ubuntu OpenMP parallel for

OpenMP并行计算for循环

test.cpp

#include <iostream>
#include <stdio.h>
#include <vector>

using namespace std;

int main(){
    vector<int> a={1,2,3,4,5,6,7,8};
    vector<int> b={1,1,2};
    vector<int> c(8);

    #pragma omp parallel for 
    for(int i = 0; i < 8; i++)
    {
           c[i] = a[i] + b[i];
           printf("c[%d]=%d\n",i,c[i]);
    }
}

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From Stack Overflow[1] :

The OpenMP pragmas are only enabled when compiled with -fopenmp. Otherwise they are completely ignored by the compiler.

Therefore,you will need to add -fopenmp to the compilation of every single module that uses OpenMP. (As opposed to just the final linking step.)

g++ -std=c++11 -c test.cpp -o test.o -fopenmp
g++ test.o -o test -fopenmp -lpthread

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Environment Variable OMP_NUM_THREADS sets the number of threads[2]

export OMP_NUM_THREADS=4
./test

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My Results

c[0]=2 c[6]=8 c[5]=8 c[3]=6 c[2]=4 c[7]=10 c[1]=4 c[4]=6 

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for (auto &vi : vec) 这种for不能够用#pragma omp parallel for 来并行。要改成普通的int遍历。