hello_thread.c

// Hello World for POSIX-threads
// compile using: gcc -o hello_thread hello_thread.c -lpthread
// then run like this: ./hello_thread 4
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

void *hello_world(void *thread_id) {
    printf("Hello world from thread: %ld!\n", (long)thread_id); 
}


int main(int argc, char** argv) {

    if (argc < 2) {
        printf("Usage: hello_thread num_threads\n");
        pthread_exit(NULL);
    }
    int num_threads = atoi(argv[1]);
    pthread_t threads[num_threads];

    printf("In main thread...\n");
    long i;
    for (i = 0; i < num_threads; i++) {
        printf("Creating thread %ld\n", i);
        int ret = pthread_create(&threads[i], NULL, &hello_world, (void *)i);

        if(ret != 0) {
                printf("Error: pthread_create() failed for thread %ld\n", i);
                exit(EXIT_FAILURE);
        }
    }

    pthread_exit(NULL);
}