ROS commands from c++ applications

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Hi

I am fairly new to ROS. I am trying to run the ROS commands like roscore, rosrun and so on from external c++ applications. I am able to run roscore command but when I try to run multiple commands like, roscore then rosrun then other commands it doesn't work. So, is it possible to achieve this?

For example:

working code:

char* argsUwsim[5] = {"bash", "-i", "-c", "/opt/ros/kinetic/bin/roscore", NULL};
execvp(argsUwsim[0], argsUwsim);

Not working code:

char* argsUwsim[5] = {"bash", "-i", "-c", "/opt/ros/kinetic/bin/roscore", NULL};
char* argsUwsimSecond[5] = {"bash", "-i", "-c", "/opt/ros/kinetic/bin/rosrun uwsim uwsim", NULL};
execvp(argsUwsimSecond[0], argsUwsimSecond);

"not working code" only starts the roscore and then do nothing. I have tried to use c++ fork() method to create child process for running multiple commands but it still doesn't work or I am not running it right.

here is the code with fork():

char* argsMaster[5] = {"bash", "-i", "-c", "/opt/ros/kinetic/bin/roscore", NULL};
char* argsUwsim[5] = {"bash", "-i", "-c", "/opt/ros/kinetic/bin/rosrun uwsim uwsim", NULL};

pid_t pid = fork();

    if(pid == 0){
        execvp(argsUwsim[0], argsUwsim);

    } else if(pid > 0){
        execvp(argsMaster[0], argsMaster);

    }

here, the roscore starts and stays there, nothing happens for the rosrun command. If I stop the roscore with ctrl + c ,whole program stops.