C create many child process using exec and pipe [closed] - c

Question

Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 7 years ago.
Improve this question
I want to create as many child processes as the user sends in the argument. And I succeeded. However, I have to create child processes using the exec function, I do not know how to do it. Childs process are to be created as separate programs and run
by exec. In addition, I would like every child process to communicate with the main process (parent) using pipe. I do not know how to do it. So far I managed to write something like this:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
int main(int argc, char **argv)
{
pid_t pid;
if(argc < 3)
{
printf("Not enought arguments");
exit(0);
}
int number = atoi(argv[2]); // number of childern
pid_t pids[number],pid_s;
int i,n=number,status;
int pipes[number*2];
char buff[512];
if(strcmp("-p", argv[1]) == 0)
{
//
}
if(strcmp("-f", argv[1]) == 0)
{
//
}
switch (pid = fork()) {
case -1:
perror("Error in fork");
exit(0);
break;
case 0:
for(i=0; i < n; i++)
{
if((pids[i] = fork()) < 0)
{
perror("error fork");
}
else if(pids[i] == 0)
{
close(pipes[0]);
char *reply = "message";
write(pipes[1], reply, strlen(reply)+1);
execvp(argv[0],NULL);
}
}
while(n > 0)
{
pid_s = wait(&status);
--n;
}
break;
default:
close(pipes[1]);
read(pipes[0],buff,80);
printf("Message: %s", buff);
if(wait(0) == -1)
{
}
break;
}
return 0;
}
I correct the code, the child creates a new process by the exec. I would like to the child communicated with the main process by pipe. Do it in a loop best?

Answer 1

this example code, snipped from: http://www.cs.ecu.edu/karl/4630/sum01/example1.html shows how to use the execvp() function, with minor modifications by me.
It uses function parsecmd(cmd,argv), which is not writtten here, but which breaks cmd at spaces and stores the pieces into (local array) argv[], followed by a null pointer. For example, parsecmd("eat the banana", argv) will set argv as follows.
argv[0] = "eat"
argv[1] = "the"
argv[2] = "banana"
argv[3] = NULL
This example also presumes that there might be other child processes running in background, and that they might terminate while the shell is waiting for the current command to stop. A function called process_terminated is use to handle the termination of a background process. It is not written here.
int runcmd(char *cmd)
{
char* argv[MAX_ARGS];
pid_t child_pid;
int child_status;
parsecmd(cmd,argv);
child_pid = fork();
if(child_pid == 0) {
/* This is done by the child process. */
execvp(argv[0], argv);
/* If execvp returns, it must have failed. */
fprintf( stderr, "execvp failed due to %s\n", strerror(errno) );
exit(0);
}
else {
/* This is run by the parent. Wait for the child
to terminate. */
do {
pid_t tpid = wait(&child_status);
if(tpid != child_pid) process_terminated(tpid);
} while(tpid != child_pid);
return child_status;
}
}