POSIX allows for <math.h> functions to also be defined as macros.
Currently, only log2 and log2f are so defined.
These macros pose problems with a few projects which define their own
static/inline/template log2() (off the top of my head, I can think of 2:
the CRAN rgl module, and OpenCV; both are C++). Of course, those can be
fixed with an #undef log2 after the #include's.
However, I just encountered tonight a much larger conflict: OpenMP/C++
and <math.h> are incompatible. STC attached:
$ g++ -D_GLIBCXX_PARALLEL -fopenmp openmp.cxx -lgomp
In file included from
/usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/parallel/algobase.h:46,
from
/usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/bits/stl_algobase.h:1137,
from
/usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/bits/char_traits.h:46,
from /usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/ios:46,
from
/usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/ostream:45,
from
/usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/iostream:45,
from openmp.cxx:7:
/usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/parallel/base.h:112:
error: expected `)' before ‘/’ token
It gets even worse if you #include <algorithm> as well, and no, it
doesn't help to #include <cmath>, although moving the math include after
all other includes does work.
I see two possible solutions:
1) Make the log2 macros dependent on #ifndef __cplusplus;
2) Make the parallel/* headers #undef log2 and log2f.
Thoughts?
Yaakov
// http://en.wikipedia.org/wiki/OpenMP#Hello_World
// with an #include <math.h>
// if you also #include <algorithm>, this *really* blows up
#include <omp.h>
#include <iostream>
#include <cmath>
int main (int argc, char *argv[]) {
int th_id, nthreads;
#pragma omp parallel private(th_id)
{
th_id = omp_get_thread_num();
std::cout << "Hello World from thread" << th_id << "\n";
#pragma omp barrier
if ( th_id == 0 ) {
nthreads = omp_get_num_threads();
std::cout << "There are " << nthreads << " threads\n";
}
}
return 0;
}
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