Question

Assign tasks to child process using fork in C language

usage: ./a.out 1000, 3000 ...

The program does total of n tasks using fork. In each child process, it sums up from 0 to the current argument and then print out the result

for example, for argv[1]=1000, it sums up from 0 to 1000, then print out the result. then in another child process, it sums up 0 to 3000 then print out the result.

Pls write it in C language using fork

Answer 1

//Pls provide +ve rating

//since all local variable or global variables are not shared between child and parent , I am using shared memory to get the which number limit child has to execute its loop to find out sum.

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdlib.h>
#include<sys/wait.h>

int main(int argc,char **argv)
{
int pid,i;
int no_children,parent_id,sum=0,n;
//used shared memory to check on value of j
int *j;
int shmid = shmget(1000,1024,0666|IPC_CREAT);
j = (int*) shmat(shmid,(void*)0,0);
*j=1;
parent_id=getpid();
if(argc < 2)
{
printf("Usage: %s integer1 integer2 ... integern\n",argv[0]);
return -1;
}
//argv[0] is for program name, total number of chilren to be created is argc-1
no_children=argc-1;
//create n number of no_children
for(i = 0; i < no_children; i++)
{
pid=fork();
if(pid==0 && getppid() == parent_id) //child process
{
n=atoi(argv[*j]);
for(i = 0; i < n; i++)
{
sum+=i;
}
++(*j);
printf("Child of parent %d with pid %d of and sum from 0 to %d is %d\n",getppid(),getpid(),n,sum);
exit(0);
}
else if(getpid() == parent_id) //parent process
{
//printf("Parent process with pid %d waiting for it's chil(dren) to finish their job\n",getpid());
wait(0);
}
}
//detach shared memory
  
shmdt(j);
  
// delete shared memory
shmctl(shmid,IPC_RMID,NULL);
return 0;
}

========================

program run without arg

./a.out

//output1

Usage: /home/a.out integer1 integer2 ... integern

======================

//rpogram run with

./a.out 1000 3000

//output2

Child of parent 5 with pid  6 of and sum  from 0 to 1000 is 499500                                                                   

Child of parent 5 with pid  7 of and sum from 0 to 3000 is 4498500  

=======================

//program run with 4 numbers

./a.out 1000 3000 2500 2000

//output3

Child of parent 5 with pid 6 of and sum from 0 to 1000 is 499500   
Child of parent 5 with pid 7 of and sum from 0 to 3000 is 4498500
Child of parent 5 with pid 8 of and sum from 0 to 2500 is 3123750
Child of parent 5 with pid 9 of and sum from 0 to 2000 is 1999000

====================

//rpogram run with 5 args

./a.out 1000 3000 2500 2000 20

//output4

Child of parent 5 with pid  6 of and sum from 0 to 1000 is 499500                                                                   

Child of parent 5 with pid  7 of and sum from 0 to 3000 is 4498500                                                                  

Child of parent 5 with pid  8 of and sum from 0 to 2500 is 3123750                                                                  

Child of parent 5 with pid  9 of and sum from 0 to 2000 is 1999000                                                                  

Child of parent 5 with pid  10 of and sum from 0 to 20 is 190