Stack Exchange
Where is the body of function in header files of C
When i look at header files files of C(or C++)
for example 
stdio.h
there are definition of some functions
for example
_CRTIMP FILE* __cdecl __MINGW_NOTHROW fopen (const char*, const char*);
_CRTIMP FILE* __cdecl __MINGW_NOTHROW freopen (const char*, const char*, FILE*);
_CRTIMP int __cdecl __MINGW_NOTHROW fflush (FILE*);
_CRTIMP int __cdecl __MINGW_NOTHROW fclose (FILE*);
/* MS puts remove & rename (but not wide versions) in io.h  also */
_CRTIMP int __cdecl __MINGW_NOTHROW remove (const char*);
_CRTIMP int __cdecl __MINGW_NOTHROW rename (const char*, const char*);
_CRTIMP FILE* __cdecl __MINGW_NOTHROW tmpfile (void);
_CRTIMP char* __cdecl __MINGW_NOTHROW tmpnam (char*);

Can you tell me
where are the body of theese functions.....

You do not even have to open any files on your system. Sometimes they are posted on the web as html files like this https://docs.google.com/viewer?pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxyeWFuYnJvb21maWVsZHxneDo1MmVlMGE3ZWY0M2U4ODk3&docid=ceac0a02f360520a8550d5bb6203700d%7C434bbc224d60a89bc0bbca61eea5d16d&chan=EQAAACOxrV%2B9nw4spSLems6Hb5e7CThUhkFvzhJxKF5%2BcOXC&a=v&rel=zip;z428;io.h or this https://svn.janelia.org/penglab/projects/vaa3d/trunk/v3d_main/common_lib/mingw32/include/stdio.h

Normally, as @Daren Thomas said, you'll have .c file matching the hader (.h file). However, regarding the standard library, these c files come precompiled and put together in a big file (for example, libc.so), and can be found in the lib folder of your compiler in Windows, and in the /usr/lib folder in Unix/Linus OS's.
For g++, the libc library is used as the standard library. You can download the package from here:
http://ftp.gnu.org/gnu/glibc/glibc-2.9.tar.gz
... and browse the source code for all functions.

Normally, the body is in a file with the same name, but ending in .c or .cpp.
Sometimes you don't have the source code, so look for .o, which contains the object code for your library, i.e. the compiled library. The header file is then a kind of API description.
In special cases like stdio.h, which are part of the standard library, the location of these files are implementation specific. In fact, the existence of these files are implementation specific too - I believe a compiler may choose to provide this information however it pleases to do so.

but there is not a file with name
stdio.c or
stdio.cpp or
stdio.o

@namco: because the implementation is in the runtime libaries. For MS, the libraries are these: http://msdn.microsoft.com/en-us/library/abx4dbyh(v=vs.71).aspx

And for linux, a lot of the header files provide prototypes for system calls, which aren't implemented in C at all are are basically inline assembly or kernel level code

@namco Also, the compiler manufacturer usually isn't too happy to give away his whole source code/livelihood for free. Nowadays some do however, as their profit isn't related to the implementation of the standard libraries. And then of course there is always open-source GCC, which is free.
