How to start a executable within a C++ program and get its process id (in linux)? [closed]

Question

i tried system(), but somehow when the secondary program runs, my main program(primary program which executes the secondary) hangs

and second issue is how do i obtain the process id of the secondary program in my main program?

Answer 1

In the parent process you want to fork.

Fork creates an entirely new process and returns either the child process's pid to the calling process, and 0 to the new child process.

In the child process you can then use something like execl to execute your desired secondary program. In the parent process you can use waitpid to wait for the child to complete.

Here is a simple illustrative example:

#include <iostream>
#include <sys/wait.h>
#include <unistd.h>
#include <cstdio>
#include <cstdlib>

int main()
{
    std::string cmd = "/bin/ls"; // secondary program you want to run

    pid_t pid = fork(); // create child process
    int status;

    switch (pid)
    {
    case -1: // error
        perror("fork");
        exit(1);

    case 0: // child process
        execl(cmd.c_str(), 0, 0); // run the command
        perror("execl"); // execl doesn't return unless there is a problem
        exit(1);

    default: // parent process, pid now contains the child pid
        while (-1 == waitpid(pid, &status, 0)); // wait for child to complete
        if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
        {
            // handle error
            std::cerr << "process " << cmd << " (pid=" << pid << ") failed" << std::endl;
        }
        break;
    }
    return 0;
}

Answer 2

Use fork to create a new process, then exec to run a program in the new process. There are many such examples.