CODEWITHSUNDEEP
cunixprocesspipefork
Shan
Shan

Reputation: 3057

pipe() from 1 parent to multiple child processes in separate c file

I have a program that creates multiple child processes using fork(). The program starts in main of parent.c. After forking, the parent calls excel to execute child.c. How exactly do I share a pipe between the two different programs. I know I would have to create a pipe in parent.c for each child process like this:

int myPipe[nChildren][2];
int i;

for (i = 0; i < nChildren; i++) {
    if (pipe(myPipe[i]) == -1) {
        perror("pipe error\n");
        exit(1);
    }
    close(pipe[i][0]); // parent does not need to read
}

But what do I need to do in child.c?

Upvotes: 0

Views: 2227

Answers (1)

DoxyLover
DoxyLover

Reputation: 3484

The child process needs to communicate the pipe FD to the execl'ed program. The easiest way is to use dup2 to move the pipe to FD 0 (stdin). For example:

pid = fork();
if (pid == 0) {
  // in child
  dup2(pipe[i][0], 0);
  execl(...);
}

Alternatively, you could use a command-line argument in child.c to accept the FD number of the pipe. for example:

pid = fork();
if (pid == 0) {
  // in child
  sprintf(pipenum, "%d", pipe[i][0]);
  execl("child", "child", pipenum, (char *) NULL);
}

The child program would need to use atoi or strtoul to convert argv[1] to an integer and then use that as the input FD.

Upvotes: 2

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