Using OpenMP with C++11 range-based for loops?

Is there any counter-indication to doing this ? Or is the behavior well specified?

#pragma omp parallel for
for(auto x : stl_container)
{
   ...
}

Because it seems that OpenMP specification is only valid for c++98 but I guess there might be more incompatibilities due to C++11 threads, which are not used here. I wanted to be sure, still.

The OpenMP 4.0 specification was finalised and published several days ago here. It still mandates that parallel loops should be in the canonical form (§2.6, p.51):

> for (init-expr; test-expr; incr-expr) structured-block

The standard allows for containers that provide random-access iterators to be used in all of the expressions, e.g.:

#pragma omp parallel for
for (it = v.begin(); it < v.end(); it++)
{
   ...
}

If you still insist on using the C++11 syntactic sugar, and if it takes a (comparatively) lot of time to process each element of stl_container, then you could use the single-producer tasking pattern:

#pragma omp parallel
{
   #pragma omp single
   {
      for (auto x : stl_container)
      {
         #pragma omp task
         {
            // Do something with x, e.g.
            compute(x);
         }
      }
   }
}

Tasking induces certain overhead so it would make no sense to use this pattern if compute(x); takes very little time to complete.

OpenMP 5.0 adds the following line on page 99, which makes a lot of range-based for loops OK !

> 2.12.1.3 A range-based for loop with random access iterator has a canonical loop form.

Source : https://www.openmp.org/wp-content/uploads/OpenMP-API-Specification-5.0.pdf