#39;s easy to create the user via Bash e.g.:

    [whoever@server ]#  /usr/sbin/useradd newuser

Is it possible to assign a password in Bash, something functionally similar to this, but automatically:

    [whoever@server ]# passwd newuser
    Changing password for user testpass.
    New UNIX password:
    Retype new UNIX password: 
    passwd: all authentication tokens updated successfully.
    [whoever@server ]#


How to automatically add user account AND password with a Bash script?

Does anybody know an ISO image of a up-to-date Linux distribution aimed at web developers with one, some or all of the following features:

   * LAMP stack readily set up (Readily installed Apache 2, virtual sites directory structure (hosting), PHP installed, mySQL installed)

   * Ruby/RoR set up for a beginner to start with
   
   * Subversion set up for multiple repositories

   * Firewall configured for functioning as a web server (Port 80 open, not much else)
 
   * Python and Trac installed and integrated with Apache (Multi-environment capable) 

Background:

I have a powerful new workstation and would like to set up a number of virtual machines for testing, development and version control, preferably on Linux. The machines will not be exposed to the public.

I would like to save as much installation and set up work as possible - setting up everything from the above list would cost me weeks if I&#39;d do it alone.

&gt; **Bounty**
&gt;
&gt; I have had to put this on the shelf for the time being due to other, more pressing projects. The suggestions made are already a brilliant list; I&#39;m putting a bounty on the question to try and gather as much input as possible, so this can be the reference question on the issue for future generations.
&gt;
&gt; I will be awarding the bounty either based on popular vote or on a whim, from what looks the best solution to me.

&lt;!-- Note for statistical purposes: This question had 494 views at the start of the bounty. --&gt;

Pre-installed Linux for Web Developers?

If I try to compile a program with

    #include &lt;pthread.h&gt;
in it, I get the error:

    pthread.h: No such file or directory

Is it possible to get this to compile in a Windows environment?

I am using Vista with the latest MinGW.

I do not want to use the Microsoft Windows Services for UNIX Version 3.5 as I will have to move this to a Unix environment.

Can I get Unix&#39;s pthread.h to compile in Windows?

In my destructor I want to destroy a thread cleanly.

My goal is to wait for a thread to finish executing and THEN destroy the thread.

The only thing I found about querying the state of a pthread is [pthread_attr_setdetachstate][1] but this only tells you if your thread is:

 - PTHREAD_CREATE_DETACHED 
 - PTHREAD_CREATE_JOINABLE

Both of those have nothing to do with whether the thread is still running or not.

**How do you query a pthread to see if it is still running?**

  [1]: https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getdetachstate.txt

How do you query a pthread to see if it is still running?

I&#39;am new to C and would like to play with threads a bit. I would like to return some value from a thread using `pthread_exit()`

My code is as follows:

    #include &lt;pthread.h&gt;
    #include &lt;stdio.h&gt;
    
    void *myThread()
    {
       int ret = 42;
       pthread_exit(&amp;ret);
    }
    
    int main()
    {
       pthread_t tid;
       void *status;
     
       pthread_create(&amp;tid, NULL, myThread, NULL);
       pthread_join(tid, &amp;status);
    
       printf(&quot;%d\n&quot;,*(int*)status);   
     
       return 0;
    }

I would expect the program output `&quot;42\n&quot;` but it outputs a random number. How can I print the returned value?

It seems to be a problem that I am returning a pointer to a local variable. What is the best practice of returning/storing variables of multiple threads? A global hash table?

How to return a value from pthread threads in C?

Is there any way of setting the name of a thread in Linux?

My main purpose is it would be helpful while debugging, and also nice if that name was exposed through e.g. `/proc/$PID/task/$TID/...`


How to set the name of a thread in Linux pthreads?

I&#39;ve been trying to understand the intricacies of how POSIX threads and POSIX signals interact. In particular, I&#39;m interested in:

* What&#39;s the best way to control which thread a signal is delivered to (assuming it isn&#39;t fatal in the first place)?
* What is the best way to tell another thread (that might actually be busy) that the signal has arrived? (I already know that it&#39;s a bad idea to be using pthread condition variables from a signal handler.)
* How can I safely handle passing the information that a signal has occurred to other threads? Does this need to happen in the signal handler? (I do not in general want to kill the other threads; I need a far subtler approach.)

For reference about why I want this, I&#39;m researching how to convert the [TclX](http://sourceforge.net/projects/tclx/) package to support threads, or to split it up and at least make some useful parts support threads. Signals are one of those parts that is of particular interest.

Content Type	Original Author	Original Content on Stackoverflow
Question	leeeroy	View Question on Stackoverflow
Solution 1 - C++	Chris Jester-Young	View Answer on Stackoverflow
Solution 2 - C++	Dmitry	View Answer on Stackoverflow

Significance of -pthread flag when compiling

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Load different colorscheme when using vimdiff

jquery loop on Json data using $.each

Attributions