OpenMP, macros, and #define

Sometimes you need to include directives in macros. The classic example would be putting OpenMP directives into macros. The "obvious" way of doing this is:

#define BARRIER \
#pragma omp barrier

void foo()
{
  BARRIER
}

Which produces the following error:

"test.c", line 6: invalid source character: '#'
"test.c", line 6: undefined symbol: pragma
"test.c", line 6: syntax error before or at: omp

Fortunately C99 introduced the _Pragma mechanism to solve this problem. So the functioning code looks like:

#define BARRIER \
_Pragma("omp barrier")

void foo()
{
  BARRIER
}