Thread example in C

threads.c

// To compile in linux with gcc
// compile: gcc -pthread <filename>.c -o <filename>
// run: ./<filename>

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <string.h>

// Struct for args aggrupation
typedef struct thread_data {
    int a;
    int b;
} thread_data;

void* writeToFileWithThread(void* x);

int main(void) {
    // Declarate thread with id
    pthread_t t;

    // Setting args and capture value
    thread_data arg;
    arg.a = 15;
    arg.b = 18;

    void* captureVal = NULL;

    // Create thread 
    // Args: thread id, attributes, start function, arguments passed to start
    pthread_create(&t, NULL, writeToFileWithThread, &arg);

    // Waits for thread terminantion
    // Args: thread id, reference to capture value returned by thread
    pthread_join(t, &captureVal);

    printf("Returned message by thread: %s\n", (char*)captureVal);
    
    return 0;
}

void* writeToFileWithThread(void* x) {
	// Casting void ptr to known mem size
    thread_data* nums = (thread_data *) x;

	// File opening
    FILE *f = fopen("file.txt", "w");

	// Handling not found file (must exist in current dir)
    if(f == NULL) {
        printf("Error opening file");
        exit(1);
    }

    // Writing to file and closing
    fprintf(f, "Sum: %d\n", nums->a + nums->b);
    fprintf(f, "Sub: %d\n", nums->a - nums->b);
    fprintf(f, "Mul: %d\n", nums->a * nums->b);

    fclose(f);

	// Returning value to parent thread
    return (void*) "success";
}