c++ - 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.