How to fix segment Fault Error in Terminal?

Question

Output of the program

I'm trying to compile my code and I feel it works perfectly fine and I can get it to compile. However, when I do I'm getting Segment fault error and I don't see where the error is in my code.

The error i'm getting is Segment fault: 11 I've looked this up and I know it has to do with memory allocation but haven't been able to find where in the code do I need to fix my memory allocation and fix the errors I have on here.

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>

/*The Main Function Start*/
void main(int argc, char *argv[])
{
    /*Storing The Process Id*/
    pid_t pid;
    int j;
    int status = 0;


    /*process of forking*/

    if (argc == 1){
        fprintf(stderr,"Usage: ./hw1 <starting value>\n");
    }
    int n = atoi(argv[1]);
    pid=fork();
    if (pid == -1){
        printf("Error in forking....\n");
        exit(0);
    }
    /*Child process*/
    if (pid == 0)
    {
        printf("Child PID: %d\n",getpid());

        while (n != 1){
            printf("%d ",n);
            if (n % 2 == 0){
                n = n/2;
            }
            else {
                n = 3*n + 1;
            }

        }
        printf("1\n");
    }
    else{
        printf("Parent PID: %d\n",getpid());
        /*Waiting for the child to finish*/
        wait(0);
    }
    exit(0);
}

Answer 1

I only get a segfault when I'm not passing any parameters, because

int n = atoi(argv[1]);

would be doing essentially atoi(NULL), because argv[1] would be NULL.

if (argc != 2){
        fprintf(stderr, "usage: %s <starting value>\n", argv[0]);
        return 1; // <- you forgot this!
}

Calling your program with different values doesn't lead to a segfault, I've tried it with different numbers.

Another error: the main function should be defined as:

• int main(void);
• int main(int argc, char *argv[]);
• int main(int argc, char **argv);

You should change that. See What should main() return in C and C++?

For general information. If you want to exit a void function, all you have to do is use return; without any value, like this:

void foo(void)
{
    do_some_work();

    if(should_i_terminate)
        return;

    keep_doing_work();
}