Error sending signal to child process in C

Question

I tried to find out if this is possible, how I did it or not. This program must fork the child process that prints to STDOUT, and the parent must exit to return a terminal request. Then the child must wait for SIGINT to tell when to close. However, I remember reading that SIGINT only sends processes in the foreground, which explains why CTRL + C does not affect my abandoned child. Is there a way to force an abandoned child to receive a signal sent from the terminal, or some system call in the terminal to bring him to the forefront, where can he get a SIGINT? Or is my search hopeless?

the code:

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

/* signal handler for the child process */
void catchInt (int signum)
{
 printf("\nMy sincerest apologies, master\n");
    exit(0);
}

/* signal handler for the parent process */
void ignoreInt (int signum)
{
 /* prevent any extra output from being printed */
 fflush(stdout); 
 /* wait for child to apologize before replying */
 wait(NULL);
 printf("You're welcome\n");
 exit(0);
}

/* signal handler for the child alarm */
void catchAlarm (int signum)
{
 printf("It great to be alive\n");
 /* reset the alarm */
 signal(SIGALRM, catchAlarm);
 alarm(3);
}

int main () {

 pid_t  pid;

 /* fork process */
 pid = fork();
 if (pid < 0) /* error handler */ 
 {   
  fprintf(stderr, "Fork Failed");
  exit(-1);
 }

 /* child */
 else if (pid == 0) 
 { 
  printf("It great to be alive\n");
  /* catch SIGINT and handle as the child should */
  signal(SIGINT, catchInt);
  /* catch SIGALRM being sent by alarm() */
  signal(SIGALRM, catchAlarm);
  /* set alarm for 3 seconds */
  alarm(3);
  for ( ;; )
  {
   printf("I have 42001 children and not one comes to visit\n");
   usleep(500000);
  }   
 }

 /* parent */
 else 
 {
  /* exit to abandon child process in the background */
  exit(0);
 }

 return(0);
}

Answer 1

, SIGINT, , . :

int ctty = open("/dev/tty", O_RDONLY);
while (tcgetpgrp(ctty) == getpgrp())
    usleep(100000);
setpgid(0, tcgetpgrp(ctty));
close(ctty);

( , , , , , , . ..)

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PS: , - , . , , , , , .

Answer 2

kill :

kill -2 12345

, , , PID ( PID ). (, ignoreInt() PID ), , , - kill .

:

#include  <stdio.h>
#include  <unistd.h>
#include  <stdlib.h>
#include  <signal.h>

static void catchInt(int signum)
{
    printf("\nMy sincerest apologies, master (%d)\n", signum);
    exit(0);
}

static void catchAlarm(int signum)
{
    printf("It great to be alive (%d)\n", signum);
    signal(SIGALRM, catchAlarm);
    alarm(3);
}

int main(void)
{
    pid_t  pid = fork();

    if (pid < 0)
    {   
        fprintf(stderr, "Fork Failed");
        exit(-1);
    }
    else if (pid == 0) 
    { 
        printf("It great to be alive (%d)\n", (int)getpid());
        signal(SIGINT, catchInt);
        signal(SIGALRM, catchAlarm);
        alarm(3);
        for ( ;; )
        {
            printf("I have 42001 children and not one comes to visit\n");
            usleep(500000);
        }   
    }
    return(0);
}

<sys/types.h>, , , POSIX (, , <unistd.h>). , , , , , , , , . (OTOH, wait(), <sys/wait.h> , , <sys/types.h> .)

Answer 3

, SIGINT , CTRL C ( stty intr).

You can always send SIGINT to a specific process with kill -INT 99999(where 99999is the process identifier).