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I don't want to use system() in my C program, because system(3) blocks and this is not what I want. What is the optimal way to do it?

cateof
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  • Does this answer your question? [Non-blocking version of system()](https://stackoverflow.com/questions/1002513/non-blocking-version-of-system) – Maxpm Jan 10 '21 at 04:40

5 Answers5

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I think that a quick and dirty action is to call sytem(command &). the & will spawn the new process.

cateof
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  • Absolutely +1. `system()` is platform-dependent anyway. Instead of making a mess of your source with `fork()` or stuff like that, use the shell that `system()` gives you access to. – DevSolar Oct 01 '10 at 11:25
  • great solution much better than fork if you aks me – Martin Meeser Jan 13 '15 at 15:05
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Use fork() to create a new process and then use system() (or any exec function) in it. The original process will then be able to continue executing.

abyx
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8

The answer depends on what your real goal is. You don't say what platform you're on, and I know very little about Windows, so this only covers your options on linux/unix.

  1. You just want to spawn another program, and don't need to interact with it. In this case, call fork(), and then in the child process run execve() (or related function).

  2. You want to interact with another program. In this case, use popen().

  3. You want part of your program to run as a subprocess. In this case, use fork(), and call whatever functions you need to run in the child.

  4. You need to interact with part of your program running as a subprocess. Call pipe() so you have a file descriptor to communicate through, then call fork() and use the file descriptor pair to communicate. Alternatively, you could communicate through a socket, message queue, shared memory, etc.

bstpierre
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  • Nice rundown of the options at hand, and how to choose between them. – Matt Joiner Oct 01 '10 at 16:01
  • `fork()` then `system()` will leave a useless process hanging around for the shell to finish. It is better to call `execve()` or similar in the child process instead of `system()`. If you want to use the shell's features, then exec `/bin/sh`. – jilles Oct 02 '10 at 13:39
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You might want to use popen. It creates new processes and allows you to redirect the process output to your own process.

Didier Trosset
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If in windows, use the ShellExecute() function from the Windows API.

If in Unix, go for fork() then system() as mentioned.

Ruel
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