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To: cs551@merlot.usc.edu
Subject: Re: CS551 Final2 - disk quota
Date: Wed, 19 Nov 2008 08:15:05 -0800
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > Do we have to check disk space for saving files in permanent space?
  > If so, what system call should we use?

You generally cannot find out how much disk space is
available to you.  So, you must do the following.  When you
write to the file, you must check return code.  When you
close the file, you must check return code.  If something
failed, you must delete the file and tell the user that there
is no space (so that the user can create space by removing
files).

You don't need to change your code much to get this done.
If your original code (without error checking) is:

    while (writing_to_file) {
        fwrite(N bytes to file);
    }
    fclose(...);

All you need is to change it to the following:

    boolean something_wrong=false;

    while (writing_to_file) {
        if (fwrite(N bytes to file) != N) {
            something_wrong = true;
        }
    }
    if (fclose() == EOF) {
        something_wrong = true;
    }
    if (something_wrong) {
       print error message to user
       unlink(the_file_you_were_writing_to);
    }
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>