Multiple child process creation with their own name as command line arguments

[namnam]

I am familiar with a concept of creating a child process with fork() and able to create multiple child processes with for loop but how do I create three child processes running another program for eg. ducktales.cpp, with a different string name ("Huey", "Dewey", "Louie") as a command line arguments?

[kbw]

You need an exec variant. First you fork, then the child runs exec.
http://pubs.opengroup.org/onlinepubs/009695399/functions/exec.html

[namnam]

Thank you for your reply. I looked at the manual, still did not understand how to use it. Could you give me an example of using execl() with fork() for the child process creation named as Huey and running on the ducktales.cpp? Thank you again.

[kbw]

This is an example of something that runs other programs in parallel and waits for them to complete.

// usage: run "prog arg args ..." "prog2 arg arg ..."
#include <unistd.h>
#include <sys/wait.h>
#include <sys/errno.h>

#include <string>
#include <vector>
#include <list>

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

typedef std::vector<std::string> prog_t;
typedef std::list<prog_t> progs_t;
typedef std::vector<pid_t> pids_t;

int wait(const pids_t& pids);
void run(pids_t& pids, const prog_t& prog);
prog_t split(const char* in);

int main(int argc, char* argv[])
{
	progs_t progs;
	std::for_each(argv + 1, argv + argc, [&](char *arg) { progs.push_back(split(arg)); });

	pids_t pids;
	for (auto& prog : progs) run(pids, prog);

	return wait(pids);
}

int wait(const pids_t& pids)
{
	int ret = 0;

	int stat;
	for (pid_t pid : pids) {
		waitpid(pid, &stat, 0);
		ret = ret || WEXITSTATUS(stat);
	}

	return ret;
}

void run(pids_t& pids, const prog_t& prog)
{
	int pid = fork();
	if (pid == 0) {
		// build arg vector
		std::vector<char*> args;
		for (const std::string& arg : prog) args.push_back(strdup(arg.c_str()));
		args.push_back(nullptr);

		execv(args[0], args.data()); // if exec works, this program instance ends here
		for (char* arg : args) free(arg);
		fprintf(stderr, "%s: execv failed: %s\n", args[0], strerror(errno));
	}
	else if (pid > 0)
		pids.push_back(pid);
}

prog_t split(const char* in)
{
	prog_t out;

	for (const char* begin = in;;) {
		const char* end = strchr(begin, ' ');
		if (!end) {
			if (*begin) out.emplace_back(begin); // append final string
			break;
		}

		out.emplace_back(begin, end);

		begin = end + 1;  // next entry
		while (isspace(*begin)) ++begin;  // skip spaces
	}

	return out;
}