Boost C++ Libraries: Ticket #9240: boost 1.54.0 math/constants/constants.hpp doesn't compile with gcc 4.8 with c++11 if you undef __STRICT_ANSI__

John Maddock — Sat, 12 Oct 2013 08:43:29 GMT

I can reproduce, but don't see any way to fix this - if you undef __STRICT_ANSI__ then you remove all means for us to detect that GCC specific extensions are disabled. Unless you know of another way?

richardg.work@… — Wed, 20 Nov 2013 21:17:44 GMT

You could use GXX_EXPERIMENTAL_CXX0X, which gcc only defines when you use -std=c++11 (or -std=c++0x)

John Maddock — Tue, 26 Nov 2013 18:35:35 GMT

You could use GXX_EXPERIMENTAL_CXX0X, which gcc only defines when you use -std=c++11 (or -std=c++0x)

No that doesn't work, __float128 along with 128-bit literals are supported or not as follows:

-std=c++-03   Yes
-std=gnu++-03 Yes
-std=c++-11   No
-std=gnu++-11 Yes

The last two both define __GXX_EXPERIMENTAL_CXX0X__, the only difference between them that I can see from using g++ -E -dM is __STRICT_ANSI__. Indeed, GCC's own headers use __STRICT_ANSI__ to differentiate between these two modes, so I still believe that what you're doing is basically a mistake.

Tue, 26 Nov 2013 19:46:58 GMT

There are many reasons for undefining STRICT_ANSI as it's widely used in system headers. If you're using boost in a large legacy codebase, and I expect it's common for people porting large codebases from C++03 to C++11. This bug is really the fault of gcc for overloading the meaning of STRICT_ANSI to imply their special features are enabled/disabled. GCC doesn't own the STRICT_ANSI #define, it's owned by the ISO standard.

Regardless, since the issue is with the numeric literal not the float128 type, is there a different, more compatible way to specify the literals?

status changed; resolution set

John Maddock — Mon, 23 Dec 2013 10:06:01 GMT

status new → closed
resolution → fixed

Fixed in Git develop: I've added and documented two config macros: BOOST_MATH_USE_FLOAT128 and BOOST_MATH_DISABLE_FLOAT128 which explicitly enable/disable this feature. Defining the latter macro should fix things for your use case.