Re: fflush() on readonly files

From: Radim Kolar (hsn_at_netmag.cz)
Date: 06/19/04

  • Next message: Andrey Chernov: "Re: fflush() on readonly files" 
    Date: Sat, 19 Jun 2004 11:56:43 +0200
To: freebsd-arch@freebsd.org

    > > > 3 - Correct some programs depending on this
    > > Are there any such programs?
    Today I have stepped on another example: advancecomp (in ports):
    Code for returning size of file: lib/fz.c
    542 /**
    543 * Get the size of the file.
    544 */
    545 long fzsize(adv_fz* f)
    546 {
    547 if (f->type == fz_file) {
    548 struct stat st;
    549 if (fflush(f->f) != 0) {
    550 return -1;
    551 }

    > The behavior of fflush() on a read-only stream is not defined by any
    > relevant standards. It is a no-op.
    Returning an error is not no-op. It is a failure.

    There are 2 cases:
    1) Program knows that he has r/o fd and calls fflush() on it.
    > In my experience, fflush() is only called on input streams when the Microsoft
    > behavior is expected.
    2) Program do not knows that he has r/o fd and calls fflush() as part of his normal operation. For example fflush()+fstat() pairs and fflush()+fclose() pairs.
    This programs expects that fflush() on r/o files do not fails.

    I am interested in solving case #2. I have no troubles with #1 programs; there are not a very common.

    > Bottom line: learn C, fix your code.
    There are other languages also. Major problem with this behavior lies in
    various Python scripts. When they calls fflush() on r/o fd, exception is thrown
    and aborts program. They often calls fflush before close in class which
    supports both r/o and r/w fd and there is no way to check type of passed
    descriptor.
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  • Next message: Andrey Chernov: "Re: fflush() on readonly files"