Hello All,

         I understood that __FUNCTION__ is a preprocessor macro, which
will substitute a file name. Similar to __FILE__ and __LINE__.

         1) I have written a small code, only for __FUNCTION__ it
prints as unknown why? What is the difference between __FILE__ and
__FUNCTION__. When I comment #ifndef __FUNCTION block it prints the
file name.
         2) Where do I get a list of all the preprocessor macros.

#include <stdio.h>
#include <errno.h>

#ifndef __LINE__
#define __LINE__ 0
#endif

#ifndef __FILE__
#define __FILE__ "Unknown"
#endif

#ifndef __FUNCTION__
#define __FUNCTION__ "Unknown"
#endif

int assert(int bool, int line, char *file, char *fun)
{
        char mesg[100];
        sprintf(mesg, "line: %d, file: %s, function: %s\nError ", line, file,
fun);
        if(bool){
                perror(mesg);
                errno = 0;
        }
        return 1;

int main()
{
        char info[50];
        FILE *fp;

        errno = 0;
        fp = fopen("ex.dat", "r");
        assert(fp == NULL, __LINE__ - 1, __FILE__, __FUNCTION__);

        fp = fopen("t.c", "r");
        assert(errno != 0, __LINE__, __FILE__, __FUNCTION__);
        return 1;

bye,
Sobhan

Hi,

C99 introduced the identifier __func__ to provide the function name as a
string. __FUNCTION__ would have to be implementation specific and you'll
need to ask in a newsgroup for your compiler.

__func__ is not a preprocessor macro like __FILE__ and __LINE__, but an
identifier for the function in which it is used. It doesn't have any
meaning outside of a function body. If your compilers use of
__FUNCTION__ is similar this might be why your (re)definition occurs.
Note in C99 defining __func__ yourself results in undefined behaviour.

To get a list of current macro definitions, you could do a google search
for "N869", which is a copy of the committee draft for the C99 spec. It
differs slightly from the final C99 spec, but it is free. (You can
purchase a copy of the C99 spec from http://www.ansi.org )

Or you could have a look at Stan Browns' compilation of 'Identifiers not
to use in C programs'
http://www.oakroadsystems.com/tech/c-predef.htm
It doesn't cover C99, but does allow you to pause for thought if you're
writing portable C code.

        Regards
        Des Walker

__FUNCTION__ is a GCC-specific extension.  Please read the node
"Function Names" in the GCC Info file or "Function Names as Strings"
in the printed manual; it's all explained there.

__FUNCTION__ is not a preprocessor macro, because the preprocessor
does not know about functions.

C99 has a similar identifier __func__, which isn't a preprocessor
macro either.

If you're using GCC on Unix, you can do this:

  gcc -E -dM -xc /dev/null

i.e., preprocess an empty file as C and list all defined macros when
finished.  Many of those macros are not in any standard.

In article <47295485.0110190255.7f389...@posting.google.com>
           sob...@eudoramail.com "Sobhan Vezzu" writes:

The C language doesn't define anything called __FUNCTION__ although it does
define __FILE__ and __LINE__

Perhaps because it isn't defined?

You compiler may provide __FUNCTION__ as an extension. Most likely it
will expand to the name of the function containing it. If it isn't
in a function then it won't be able to expand to anything. The new
C standard C99 does introduce something like this but it is called
__func__ and it is *not* a macro, it acts like the name of a static
variable within that function.

Any good tutorial book on C should give one.

There is a standard defined macro named assert(), this is an unwise name
to define in your code.

--
-----------------------------------------
Lawrence Kirby | f...@genesis.demon.co.uk
Wilts, England | 70734....@compuserve.com
-----------------------------------------

Well, that was interesting.  Adapted to MSDOS/DJGPP, it gives:

c:\dnld\scratch>gcc -E -dM -xc nul
#define __DJGPP_MINOR 3
#define __i386__ 1
#define __GO32__ 1
#define __i386 1
#define GO32 1
#define __GNUC_MINOR__ 95
#define __DJGPP__ 2
#define __tune_pentium__ 1
#define __DJGPP 2
#define i386 1
#define __MSDOS 1
#define __MSDOS__ 1
#define __unix 1
#define DJGPP_MINOR 3
#define __unix__ 1
#define __GNUC__ 2
#define DJGPP 2
#define MSDOS 1
#define __DJGPP_MINOR__ 3
#define unix 1
#define __GO32 1

--
Chuck F (cbfalco...@yahoo.com) (cbfalco...@XXXXworldnet.att.net)
   Available for consulting/temporary embedded and systems.
   (Remove "XXXX" from reply address. yahoo works unmodified)
   mailto:u...@ftc.gov  (for spambots to harvest)

"Kalle Olavi Niemitalo" <k...@iki.fi> wrote:

Why only on Unix?

C:\>gcc -ansi -E -dM -xc /dev/null
#define __STRICT_ANSI__ 1
#define __i386__ 1
#define _X86_ 1
#define __i386 1
#define __i686 1
#define __GNUC_MINOR__ 95
#define __declspec(x) __attribute__((x))
#define __CYGWIN__ 1
#define __pentiumpro 1
#define __pentiumpro__ 1
#define __stdcall __attribute__((__stdcall__))
#define __unix 1
#define __unix__ 1
#define __i686__ 1
#define __GNUC__ 2
#define __cdecl __attribute__((__cdecl__))
#define __CYGWIN32__ 1

Ralmin.