On 27 July 2015 at 21:22, Edward Diener wrote: > On 7/27/2015 10:57 AM, Jonathan Wakely wrote: >> >> On 27 July 2015 at 14:48, Edward Diener wrote: >>> >>> On 7/27/2015 4:34 AM, Jonathan Wakely wrote: >>>> >>>> >>>> On 27 July 2015 at 05:17, Edward Diener wrote: >>>>> >>>>> >>>>> >>>>> Try >>>>> >>>>> #if defined(__GXX_EXPERIMENTAL_CXX0X__) || (__cplusplus >= 201103L) >>>>> // C++11 is in effect >>>>> #endif >>>> >>>> >>>> >>>> >>>> GCC 4.8 defines __cplusplus to the correct YYYYMMDD value so this is >>>> not necessary. >>>> >>> >>> I meant it as a general solution for any version of gcc. It is what Boost >>> config uses. >> >> >> But it doesn't help if you run the preprocessor in C mode not C++, >> since neither will be defined :-) > > > How is it possible to be compiling for C++11 when running in C mode ? > > In other words it does work since a C++11 compile will never be defined when > running in C mode, which is certainly what is wanted. See the first mail in the thread, which attempted to use the preprocessor to detect whether C++11 is supported like so: $ g++ -std=c++11 -dM -E - < /dev/null | grep cplusplus cc1.exe: warning: command line option '-std=c++11' is valid for C++/ObjC++ but not for C [enabled by default]= This is running the preprocessor in C mode. Checking for __GXX_EXPERIMENTAL_CXX0X__ here won't help, because it's still using the preprocessor in C mode, i.e. this still fails: $ g++-4.4.7 -std=c++0x -dM -E - < /dev/null | egrep 'cplusplus|EXPERIMENTAL' cc1: warning: command line option "-std=c++0x" is valid for C++/ObjC++ but not for C Whereas this works, because it runs the preprocessor in C++ mode: $ g++-4.4.7 -std=c++0x -dM -E -x c++ - < /dev/null | egrep 'cplusplus|EXPERIMENTAL' #define __GXX_EXPERIMENTAL_CXX0X__ 1 #define __cplusplus 1 That's what I meant about running the preprocessor in C mode, not C++ mode.
