On Wed, Aug 31, 2011 at 10:49 AM, Bruno Haible <br...@clisp.org> wrote:
> Claudio Bley wrote:
>> Furthermore, using NULL as filename does not work at all using the MS
>> C runtime library (debug assertion violation).
>>
>> --------------------
>> --- freopen.c.1 2011-08-25 21:05:34 +0200
>> +++ freopen.c 2011-08-25 21:08:52 +0200
>> @@ -38,6 +38,9 @@
>> rpl_freopen (const char *filename, const char *mode, FILE *stream)
>> {
>> #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
>> +# ifdef _MSC_VER
>> + if (!filename) return NULL; /* would trigger a runtime error on MSVC */
>> +# endif
>> if (filename && strcmp (filename, "/dev/null") == 0)
>> filename = "NUL";
>> #endif
>>
>> --------------------
>
> Unfortunately, freopen (NULL, ...) is not something gnulib can support
> portably. POSIX:2008 specifies the effects of this call in
> <http://pubs.opengroup.org/onlinepubs/9699919799/functions/freopen.html>:
>
> If filename is a null pointer, the freopen() function shall attempt to
> change the mode of the stream to that specified by mode, as if the name
> of the file currently associated with the stream had been used. In this
> case, the file descriptor associated with the stream need not be closed
> if the call to freopen() succeeds. It is implementation-defined which
> changes of mode are permitted (if any), and under what circumstances.
>
> For testing, I added this line to the freopen test:
>
> *** tests/test-freopen.c.orig Wed Aug 31 10:30:38 2011
> --- tests/test-freopen.c Wed Aug 31 10:25:43 2011
> ***************
> *** 29,34 ****
> --- 29,35 ----
> main ()
> {
> ASSERT (freopen ("/dev/null", "r", stdin) != NULL);
> + ASSERT (freopen (NULL, "r", freopen ("/dev/null", "rw", stdin)) != NULL);
>
> return 0;
> }
>
> The result is that it fails on several platforms
> (OpenBSD 4.9, AIX 7.1, HP-UX 11.23, IRIX 6.5, OSF/1 5.1, Solaris 10, mingw):
> test-freopen.c:32: assertion failed
> FAIL: test-freopen
>
> And implementing this requires a conversion from file descriptor to filename
> (at least, that's what the glibc implementation of freopen (NULL, ...) uses),
> which is only available on very few operating systems.
Time to abstract this functionnality ?
I agree with portability goal but under windows we have the name using
FileInformation of GetFileInformationByHandleEx
Bastien
