Popen problem, program freeze

This is a discussion on Popen problem, program freeze within the C Programming forums, part of the General Programming Boards category; I am writing code in C and I use popen in read mode so as to call an external application, ...

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    Popen problem, program freeze

    I am writing code in C and I use popen in read mode so as to call an external application, take its output and edit them.

    Here comes the problem. The output of this particular application are non-stop, that is to say it produces output continuously. The result is that by the time I call popen, the programme freeze. I can do neither pclose nor something else. Really, I am in serious problem since this output is of paramount importance for my application.

    I'm looking forward for your help, i'll really appreciate it.

    Thx in advance.
    Last edited by TuXaKoS; 04-28-2010 at 05:29 AM.

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    I'm not sure what you mean by "by the time I call popen, the programme freeze". popen is what starts the other application, right? I would be very surprised if you managed to lose information that way.

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    popen is into the main(). when the program reaches this command, it freezes. if i run ps -x i see the other application running. If i kill the other application, my program continues and the gui appears.

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    I would guess that just means that you're not dealing with the output correctly. pclose (for instance) is not going to force-quit the other program, merely wait for it to finish. If the other program is not going to finish, then that's a problem. If you've got the data you want, and you want the other program to stop, then you could send it a signal I suppose.

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    I Just want the other application run in the background. My program running and i geting the output of the background application. Is that possible? :/ And how?

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    Quote Originally Posted by TuXaKoS View Post
    I Just want the other application run in the background. My program running and i geting the output of the background application. Is that possible? :/ And how?
    If you want the other program to keep running and you to keep getting the output, then don't call pclose. You can continually call fgets/fscanf/whatever to read from the pipe, although those will block until output from the other program arrives.

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    The problem is that when i call popen the program freeze, no other command after this execute :/ Any idea why? maybe because the output stream is non-stop?

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    Running some tests showed that, at least on this system that I am typing on right now, buffering could be standing in your way. (I.e., the output is fully buffered, not line-buffered, so if you are relying on seeing things as soon as a \n happens, well, no. I printed out 101 short lines (each ending with \n) and didn't receive any of them until the other process closed.) That means that, if for instance, the first thing after a popen is a fgets, you may be waiting a while to see anything. You can change the buffering of a FILE* with setvbuf().

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    Thx my friend. Everything seems to work now setvbuf() was the solution, i changed the buffer from full to line buffer

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