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.

score 58 · Answer 1 · answered Nov 03 '08 at 16:59

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.

score 33 · Accepted Answer · answered Nov 03 '08 at 16:59

33

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

answered Nov 03 '08 at 16:59

PierreBdR

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Unfortunately this code fails with the clang compiler, which defines `__GNUC__`, but doesn't include `features.h`. – Gil May 22 '13 at 13:19
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Well, this code is to know the version of GCC, so it's not surprising that it fails if clang partially impersonate GCC. – PierreBdR May 28 '13 at 11:44
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Sorry, it seems I was wrong. The `features.h` include is simply a Linux specific thing, and should not be relied on for any code that is intended to compile on other platforms. – Gil May 29 '13 at 09:33
This code has been tested on Mac OS X, Windows (MingW32 and MingW64) and Linux ... I am fairly sure features.h is a GCC specific include file. – PierreBdR May 29 '13 at 10:19
4

The file is not directly from GCC, but rather from the glibc project. Surely, you can't assume the existence of this file based on the current compiler. – Gil May 29 '13 at 12:38

score 22 · Answer 3 · edited May 29 '15 at 18:18

22

As a side note:

To find all the predefined macros:

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

edited May 29 '15 at 18:18

idmean

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answered Nov 03 '08 at 17:40

Martin York

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Without creating an empty file: g++ -E -dM - – JesperE Nov 03 '08 at 19:25
1

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. – Lawrence Aiello May 29 '15 at 17:19
@LawrenceAiello: Your comment is only 7 years late. – Martin York May 29 '15 at 19:10
@LawrenceAiello: Seems to have been edited just adding code quotes to the one line (and was approved). – Martin York May 29 '15 at 19:13

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

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