omp_get_num_threads

Definition

omp_get_num_threads returns the number of threads in the current OpenMP region. If this function is called outside a parallel region, only the master thread is present hence the value returned is 1. Although spellings are close, do not confuse this function with omp_get_thread_num.

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int omp_get_num_threads();

Returned value

The number of threads contained in the current region.

Example

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#include <stdio.h>
#include <stdlib.h>
#include <omp.h>

/**
 * @brief Illustrates how to get the number of threads.
 * @details This code prints the number of threads at two specific locations:
 *     1) Outside an OpenMP parallel region
 *     2) Inside an OpenMP parallel region
 **/
int main(int argc, char* argv[])
{
    // Tell OpenMP to use 4 threads in parallel regions
    omp_set_num_threads(4);

    // 1) Outside the OpenMP parallel region
    printf("Outside the OpenMP parallel region, we are %d threads.\n", omp_get_num_threads());

    // Create the OpenMP parallel region, which will contain 4 threads
    #pragma omp parallel
    {
        // 2) Inside the OpenMP parallel region
        printf("Inside the OpenMP parallel region, we are %d threads.\n", omp_get_num_threads());
    }

    return EXIT_SUCCESS;
}