ForkOn 20/01/2020 21:28, Anton Shepelev wrote:
> Keith Marshall to Anton Shepelev:
>
>>> On the other hand, this worked with GCC 4.*...
>>
>> GCC-4.x with what options?
>
> The same test case as posted, but with the GCC I had before
> the upgrade.
Well, I no longer have GCC-4 available, to check its behaviour, but the
__STRICT_ANSI__ restriction is, (and IIRC always has been), imposed
within the mingwrt headers, so any compiling option which activates the
__STRICT_ANSI__ feature test, (as any "-std=..." does), should decline
to support _fileno(), regardless of GCC version.
>> Eli is 100% correct -- -std=c++11 turns on strict ANSI,
>> (or more correctly ISO-C++), conformance checking, and
>> since fileno() is a POSIX.1 extension to ISO-C, (and
>> _fileno() is a Microsoft specific equivalent extension),
>> if you request strict ISO-C/ISO-C++ conformance checking,
>> then either will be rightfully rejected.
>
> Have you an idea why, then, fileno() is not rejected on
> Linux with -std=c++11?
One can only speculate that GLIBC headers are less rigorous in their
interpretation of __STRICT_ANSI__; opinions may differ on this, but in
mine, that's a defect in GLIBC.
> To be specific -- this program:
>
> #include <stdio.h>
>
> int main( void )
> { FILE *f;
> f = stdin;
> fileno( f );
> return 0;
> }
>
> compiles with -std=c++11? Is it due to a bug or the
> courtesy of developers?
See above. IMO, this is a GLIBC defect.
>>> May I link it in manually from the MinGW library in
>>> which it *is* implemented?
>>
>> Of course. You will get it from the default C-runtime
>> library, but you will need to explicitly declare it
>> yourself.
>
> I had already tried that:
>
> #include <stdio.h>
> int _fileno( FILE *stream );
> int main( void )
> { FILE *f;
> _fileno( f );
> return 0;
> }
>
> but the linker fails with:
>
> undefined reference to `_fileno(_iobuf*)'
Apologies. _fileno() is not implemented as a function, in Microsoft's
C-runtime library; it is defined as a macro in <stdio.h>, (or <cstdio>
for use in C++ code). The following works (tested on Manjaro-Linux,
with my own self-built MinGW cross-compiler, and run under Wine):
$ cat foo.cc
#include <cstdio>
#if defined __MINGW32__ && __STRICT_ANSI__
int _fileno( FILE * );
#define _fileno(__F) ((__F)->_file)
#endif
int main()
{
FILE *f = stderr;
int fd = _fileno( f );
printf( "File descriptor for stderr = %d\n", fd );
return 0;
}
$ mingw32-g++ --version
mingw32-g++ (MinGW.org Cross-GCC Build-20191117-1) 9.2.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE.
$ mingw32-g++ -std=c++11 foo.cc
$ ./a.exe
File descriptor for stderr = 2
--
Regards,
Keith.
Public key available from keys.gnupg.net
Key fingerprint: C19E C018 1547 DE50 E1D4 8F53 C0AD 36C6 347E 5A3F
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