posix pthread work on array elements in separate threads

Question

I am trying to learn posix and want to start from somethig simple. I want to work on array elements on different threads. My code is:

#include <iostream>
#include <pthread.h>
using namespace std;

static void* doWork(int* a, size_t s) {
    for(int i = 0; i < s; i++) {
        a[i] = a[i] * 2;
    }
    //return void;
}

void printIntArr(int* a, size_t s) {
    for(int i = 0; i < s; i++) {
        cout << a[i] << " ";
    }
    cout << endl;
}

int main() {

    int a[24];
    for(int i = 0; i < 24; i++) {
        a[i] = i;
    }

    printIntArr(&a[0], 24); //before

    //I want to make 2 threads, and pass first half and second half of the array to process
    pthread_t tA, tB;
    int resultA =  pthread_create(&tA, NULL, &doWork(&a[0],12), NULL);
    int resultB =  pthread_create(&tB, NULL, &doWork(&a[11],12), NULL);

    printIntArr(&a[0], 24); //after

    return 0;
}

I just want to perform doWork function on first and second half of the array on different threads. And yes my code does not compile.

Answer 1

#include <iostream>
#include <pthread.h>
using namespace std;

typedef struct {
    int* a;
    size_t s;
} Params;

static void* doWork(void * data) {
    Params * p = (Params *) data;
    for(int i = 0; i < p -> s; i++) {
        p ->a[i] = p ->a[i] * 2;
    }
    //return void;
    return data;
}

void printIntArr(int* a, size_t s) {
    for(int i = 0; i < s; i++) {
        cout << a[i] << " ";
    }
    cout << endl;
}

int main() {

    int a[24];
    for(int i = 0; i < 24; i++) {
        a[i] = i;
    }

    printIntArr(&a[0], 24); //before

    Params p1;
    p1.a = &(a[0]);
    p1.s = 12;

    Params p2;
    p2.a = &(a[11]);
    p2.s = 12;


    //I want to make 2 threads, and pass first half and second half of the array to process
    pthread_t tA, tB;
    int resultA =  pthread_create(&tA, NULL, doWork, (void *)&p1);
    int resultB =  pthread_create(&tB, NULL, doWork, (void *)&p2);

    pthread_join(tA, NULL);
    pthread_join(tA, NULL);

    printIntArr(&a[0], 24); //after

    return 0;
}

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If you are coding in c++, you may use this one: http://cpp.sh/4du5