To get a list of all the predefined macros that the compiler uses, use this:

    clang -dM -E -x c /dev/null

You can do the same for gcc.


Found the answer using `strings` + `grep` :

    $ strings /usr/bin/clang | grep __ | grep -i clang
    __clang__


This question has been answered for years but let me add (for future reference) how it is done in **Windows**:
    
    echo | clang -dM -E -

same as for GCC:

    echo | gcc -dM -E -

Please note: The last dash `-` is actually important! (Otherwise you get `error: no input files` for both compilers)

I don&#39;t really understand how modulus division works.
I was calculating `27 % 16` and wound up with `11` and I don&#39;t understand why.

I can&#39;t seem to find an explanation in layman&#39;s terms online.
Can someone elaborate on a very high level as to what&#39;s going on here?

How Does Modulus Divison Work

Consider I have an anchor which looks like this

     &lt;div class=&quot;res&quot;&gt;
         &lt;a href=&quot;~/Resumes/Resumes1271354404687.docx&quot;&gt;
             ~/Resumes/Resumes1271354404687.docx
         &lt;/a&gt;
     &lt;/div&gt;

**NOTE:** There won&#39;t be any id or class for the anchor...

I want to get either href/text in the jQuery `onclick` of that anchor.


How to get anchor text/href on click using jQuery?

I&#39;m trying to detect the compiler used to compile my source code. I can easily find predefined macros to check for MSVC or GCC (see http://predef.sourceforge.net/ for example), but I cannot find any macro to check for clang.

Does someone know if clang defines a macro like `__CLANG__` in order to know what is currently compiling my code ?

What predefined macro can I use to detect clang?

<p>I'm trying to detect the compiler used to compile my source code. I can easily find predefined macros to check for MSVC or GCC (see <a href="http://predef.sourceforge.net/" target="_blank" rel="noopener noreferrer">http://predef.sourceforge.net/</a> for example), but I cannot find any macro to check for clang.</p>
<p>Does someone know if clang defines a macro like <code>__CLANG__</code> in order to know what is currently compiling my code ?</p>


&gt; **Possible Duplicates:**  
&gt; [What makes more sense - char* string or char *string?](https://stackoverflow.com/questions/558474/what-makes-more-sense-char-string-or-char-string)
[Pointer declarations in C++: placement of the asterisk](https://stackoverflow.com/questions/180401/pointer-declarations-in-c-placement-of-the-asterisk)  
&lt;!-- End of automatically inserted text --&gt;

I&#39;ve seen mixed versions of this in a lot of code. (This applies to C and C++, by the way.) People seem to declare pointers in one of two ways, and I have no idea which one is correct, of if it even matters.

The first way it to put the asterisk adjacent the type name, like so:

    someType* somePtr;

The second way is to put the asterisk adjacent the name of the variable, like so:

    someType *somePtr;

This has been driving me nuts for some time now. Is there any standard way of declaring pointers? Does it even matter how pointers are declared? I&#39;ve used both declarations before, and I know that the compiler doesn&#39;t care which way it is. However, the fact that I&#39;ve seen pointers declared in two different ways leads me to believe that there&#39;s a reason behind it. I&#39;m curious if either method is more readable or logical in some way that I&#39;m missing.

Declaring pointers; asterisk on the left or right of the space between the type and name?

How can I convert a mixed case string to a lowercase string in C?

How do I lowercase a string in C?

I want to write a signal handler to catch SIGSEGV. 
I protect a block of memory for read or write using

    char *buffer;
    char *p;
    char a;
    int pagesize = 4096;
    
    mprotect(buffer,pagesize,PROT_NONE)

This protects pagesize bytes of memory starting at buffer against any reads or writes.

Second, I try to read the memory:

    p = buffer;
    a = *p 

This will generate a SIGSEGV, and my handler will be called. 
So far so good. My problem is that, once the handler is called, I want to change the access write of the memory by doing 

    mprotect(buffer,pagesize,PROT_READ);

and continue normal functioning of my code. I do not want to exit the function.
On future writes to the same memory, I want to catch the signal again and modify the write rights and then record that event.

Here is [the code][1]:

    #include &lt;signal.h&gt;
    #include &lt;stdio.h&gt;
    #include &lt;malloc.h&gt;
    #include &lt;stdlib.h&gt;
    #include &lt;errno.h&gt;
    #include &lt;sys/mman.h&gt;
    
    #define handle_error(msg) \
    	do { perror(msg); exit(EXIT_FAILURE); } while (0)
    
    char *buffer;
    int flag=0;
    
    static void handler(int sig, siginfo_t *si, void *unused)
    {
    	printf(&quot;Got SIGSEGV at address: 0x%lx\n&quot;,(long) si-&gt;si_addr);
    	printf(&quot;Implements the handler only\n&quot;);
    	flag=1;
    	//exit(EXIT_FAILURE);
    }
    
    int main(int argc, char *argv[])
    {
    	char *p; char a;
    	int pagesize;
    	struct sigaction sa;
    
    	sa.sa_flags = SA_SIGINFO;
    	sigemptyset(&amp;sa.sa_mask);
    	sa.sa_sigaction = handler;
    	if (sigaction(SIGSEGV, &amp;sa, NULL) == -1)
    		handle_error(&quot;sigaction&quot;);
    
    	pagesize=4096;
    
    	/* Allocate a buffer aligned on a page boundary;
    	   initial protection is PROT_READ | PROT_WRITE */
    
    	buffer = memalign(pagesize, 4 * pagesize);
    	if (buffer == NULL)
    		handle_error(&quot;memalign&quot;);
    
    	printf(&quot;Start of region:        0x%lx\n&quot;, (long) buffer);
    	printf(&quot;Start of region:        0x%lx\n&quot;, (long) buffer+pagesize);
    	printf(&quot;Start of region:        0x%lx\n&quot;, (long) buffer+2*pagesize);
    	printf(&quot;Start of region:        0x%lx\n&quot;, (long) buffer+3*pagesize);
    	//if (mprotect(buffer + pagesize * 0, pagesize,PROT_NONE) == -1)
    	if (mprotect(buffer + pagesize * 0, pagesize,PROT_NONE) == -1)
    		handle_error(&quot;mprotect&quot;);
    
    	//for (p = buffer ; ; )
    	if(flag==0)
    	{
    		p = buffer+pagesize/2;
    		printf(&quot;It comes here before reading memory\n&quot;);
    		a = *p; //trying to read the memory
    		printf(&quot;It comes here after reading memory\n&quot;);
    	}
    	else
    	{
    		if (mprotect(buffer + pagesize * 0, pagesize,PROT_READ) == -1)
    		handle_error(&quot;mprotect&quot;);
    		a = *p;
    		printf(&quot;Now i can read the memory\n&quot;);
    
    	}
    /*	for (p = buffer;p&lt;=buffer+4*pagesize ;p++ ) 
    	{
    		//a = *(p);
    		*(p) = &#39;a&#39;;
    		printf(&quot;Writing at address %p\n&quot;,p);
    
    	}*/
    
    	printf(&quot;Loop completed\n&quot;);     /* Should never happen */
    	exit(EXIT_SUCCESS);
    }

The problem is that only the signal handler runs and I can&#39;t return to the main function after catching the signal.

  [1]: http://man7.org/linux/man-pages/man2/mprotect.2.html

How to write a signal handler to catch SIGSEGV?

I&#39;m developing C extensions from python and I obtain some segfaults (inevitable during the development...).

I&#39;m searching for a way to display at which line of code the segfault happens (an idea is like tracing every single line of code), how can I do that?

python tracing a segmentation fault

Why are hexadecimal numbers prefixed as `0x`?
 I understand the usage of the prefix but I don&#39;t understand the significance of why `0x` was chosen.

Why are hexadecimal numbers prefixed with 0x?

I often see `__WIN32`, `WIN32` or `__WIN32__`. I assume that this depends on the used preprocessor (either one from visual studio, or gcc etc).

Do I now have to check first for os and then for the used compiler? We are using here G++ 4.4.x, Visual Studio 2008 and Xcode (which I assume is a gcc again) and ATM we are using just `__WIN32__`, `__APPLE__` and `__LINUX__`.

Which Cross Platform Preprocessor Defines? (__WIN32__ or __WIN32 or WIN32 )?

It seems I often spend way too much time trying to get a #define macro to do exactly what i want. I&#39;ll post my current dilemma below and any help is appreciated. But really the bigger question is whether there is any utility someone could recommend, to quickly display what a macro is actually doing? It seems like even the slow trial and error process would go much faster if I could see what is wrong.

Currently, I&#39;m dynamically loading a long list of functions from a DLL I made. The way I&#39;ve set things up, the function pointers have the same nanes as the exported functions, and the typedef(s) used to prototype them have the same names, but with a prepended underscore. So I want to use a define to simplify assignments of a long long list of function pointers.

For example, In the code statement below, &#39;hexdump&#39; is the name of a typedef&#39;d function point, and is also the name of the function, while _hexdump is the name of the typedef. If GetProcAddress() fails, a failure counter in incremented. 

    if (!(hexdump = (_hexdump)GetProcAddress(h, &quot;hexdump&quot;))) --iFail;
 
So let&#39;s say I&#39;d like to replace each line like the above with a macro, like this...

    GETADDR_FOR(hexdump )

Well this is the best I&#39;ve come up with so far. It doesn&#39;t work (my // comment is just to prevent text formatting in the message)...


    // #define GETADDR_FOR(a) if (!(a = (#_#a)GetProcAddress(h, &quot;/&quot;&quot;#a&quot;/&quot;&quot;))) --iFail; 


And again, while I&#39;d APPRECIATE an insight into what silly mistake I&#39;ve made, it would make my day to have a utility that would show me the error of my ways, by simply plugging in my macro.
 

Any utility to test expand C/C++ #define macros?

Is there some way of getting optional parameters with C++ Macros? Some sort of overloading would be nice too.

Optional Parameters with C++ Macros

I&#39;d like to run a macro on every line in a selection, rather than totalling up the number of lines in my head. For instance, I might write a macro to transform:

    Last, First

Into

    First Last

and I&#39;d like it to run on all these lines:

    Stewart, John 
    Pumpkin, Freddy
    Mai, Stefan
    ...

Any ideas Vim gurus?

EDIT: This is just an example, obviously this is trivialy regexable, but there are other instances that come up that aren&#39;t quite so easy that I&#39;d prefer to use macros.

Vim Macro on Every Line of Visual Selection

What does `#pragma comment` mean in the following?

    #pragma comment(lib, &quot;kernel32&quot;)
    #pragma comment(lib, &quot;user32&quot;)


What does &quot;#pragma comment&quot; mean?

I&#39;m currently using GCC, but I discovered Clang recently and I&#39;m pondering switching. There is one deciding factor though - quality (speed, memory footprint, reliability) of binaries it produces - if `gcc -O3`can produce a binary that runs 1% faster, or Clang binaries take up more memory or just fail due to compiler bugs, it&#39;s a deal-breaker.

Clang boasts better compile speeds and lower compile-time memory footprint than GCC, but I&#39;m really interested in benchmarks/comparisons of resulting compiled software - could you point me to some pre-existing resources or your own benchmarks?

Clang vs GCC - which produces faster binaries?

I&#39;ve been playing with clang a while, and I stumbled upon &quot;test/SemaTemplate/dependent-template-recover.cpp&quot; (in the clang distribution) which is supposed to provide hints to recover from a template error.

The whole thing can be easily stripped down to a minimal example:

    template&lt;typename T, typename U, int N&gt; struct X {
        void f(T* t)
        {
            // expected-error{{use &#39;template&#39; keyword to treat &#39;f0&#39; as a dependent template name}}
            t-&gt;f0&lt;U&gt;();
        }
    };


The error message yielded by clang:

    tpl.cpp:6:13: error: use &#39;template&#39; keyword to treat &#39;f0&#39; as a dependent template name
             t-&gt;f0&lt;U&gt;();
                ^
                template 
    1 error generated.


... But I have a hard time understanding where exactly one is supposed to insert the `template` keyword to have the code to be syntactically correct?

Confusing Template error

I am considering the use of some C++11 features (like `auto` for instance) in some cross-platform projects (Windows+Mac). On Windows, Visual Studio supports parts of the upcoming C++11 standard that would allow me to simplify parts of the code base so naturally I would be interested in starting to use these features.

But as far as I am aware, the current XCode version (3.2.4 + GCC 4.2) does not support any C++11 features at all. Can I upgrade the GCC version or the CLang version somehow? Or should I just bite my tongue and wait for Apple to package a new version sometime in the future?


  

Can I use C++11 with Xcode?

I have saw the compiler option GNU99 and C99. What&#39;s the difference of them? Any detail documentation? (Clang, Xcode, Mac OS X)

What&#39;s the difference between GNU99 and C99 (Clang)?

I am having some difficulty compiling a C++ program that I&#39;ve written.

This program is very simple and, to the best of my knowledge, conforms to all the rules set forth in the C++ Standard.  I&#39;ve read over the entirety of ISO/IEC 14882:2003 twice to be sure.

The program is as follows:

![enter image description here][1]

Here is the output I received when trying to compile this program with Visual C++ 2010:
    
    c:\dev&gt;cl /nologo helloworld.png
    cl : Command line warning D9024 : unrecognized source file type &#39;helloworld.png&#39;, object file assumed
    helloworld.png : fatal error LNK1107: invalid or corrupt file: cannot read at 0x5172

Dismayed, I tried g++ 4.5.2, but it was equally unhelpful:

    c:\dev&gt;g++ helloworld.png
    helloworld.png: file not recognized: File format not recognized
    collect2: ld returned 1 exit status

I figured that Clang (version 3.0 trunk 127530) must work, since it is so highly praised for its standards conformance.  Unfortunately, it didn&#39;t even give me one of its pretty, highlighted error messages:

    c:\dev&gt;clang++ helloworld.png
    helloworld.png: file not recognized: File format not recognized
    collect2: ld returned 1 exit status
    clang++: error: linker (via gcc) command failed with exit code 1 (use -v to see invocation)

To be honest, I don&#39;t really know what any of these error message mean.

Many other C++ programs have source files with a _.cpp_ extension, so I thought perhaps I needed to rename my file.  I changed its name to _helloworld.cpp_, but that didn&#39;t help.  I think there is a very serious bug in Clang because when I tried using it to compile the renamed program, it flipped out, printed &quot;84 warnings and 20 errors generated.&quot; and made my computer beep a lot!

What have I done wrong here?  Have I missed some critical part of the C++ Standard?  Or are all three compilers really just so broken that they can&#39;t compile this simple program?  

  [1]: http://i.stack.imgur.com/JQXWL.png

Why is this program erroneously rejected by three C++ compilers?

At least some **C** preprocessors let you stringize the value of a macro, rather than its name, by passing it through one function-like macro to another that stringizes it:

    #define STR1(x) #x
    #define STR2(x) STR1(x)
    #define THE_ANSWER 42
    #define THE_ANSWER_STR STR2(THE_ANSWER) /* &quot;42&quot; */

Example use cases [here](http://everything2.com/title/stringize+macro+macro+hack).

This does work, at least in GCC and Clang (both with `-std=c99`), but I&#39;m not sure *how* it works in C-standard terms.

Is this behavior guaranteed by C99?  
If so, how does C99 guarantee it?  
If not, at what point does the behavior go from C-defined to GCC-defined?

How, exactly, does the double-stringize trick work?

I want to write a macro that spits out code based on the boolean value of its parameter. So say `DEF_CONST(true)` should be expanded into `const`, and `DEF_CONST(false)` should be expanded into nothing.

Clearly the following doesn&#39;t work because we can&#39;t use another preprocessor inside #defines:

    #define DEF_CONST(b_const) \
    #if (b_const) \
      const \
    #endif


How to use #if inside #define in the C preprocessor?

In the sake of debugging purposes, can I get the line number in **C**/C++ compilers?
(standard way or specific ways for certain compilers)

e.g

    if(!Logical)
        printf(&quot;Not logical value at line number %d \n&quot;,LineNumber);
        // How to get LineNumber without writing it by my hand?(dynamic compilation)



C/C++ line number

In **C**/C++

What happens to code placed between an `#if 0`/`#endif` block?

    #if 0
    
    //Code goes here
    
    #endif

Does the code simply get skipped and therefore does not get executed?

What exactly does an #if 0 ..... #endif block do?

As per subject. 

I have some constants hash defined like so:

    #define CONST 40

I&#39;ve set a breakpoint in my program. How do I print the value of that constant? (I know I can just look at the source code, but I want to be sure of it)



Content Type	Original Author	Original Content on Stackoverflow
Question	Pierre Bourdon	View Question on Stackoverflow
Solution 1 - C	Chris Suter	View Answer on Stackoverflow
Solution 2 - C	Pierre Bourdon	View Answer on Stackoverflow
Solution 3 - C	Bernd Elkemann	View Answer on Stackoverflow

What predefined macro can I use to detect clang?

C Problem Overview

C Solutions

Solution 1 - C

Solution 2 - C

Solution 3 - C

How to get anchor text/href on click using jQuery?

How Does Modulus Divison Work

Attributions