pthread c++ example with output

#include <iostream>
#include <pthread.h>

#define NUM_THREADS 5

void PrintHello(void threadid) {
    long tid;
    tid = (long)threadid;
    std::cout << "Hello World! Thread ID, " << tid << std::endl;
    pthread_exit(NULL);
}

int main () {
    pthread_t threads[NUM_THREADS];
    int rc;
    long t;
    for(t = 0; t < NUM_THREADS; t++) {
        std::cout << "Creating thread, " << t << std::endl;
        rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
        if (rc) {
            std::cout << "Error: unable to create thread, " << rc << std::endl;
            exit(-1);
        }
    }
    pthread_exit(NULL);
}

Explanation:

• #include <iostream> and #include <pthread.h>: Includes the necessary libraries for input/output and POSIX threads.
• #define NUM_THREADS 5: Defines the number of threads to be created as 5.

The function void PrintHello(void threadid) is the function that will be executed by each thread:

• void PrintHello(void threadid): This function takes a void pointer as an argument and casts it to a long variable tid. This function prints "Hello World! Thread ID" followed by the tid value and exits the thread.

In the main() function:

• pthread_t threads[NUM_THREADS];: Declares an array of pthreads to hold thread IDs.
• int rc; and long t;: Declare variables for error checking and loop iteration.
• for(t = 0; t < NUM_THREADS; t++): Loops to create multiple threads.
• std::cout << "Creating thread, " << t << std::endl;: Outputs the message indicating the creation of a thread with its respective ID.
• rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);: Creates a new thread with pthread_create passing the thread ID, attributes (NULL for default), function to be executed (PrintHello), and the argument t.
• if (rc) { std::cout << "Error: unable to create thread, " << rc << std::endl; exit(-1); }: Checks if thread creation fails and prints an error message with the return code.
• pthread_exit(NULL);: Exits the main thread after all threads are created.