Non-blocking version of system()

Question

I want to launch a process from within my c program, but I don't want to wait for that program to finish. I can launch that process OK using system() but that always waits. Does anyone know of a 'non-blocking' version that will return as soon as the process has been started?

[Edit - Additional Requirement] When the original process has finished executing, the child process needs to keep on running.

Answer 1

Why not use fork() and exec(), and simply don't call waitpid()?

For example, you could do the following:

// ... your app code goes here ...
pid = fork();
if( pid < 0 )
    // error out here!
if( !pid && execvp( /* process name, args, etc. */ )
    // error in the child proc here!
// ...parent execution continues here...

Answer 2

One option is in your system call, do this:

 system("ls -l &");

the & at the end of the command line arguments forks the task you've launched.

Answer 3

The normal way to do it, and in fact you shouldn't really use system() anymore is popen.
This also allows you to read or write from the spawned process's stdin/out

edit: See popen2() if you need to read and write - thansk quinmars

Answer 4

In the end, this code appears to work. Bit of a mis-mash of the above answers:

pid = fork();

if (!pid)
{
    system("command here &");
}

exit(0);

Not quite sure why it works, but it does what I'm after, thanks to everyone for your help

Answer 5

You could use posix_spawnp() function. It's much similar to system() than the fork and exec* combination, but non-blocking.