Do other tasks while a system() command is being executed

Question

I have this c++ program that is doing a simple ping on a specified ip address. I am not into networking so i'm just using the system() command in c++ to execute the ping from a shell and store the results in a file, that's easy.

The problem is that i want some dots to be printed on the screen while the system() command is being executed. i tried with:

while(system(cmd))
{ 
//execute the task here
}

but no success. I think that i should create threads or something.

Can you help me ? What exactly i am supposed to do in order to get this done as i want to ?

Answer 1

The problem with system is that it suspends execution until completion. On unix systems you will need to use a sequence of fork, execv, dup2 and pipe. This will allow you to do something more useful. See http://docs.linux.cz/programming/c/unix_examples/execill.html for an example.

Answer 2

If you are on a unix system, you can start a command with an & to indicate that it runs in the background like this: myscript &

This will start a new process separate from the current program. You need to pick up the process number (hopefully from system, my c posix api knowledge is rusty) and then check up on it probably with a call to something like wait or waitpid with non-blocking turned on.

This is complicated for a beginner -- I'll let someone else post details if still interested.

Answer 3

Edit On consideration, I believe that popen is the way to go with or without output from cmd.

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Older

You are probably looking for something in the wait (2) family of commands plus a fork and exec.

From the manual page

The wait() function suspends execution of its calling process until stat_loc information is available for a terminated child process, or a signal is received. On return from a successful wait() call, the stat_loc area contains termination information about the process that exited as defined below.

Or if cmd returns some progress information you want popen (3) which is discussed in a number of existing SO questions; for instance How can I run an external program from C and parse its output?.