g++ include paths on freebsd

Question

I installed gcc49 on FreeBSD10.1. I am trying to use it for C++11 development. However, every time I'm compiling some C++11 valid code (yes I use -std=c++11) that uses specific math functions, it spits out errors, such as

error: std::round is not a member of std
/usr/include/math.h 

For example, here:

#include <cmath>
#include <iostream>

int main()
{
    std::cout << std::round(10.1) << std::endl;
}

So it seems it tries to use the old include files that came with FreeBSD, and not the ones corresponding to the new gcc from /usr/local/lib/gcc49/include

I tried setting CPLUS_INCLUDE_PATH to /usr/local/lib/gcc49/include with no luck, the system still tries to search /usr/include instead.

I saw that this may be a bug in FreeBSD g++, Getting GCC in C++11 mode to work on FreeBSD however even using the -D_GLIBCXX_USE_C99 as suggested in https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194929 doesn't fix the problem for math functions.

The weirdest thing is that I can compile any other C++11 functions not from <cmath>, like std::stol, but have to use the -D_GLIBCXX_USE_C99 flag as mentioned in the bug report above.

Any idea how to make g++ fully functional with C++11 on FreeBSD 10.1?

Answer 1

It works out of box on 10.1, you shouldn't need any hacks. Of course, it only works with -std=c++11, as std::round is only available since 11 standard (see http://en.cppreference.com/w/cpp/numeric/math/round).

$ freebsd-version -ku
10.1-RELEASE
10.1-RELEASE
$ cat test.cc
#include <cmath>
#include <iostream>

int main() {
    std::cout << std::round(10.1) << std::endl;
}
$ g++5 -std=c++11 -o test test.cc
$ ./test
10

Note: gcc was compiled from ports, package was reported to not work. Probably because packages for 10.1 are at the time of writing compiled on 10.0, which still had c++11 compatibility issues.