clang: "omp_set_num_threads" fail

Asked Oct 13 '16 at 10:07

Active Jul 12 '22 at 15:31

Viewed 1,463 times

#include <omp.h>
#include <stdio.h>
int main() {
    omp_set_num_threads(4);

#pragma omp parallel
    printf("Hello World\n");
}

$ clang-omp++ openmp.cpp

I get

Undefined symbols for architecture x86_64: "_omp_set_num_threads",

referenced from: _main in openmp-7ace00.o ld: symbol(s) not found for architecture x86_64 clang-3.5: error: linker command failed with exit

code 1 (use -v to see invocation)

Program compiles after omp_set_num_threads(4); removed.

$ clang -v

clang version 3.8.0 (http://llvm.org/git/clang.git

68170291648f0112957a8b3d6912a1a1fed81965) (http://llvm.org/git/llvm.git 92ca4a0cd38e8f17e62ecf6e93a44c8ecf098b12)

Target: x86_64-apple-darwin16.0.0

Thread model: posix

How do I set OpenMP thread number?

edited Oct 13 '16 at 10:16

asked Oct 13 '16 at 10:07

Rahn

4,787
4
31
57

Do you compile with -fopenmp? – Trevir Oct 13 '16 at 10:22
@Trevir No, I compile with `clang-omp++`, `-fopenmp` doesn't work for me. – Rahn Oct 13 '16 at 10:34
-> clang-3.5: error, this clang version doesn't support openmp. Maybe something is wrong with your libraries – Trevir Oct 13 '16 at 10:36
Have a look here... http://stackoverflow.com/a/39983933/2836621 – Mark Setchell Oct 13 '16 at 10:59
@MarkSetchell No, that's not my case. – Rahn Oct 13 '16 at 11:47
@Trevir Is it about retrieving clang from HomeBrew? – Rahn Oct 13 '16 at 14:09
If you are compiling without -fopenmp then the OpenMP pragmas will be ignored and the OpenMP runtime won't be added to link command (hence the lack of a definition for omp_set_num_threads). So, your comment at 2 is the critical one. You need to fix your system so that -fopenmp does work! – Jim Cownie Oct 17 '16 at 08:14

clang: "omp_set_num_threads" fail

0 Answers0