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problem with mutltiple fork()

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# 1  
Old 03-07-2012
problem with mutltiple fork()
Hi, can someone please help me with creating mutltiple fork.. I was expecting something like this:

I am a child: 1 PID: 1215
I am a child: 2 PID: 1216
I am a child: 3 PID: 1217
I am a child: 4 PID: 1218
I am a child: 5 PID: 1219
I am a child: 6 PID: 1215
I am a child: 7 PID: 1216
I am a child: 8 PID: 1217
I am a child: 9 PID: 1218
I am a child: 10 PID: 1219
I am a child: 11 PID: 1215
I am a child: 12 PID: 1216
I am a child: 13 PID: 1217
I am a child: 14 PID: 1218
I am a child: 15 PID: 1219
I am a child: 16 PID: 1215
I am a child: 17 PID: 1216
I am a child: 18 PID: 1217
I am a child: 19 PID: 1218
I am a child: 20 PID: 1219

but i get this on output:

I am a child: 1 PID: 1950
I am a child: 2 PID: 1951
I am a child: 3 PID: 1952
I am a child: 4 PID: 1953
I am a child: 5 PID: 1954
I am a child: 6 PID: 1955
I am a child: 7 PID: 1956
I am a child: 8 PID: 1957
I am a child: 9 PID: 1958
I am a child: 10 PID: 1959
I am a child: 11 PID: 1960
I am a child: 12 PID: 1961
I am a child: 13 PID: 1962
I am a child: 14 PID: 1963
I am a child: 15 PID: 1964
ladislav@ubuntu:~$ I am a child: 16 PID: 1965
I am a child: 17 PID: 1966
I am a child: 20 PID: 1969
I am a child: 18 PID: 1967
I am a child: 19 PID: 1968


Here is my source code. Thank you for your help in advance.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void Fork_Children (int N_Children)
{
    int i;
    int pid;
    for (i = 1; i <= N_Children; i++) 
    {
        pid = fork();
       
        if (pid == 0) 
        {
            printf("I am a child: %d PID: %d\n",i, getpid());
            sleep(5);            
            return;
        }
    }
}

int main (int argc, char *argv[]) 
{
    Fork_Children(atoi(argv[1]));
    return 0;
}

# 2  
Old 03-07-2012
Your main() program doesn't wait for its children, so finishes first, and you get a shell prompt before the children even finish sleeping.

To wait for child processes, do wait().

Code:
for(n=1; n<atoi(argv[1]); n++)
{
  int s;
  wait(&2);
}

# 3  
Old 03-07-2012
you men something like this:
because it didn't work.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>


int main (int argc, char *argv[])
{
    int i;
    int pid;
    for (i = 1; i <= atoi(argv[1]); i++) 
    {
        pid = fork();
        wait(&2); 
        if (pid == 0) 
        {
            printf("I am a child: %d PID: %d\n",i, getpid());
                   
            return 0;
        }
    }
}

# 4  
Old 03-07-2012
I meant the code I actually gave you, right at the end of main(), after your function but before the return 0. I don't know where you got wait(&2). It takes a pointer to a variable.
# 5  
Old 03-07-2012
I have solved it with wait(NULL). But now I have no idea how to put pipes into it. I mean the first child generate for example random number and send it via pipe to another children and to the last child. I was thinking about to use 2d array pipe (int pipe[Number_of_children][2]), but I don't know how to put it into the for loop..
Code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int main (int argc, char *argv[])
{
int i;
int pid;
for (i = 1; i <= atoi(argv[1]); i++) 
{
pid = fork();
wait(NULL);
if (pid == 0) 
{	

printf("I am a child: %d PID: %d\n",i, getpid());

return 0;
}
}
}

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