bug in freopen

Schwarz, Konrad konrad.schwarz@siemens.com
Fri Jul 15 07:32:00 GMT 2005

> -----Original Message-----
> From: newlib-owner@sources.redhat.com 
> [mailto:newlib-owner@sources.redhat.com] On Behalf Of Eric Blake
> Sent: Friday, July 15, 2005 1:14 AM
> To: cygwin@cygwin.com; newlib@sourceware.org
> Subject: bug in freopen
> POSIX requires that freopen(NULL, mode, f) reopen f in the 
> new mode, and allows implementations the option of not even 
> closing f in the first place.  But in cygwin, it is failing 
> with EFAULT, which is not even one of the errors allowed by POSIX.
> http://www.opengroup.org/susv3xsh/freopen.html

Just to be pedantic: POSIX allows system interfaces to set <errno> to
values additional to those documented in the standard, so this in itself
is not necessarily a bug.

Of course, freopen() should not be calling open() with NULL, it appears
this case has not been implemented in newlib. 

> #include <stdio.h>
> #include <errno.h>
> int main(void)
> {
>    FILE* f = freopen (NULL, "rb", stdin); /* Ensure that 
> stdin is binary */
>    printf ("file is %s, errno %d:%s\n", f ? "good" : "null", errno,
>            strerror(errno));
>    return 0;
> }
> CVS coreutils recently switched to this idiom, replacing its 
> former use of the nonstandard <io.h> and setmode() with 
> something that is required by the standards.  But until this 
> bug is fixed, CVS coreutils will not work with cygwin.  The 
> strace in cygwin shows that newlib tried to perform 
> open(NULL), which is the cause of the EFAULT.
> --
> Eric Blake

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