What should I do to modify my fork() in C to run well?

I dont understand why my code does not work.

This is my code. I don't know why I'm get an error segment. Could somebody explain the reason to me?

#include <iostream>
#include <string>
#include <sys/types.h>
#include <unistd.h>

int id_process;

void manager_signal () {
    kill (id_process, SIGKILL);
    kill (getppid(),SIGKILL);
}

int main () {
    id_process = fork ();
    if (id_process==-1) {
        perror("ERROR to create the fork");
    } else {
        if ( id_process != 0 ) {
            printf("Father´s ID is %d \n", getpid());   
            alarm(5);
            (void) signal (SIGALRM, manager_signal);
            sleep (20);
            printf ("Running to where the father can be\n");
            alarm (0);    
        } else {
            printf ("CHildren´s ID is %d \n", getpid ());
            for (;;) {
                printf ( "Children RUN FOREVER ^^");
                sleep (2);
            }
        }
    }
    return 0;
}

From stackoverflow

• Your question is a little difficult to understand since you don't really explain what the error is, but I do have one question which I'm sure will be pertinent.

  Why is the "father" process killing its child and its parent? Shouldn't it kill its child and itself (id_process and getpid() rather than getppid() which is the parent PID)?

  That appears to be the problem. When I run that under Cygwin, it kills off my shell (darned annoying). If I change it to kill (getpid(),SIGKILL);, it terminates okay after five seconds with the following output:

  $ vi qq.cpp ; g++ -o qq qq.cpp ; ./qq.exe
  Fathers ID is 6016
  Childrens ID is 4512
  Children RUN FOREVER ^^
  Children RUN FOREVER ^^
  Children RUN FOREVER ^^
  Children RUN FOREVER ^^
  Children RUN FOREVER ^^
  Killed
  

  This is with the program modified as follows:

  #include <iostream>
  #include <string>
  #include <sys/types.h>
  #include <unistd.h>
  
  int id_process;
  
  void manager_signal (int x) {
      kill (id_process, SIGKILL);
      kill (getpid(),SIGKILL);
  }
  
  int main () {
      id_process = fork ();
      if (id_process==-1) {
          perror("ERROR to create the fork");
      } else {
          if ( id_process != 0 ) {
              printf("Fathers ID is %d\n", getpid());
              alarm(5);
              (void) signal (SIGALRM, manager_signal);
              sleep (20);
              printf ("Running to where the father can be\n");
              alarm (0);
          } else {
              printf ("Childrens ID is %d\n", getpid ());
              for (;;) {
                  printf ( "Children RUN FOREVER ^^\n");
                  sleep (1);
              }
          }
      }
      return 0;
  }
  

  Jonathan Leffler : Run the faulty program as: sh -c "./testprog"; then your main shell isn't killed. Good spotting on the incorrect definition for manager_signal(); can you still do: void manager_signal(int) to indicate that the function takes an int (the signal number) but ignores it? It was a nice feature in C++ as I recall it, one that C would do well to adopt too.

• I don't think

      kill (id_process, SIGKILL);
  

  is required either. You're killing the same process in the next instruction.