Why does forking my process cause the file to be read infinitely

Question

I\'ve boiled down my entire program to a short main that replicates the issue, so forgive me for it not making any sense.

input.txt is a text file that has a couple

Answer 1

The exit() call closes all open file handles. After the fork, the child and parent have identical copies of the execution stack, including the FileHandle pointer. When the child exits, it closes the file and resets the pointer.

  int main(){
        freopen("input.txt", "r", stdin);
        char s[MAX];
        prompt(s);
        int i = 0;
        char* ret = fgets(s, MAX, stdin);
        while (ret != NULL) {
            //Commenting out this region fixes the issue
            int status;
            pid_t pid = fork();   // At this point both processes has a copy of the filehandle
            if (pid == 0) {
                exit(0);          // At this point the child closes the filehandle
            } else {
                waitpid(pid, &status, 0);
            }
            //End region
            printf("%s", s);
            ret = fgets(s, MAX, stdin);
        }
    }