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Mail Archives: djgpp-workers/2013/07/19/20:17:35

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Date: Sat, 20 Jul 2013 02:18:32 +0200
From: Juan Manuel Guerrero <juan DOT guerrero AT gmx DOT de>
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To: djgpp-workers AT delorie DOT com
Subject: Re: Set _IOERR if the file stream has been opened in wrong mode.
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Reply-To: djgpp-workers AT delorie DOT com

Am 18.07.2013 06:59, schrieb DJ Delorie:
>> man pages.  IIRC, DJGPP libc is derived from BSD to avoid (L)GPL
>> implications of merely using the compilation suite, so BSD man pages
>> should be considered carefully, if not as authoritative.
> V1 was bsd-derived.  V2 was written from scratch using the ANSI and
> POSIX specs as references.
>
> I looked in the code and didn't see anything where we specifically set
> the error flag, other than read() failing.  So, it looks like this is
> a DOS thing - that file just isn't readable.
>
> But I couldn't find anything in the posix/ansi specs that said what
> conditions cause errors, just that if errors happen ferror() says so.

Only for the record:

File is empty.  Reading from file (stream) using either fread or fgets
        | fopen("foobar", "w") | ferror | feof
-------+----------------------+--------+------
cygwin |  reading from file   |  TRUE  | FALSE
-------+----------------------+--------+------
linux  |  reading from file   |  TRUE  | FALSE
-------+----------------------+--------+------
mingw  |  reading from file   |  TRUE  | FALSE
-------+----------------------+--------+------
pcbsd  |  reading from file   |  TRUE  | FALSE
-------+----------------------+--------+------
djgpp  |  reading from file   |  FALSE | FALSE


        | fopen("foobar", "r") | ferror | feof
-------+----------------------+--------+------
cygwin |  reading from file   |  FALSE | TRUE
-------+----------------------+--------+------
linux  |  reading from file   |  FALSE | TRUE
-------+----------------------+--------+------
mingw  |  reading from file   |  FALSE | TRUE
-------+----------------------+--------+------
pcbsd  |  reading from file   |  FALSE | TRUE
-------+----------------------+--------+------
djgpp  |  reading from file   |  FALSE | TRUE




File is empty.  Writing to file (stream) using either fwrite or fputs
        | fopen("foobar", "r") | ferror | feof
-------+----------------------+--------+------
cygwin |   writing to file   |  TRUE  | FALSE
-------+----------------------+--------+------
linux  |   writing to file   |  TRUE  | FALSE
-------+----------------------+--------+------
mingw  |   writing to file   |  TRUE  | FALSE
-------+----------------------+--------+------
pcbsd  |   writing to file   |  TRUE  | FALSE
-------+----------------------+--------+------
djgpp  |   writing to file   |  FALSE | FALSE


IMHO, with this evidence it can taken for granted that for the C programing
community that uses one of the above enumerated systems, this behavior no
longer is a bug but a feature no matter if mandated or not by a standard and
it is a matter of fact that some coders already exploit this feature in their
code.  (No offending intention here).  I do not have access to other posix or
bsd-like systems.  These are all checks I can do.

As can be seen djgpp sets _IOEOF were appropriate and this can be checked
using feof() but it does not set _IOERR under the conditions described in
previous mails.  Below there is a new small patch that fixes the issue as
suggested, this time in _filbuf for fread an fgets and in _flsbuf for
fwrite and fputs.

Concerning the patch, suggestions, objections, comments and improvements
are always welcome.

If I get no positive response or any response at all, I will not insiste in
this issue anymore and assume that it is prefered to keep the current behavior
of the library.


Regards,
Juan M. Guerrero



diff -aprNU3 djgpp.orig/src/docs/kb/wc204.txi djgpp/src/docs/kb/wc204.txi
--- djgpp.orig/src/docs/kb/wc204.txi    2013-03-23 11:54:58 +0000
+++ djgpp/src/docs/kb/wc204.txi    2013-07-20 00:11:48 +0000
@@ -1289,3 +1289,11 @@ members of @code{struct rlimit}.
  The @acronym{C99} macros @code{isfinite}, @code{isinf}, @code{isnan}, @code{isnormal}, @code{isgreater},
  @code{isgreaterequal}, @code{isless}, @code{islessequal}, @code{islessgreater} and @code{isunordered}
  were added to comply with the @acronym{C99} standard.
+
+@findex fread AT r{, and setting @code{_flag} to @code{_IOERR} if stream has been opened with wrong mode}
+@findex fwrite AT r{, and setting @code{_flag} to @code{_IOERR} if stream has been opened with wrong mode}
+@findex fgets AT r{, and setting @code{_flag} to @code{_IOERR} if stream has been opened with wrong mode}
+@findex fputs AT r{, and setting @code{_flag} to @code{_IOERR} if stream has been opened with wrong mode}
+@code{fread}, @code{fwrite}, @code{fgets} and @code{fputs} now check that the file stream has
+been opened in correct mode.  If it is the wrong mode the file stream @code{_flag} flag will
+be set to @code{_IOERR} before aborting the operation.
diff -aprNU3 djgpp.orig/src/libc/ansi/stdio/filbuf.c djgpp/src/libc/ansi/stdio/filbuf.c
--- djgpp.orig/src/libc/ansi/stdio/filbuf.c    2013-07-16 18:00:12 +0000
+++ djgpp/src/libc/ansi/stdio/filbuf.c    2013-07-20 00:01:26 +0000
@@ -37,7 +37,11 @@ _filbuf(FILE *f)
      f->_flag |= _IOREAD;

    if (!(f->_flag & _IOREAD))
+  {
+    f->_flag |= _IOERR;
      return EOF;
+  }
+
    if (f->_flag & (_IOSTRG | _IOEOF))
      return EOF;
    f->_flag &= ~_IOUNGETC;
diff -aprNU3 djgpp.orig/src/libc/ansi/stdio/flsbuf.c djgpp/src/libc/ansi/stdio/flsbuf.c
--- djgpp.orig/src/libc/ansi/stdio/flsbuf.c    2013-07-16 18:00:14 +0000
+++ djgpp/src/libc/ansi/stdio/flsbuf.c    2013-07-20 00:01:18 +0000
@@ -31,7 +31,10 @@ _flsbuf(int c, FILE *f)
    }

    if (!(f->_flag & _IOWRT))
+  {
+    f->_flag |= _IOERR;
      return EOF;
+  }

    /* No-op for full string buffers */
    if (f->_flag & _IOSTRG)

- Raw text -


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