Question

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; } 

Answer 1

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; }