Execute programs out of C

Question

I´m trying to get some values displayed on an eInk-Display (via SPI). I already wrote the software to initialize the display and display the values passed as command-line arguments. The problem is, because of the eInk-technology it takes a few seconds for the display to have fully actualized, so the display-program is also running for this time.

The other ("Master"-) program collects the values and does other stuff. It has a main loop, which has to be cycled through at least 10x/second. So I want to start the displaying program from within the main loop and immediately continue with the loop.

When using system() or execl(), the Master-program either waits till the display program is finished or exits into the new process.

Is there a way to just start other programs out of other ones without any further connection between them? It should run on Linux. May fork() be a solution?

fork() + exec() is one way. system("your command &"); is another. — Klas Lindbäck
– Klas Lindbäck, Commented Mar 5, 2018 at 13:14
"t has a main loop, which has to be cycled through at least 10x/second" What kind of real-time requirement is that? If your main loop takes longer than 100ms to execute, you have some real serious problems. Now what you should be doing here, is to write a multi-threaded program. — Lundin
– Lundin, Commented Mar 5, 2018 at 13:57

Jean-François Fabre · Accepted Answer · 2018-03-05 13:19:19Z

quick and dirty way: use system with a background suffix (&)

char cmd[200];
sprintf("%190s &","your_command");
system(cmd);

note that it's not portable because it depends on the underlying shell. For windows you would do:

sprintf("start %190s","your_command");

The main drawback of the quick & dirty solution is that it's "fire & forget". If the program fails to execute properly, you'll still have a 0 return code as long as the shell could launch the process.

A portable method (also allowing to take care of the return code of the process) is slightly more complex, involving running a system call from a thread or a forked executable. The quick & dirty solution does a fork + exec of a shell command behind the scenes.

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