OMP for loop with no initialization

Question

I am trying to run a code snippet using openmp, but it gives compile error as there is no initialization in the for loop. The iterator class is defined here. I am not able to figure out how can I initialize inside the for loop.

I am not an expert in C++, so I would appreciate any help.

ntHashIterator itr(seq, h, k);
#pragma omp parallel for  
for(; itr != itr.end(); ++itr){ 
   std::cout << (*itr)[0] << std::endl; 
}

Try for (ntHashIterator itr = ntHashIterator(seq, h, k); itr != itr.end(); ++itr) — acraig5075
– acraig5075, Commented Jun 26, 2018 at 5:56
Thanks @acraig5075 !! I tried that, but it was giving invalid controlling predicate error. I think the answer below explains that. — viz12
– viz12, Commented Jun 26, 2018 at 15:02

Daniel Langr · Accepted Answer · 2018-06-26 06:06:52Z

2

OpenMP requires loops to be in so-called canonical loop form. Moreover, it can works with iterators, but they have to be of a random-access iterator type. Which doesn't seem to be your case, since your nHashIterator does not support + and += operators. See the OpenMP specifications for more details.

Anyway, it's hard to tell more, since you are not providing enough details such as a compiler and OpenMP version which it supports.

answered Jun 26, 2018 at 6:06

Daniel Langr

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2 Comments

Zulan Over a year ago

That the canonical loop form also requires it < end() as loop condition even if it is a random access iterator.

viz12 Over a year ago

Thanks Daniel !! I got the idea now. I am using gcc (GCC) 7.3.0.

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