[C Language] wait() example

[C Language] wait() example

/*

Process wait() example:



Here's an example call to wait(): a program spawns two children, then waits for their completion and behaves differently according to which one is finished. Try to compile and execute it.

*/



#include <sys/types.h>

#include <sys/wait.h>

#include <stdio.h>

#include <stdlib.h>



int main(int argc, char *argv[])

{

    pid_t whichone, first, second;

    int howmany;

    int status;



    if (  (first=fork())==0 ) /* Parent spawns 1st child */

    {

        printf("Hiya, I am the first child, ""and my id is %d\n",getpid());

        sleep(20); /* Sleep 10 sec, then exit */

        exit(0);

    }

    else if (first == -1)

    {

        perror("1st fork: something went bananas\n");

        exit(1);

    }

    else if (  (second=fork())==0  ) /* Parent spawns 2nd child */

    {

        printf("Hiya, I am the second child, ""and my id is %d\n",getpid());

        sleep(15); /* Sleep 15 sec, then exit */

        exit(0);

    }

    else if (  second == -1  )

    {

            perror("2nd fork: something went bananas\n");

            exit(1);

    }



    printf(  "This is the parent\n"  );



    howmany=0;

    while (howmany < 3) /* Wait twice */

    {

            whichone=wait(&status); // This wait will wait for child process. When child process return, then keep going.

            howmany++;



        if (whichone==first)

            printf("First child exited ");

        else

            printf("Second child exited ");



        if ((status & 0xffff)==0)

            printf("correctly\n");

        else

            printf("uncorrectly\n");

    }



    return 0;

}

Reference :

• 
  Unix- Open Source Softwares