Error building Boost 1.49.0 with GCC 4.7.0

Question

I'm trying to build Boost 1.49.0 using GCC 4.7.0 (MinGW). I keep getting the following error message several dozen times:

c:\tools\mingw\bin../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/c++/4.7.0/cmath:1096:11: error: '::hypot' has not been declared

Line 1096 of cmath contains

using ::hypot;

cmath includes math.h which declares the hypot function as

extern double __cdecl hypot (double, double); /* in libmoldname.a */

In both files, a couple of lines after the ones quoted above, are identical statements for the hypotl function (except the type is long double instead of double) and that one seems happy.

Any ideas why I am getting this error?

Answer 1

The answer by @Praetorian correctly identifies the problem. On the other hand, the Python headers are technically meant to come before any others. In addition, sometimes the accepted solution does not work or is inconvenient in the build system, so I came up with an alternate solution. Add the following flag to the call to g++:

-D_hypot=hypot

This makes it so that the harmful macro in the Python headers becomes a no-op, and the compilation error goes away.

Answer 2

Found the answer in this forum post. It seems that pyconfig.h has the following lines:

#if defined(__GNUC__) && defined(_WIN32)
// ...
#define hypot _hypot
// ...
#endif /* GNUC */

but cmath included with MinGW expects the function to be named hypot and not _hypot, which causes the compilation errors.

The fix was to include the following to my bjam command line's cxxflags option

bjam ... cxxflags="-include cmath "

This indicates that g++ should include the cmath header at the beginning of every source file.