How to get return value from child process to parent?

Question

I\'m supposed to return the sum of first 12 terms of Fibonacci series from child process to parent one but instead having 377, parent gets 30976.

Answer 1

If you can't use pipes, which would be the optimal solution here, you could save the result to a file that the parent would read from. Pass the name of the file to save the result to from parent to child. In your child process, you would do:

int main(int argc, char *argv[])
{
    int fib_sum=0;
    if (argc <= 1)
    {
        print_usage();
        return 1;
    }
    //... calculate fib_sum
    FILE *f = fopen(argv[1], "w");
    if (f == NULL)
    {
        printf("Error opening file!\n");
        return 1;
    }
    fprintf(f, "%d", fib_sum);
    return 0;
}

Then in your parent process:

int n = 0;
FILE* f;
//... spawn child and wait
FILE *f = fopen(file_name, "r");
fscanf(f, "%d", &n);