Signal handling

This is a discussion on Signal handling within the C Programming forums, part of the General Programming Boards category; Hello again! Unfortunately I encountered problems after finding my function. What I want to do is to handle the situation ...

  1. #1
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    Signal handling

    Hello again!

    Unfortunately I encountered problems after finding my function.

    What I want to do is to handle the situation where the user tries to end the program by "Ctrl-C" so a temp-file is erased before exiting the program.

    I found the function signal(), but I'm not sure how to use it. It seems that you can set it to do some default action when you receive a Ctrl-C for example, but how do I handle it? Can I get it to call a different function for example?

    That is if I set a global boolean to true when I have created the tempfile, but before I am done with what I want to do I can erase the tempfile before exiting? (And how would I do that?)

  2. #2
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    Sorry, the function was sighandler (it has to work in Unix aswell as Linux)

  3. #3
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    Yes, you make a signal handler for SIGINT which is the signal sent when you press CTRL-C (nominally, technically it is possible to change that into some other key, but very rarely done in real life)

    I wouldn't make a flag, I would just delete any file(s) that you want to have deleted. If the file isn't there, you don't cause any problem by trying to delete a file that doesn't exist. And it makes the code simpler. It's not like it's your "normal path of execution", so the fact that it is a tiny bit slower than testing a flag and deleting a file only when the flag is set is pretty much irelevant.

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    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Mats is right. I have found that the best use for signals is when you need a program to behave in a specific way without human intervention, such as forcing a timeout. The setup is somewhat complicated.

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    if u want 2 call a function on recieving a signal ..

    first send the signal using kill()

    catch the signal in the desired process using signal() which takes the SIGNAL u want 2 send and d signal handler as arguments.

    now define this signalhandler func in ur program and thr call any function u want 2 ..
    jus like dat http://www.ecst.csuchico.edu/~beej/g...c/signals.html

  6. #6
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    Thank you!

    The example on that page was great. It does exactly what I wanted in my program so I'll use that.

    The reason I want to use a boolean is that the tempfile is used to store information from an "original" which I will remove some information from. The program gets information from a user about systems in use. This is stored in a file called .active. When a user wants to remove a system from that list I copy the original file to .tmp, and then I copy all the systems back to .active except the one to remove. After that it removes the .tmp file.

    But the other day I started the program in "remove"-mode, and pressed "Ctrl-C", and when I ran it again it didn't run because the .tmp-file already existed (I don't want to accidentally remove a .tmp-file not created by my program so I check if it exists), so if the user presses Ctrl-C I want to restore the .active-file and remove the .tmp-file before exiting. So that's why I want the boolean (or some other parameter), to know if the .tmp-file has been created before the user has pressed Ctrl-C.

    Thanks again for the help. This is a great forum. A lot of talented programmers here :-)

  7. #7
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    I don't know if it would have been an acceptable solution for you in this case, but there's the tmpfile function declared in stdio.h with can be used if you only need a temporary file. It's supossed to get deleted when the program terminates normally. However, I'm not sure if the file created by tmpfile is deleted is the program is interrupted by a SIGINT signal, since I have some doubt this is considered as a "normal termination".
    I hate real numbers.

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