How to test the current version of GCC at compile time?

Question

I would like to include a different file depending on the version of GCC. More precisely I want to write:

#if GCC_VERSION >= 4.2
#  include <unordered_map>
#  define EXT std
#elif GCC_VERSION >= 4
#  include <tr1/unordered_map>
#  define EXT std
#else
#  include <ext/hash_map>
#  define unordered_map __gnu_cxx::hash_map
#  define EXT __gnu_cxx
#endif

I don't care about gcc before 3.2.

I am pretty sure there is a variable defined at preprocessing time for that, I just can't find it again.

Answer 1

There are a number of macros that should be defined for your needs:

__GNUC__              // major
__GNUC_MINOR__        // minor
__GNUC_PATCHLEVEL__   // patch

The version format is major.minor.patch, e.g. 4.0.2

The documentation for these can be found here.

Answer 2

Ok, after more searches, it one possible way of doing it is using __GNUC_PREREQ defined in features.h.

#ifdef __GNUC__
#  include <features.h>
#  if __GNUC_PREREQ(4,0)
//      If  gcc_version >= 4.0
#  elif __GNUC_PREREQ(3,2)
//       If gcc_version >= 3.2
#  else
//       Else
#  endif
#else
//    If not gcc
#endif

Answer 3

As a side note:

To find all the predefined macros:

• Create empty file t.cpp
• g++ -E -dM t.cpp