Check glibc version for a particular gcc compiler

I have two gcc compilers installed on my system, one is gcc 4.1.2 (default) and the other is gcc 4.4.4. How can I check the libc version used by gcc 4.4.4, because /lib/libc.so.6 shows the glibc used by gcc 4.1.2, since it is the default compiler.

Write a test program (name it for example glibc-version.c):

#include <stdio.h>
#include <stdlib.h>
#include <gnu/libc-version.h>

int main(int argc, char *argv[]) {
  printf("GNU libc version: %s\n", gnu_get_libc_version());
  exit(EXIT_SUCCESS);
}

and compile it with the gcc-4.4 compiler:

gcc-4.4 glibc-version.c -o glibc-version

When you execute ./glibc-version the used glibc version is shown.

even easier

use ldd --version

This should return the glibc version being used i.e.

$ ldd --version

ldd (GNU libc) 2.17
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO

...

which is the same result as running my libc library

$ /lib/libc.so.6 


GNU C Library (GNU libc) stable release version 2.17, by Roland McGrath et al.
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.

...

Use -print-file-name gcc option:

$ gcc -print-file-name=libc.so
/usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libc.so

That gives the path. Now:

$ file /usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libc.so
/usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libc.so: ASCII C program text

$ cat /usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libc.so
/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )

Looks like a linker script. libc is special on Linux in that it can be executed:

$ /lib64/libc.so.6
GNU C Library stable release version 2.13, by Roland McGrath et al.
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.5.1 20100924 (Red Hat 4.5.1-4).
Compiled on a Linux 2.6.35 system on 2011-08-05.
Available extensions:
    Support for some architectures added on, not maintained in glibc core.
    The C stubs add-on version 2.1.2.
    crypt add-on version 2.1 by Michael Glad and others
    GNU Libidn by Simon Josefsson
    Native POSIX Threads Library by Ulrich Drepper et al
    BIND-8.2.3-T5B
    RT using linux kernel aio
libc ABIs: UNIQUE IFUNC
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.

gnu_get_libc_version identifies the runtime version of the GNU C Library.

If what you care about is the compile-time version (that is, the version that provided the headers in /usr/include), you should look at the macros __GLIBC__ and __GLIBC_MINOR__. These expand to positive integers, and will be defined as a side-effect of including any header file provided by the GNU C Library; this means you can include a standard header, and then use #ifdef __GLIBC__ to decide whether you can include a nonstandard header like gnu/libc-version.h.

Expanding the test program from the accepted answer:

#include <stdio.h>
#ifdef __GLIBC__
#include <gnu/libc-version.h>
#endif

int
main(void)
{
#ifdef __GLIBC__
  printf("GNU libc compile-time version: %u.%u\n", __GLIBC__, __GLIBC_MINOR__);
  printf("GNU libc runtime version:      %s\n", gnu_get_libc_version());
  return 0;
#else
  puts("Not the GNU C Library");
  return 1;
#endif
}

When I compile and run this program on the computer I'm typing this answer on (which is a Mac) it prints

Not the GNU C Library

but when compiled and run on a nearby Linux box it prints

GNU libc compile-time version: 2.24
GNU libc runtime version:      2.24

Under normal circumstances, the "runtime" version could be bigger than the "compile-time" version, but never smaller. The major version number is unlikely ever to change again (the last time it changed was the "libc6 transition" in 1997).

If you would prefer a shell 'one-liner' to dump these macros, use:

echo '#include <errno.h>' | gcc -xc - -E -dM | 
    grep -E '^#define __GLIBC(|_MINOR)__ ' | sort

The grep pattern is chosen to match only the two macros that are relevant, because there are dozens of internal macros named __GLIBC_somethingorother that you don't want to have to read through.

I doubt if you have more than one glibc installed in your system.But ldd -v <path/to/gcc-4.x> should give you the glibc used.