Re: [FFmpeg-devel] [PATCH v2 1/2] avutil/wchar_filename, file_open: Support long file names on Windows

[Soft Works <softworkz@hotmail.com>]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Soft
> Works
> Sent: Tuesday, May 17, 2022 5:28 PM
> To: FFmpeg development discussions and patches <ffmpeg-
> devel@ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH v2 1/2] avutil/wchar_filename,
> file_open: Support long file names on Windows
> 
> 
> 
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> nil-
> > admirari@mailo.com
> > Sent: Tuesday, May 17, 2022 5:07 PM
> > To: ffmpeg-devel@ffmpeg.org
> > Subject: Re: [FFmpeg-devel] [PATCH v2 1/2] avutil/wchar_filename,
> > file_open: Support long file names on Windows
> >
> > > stat wasn't already defined as win32_stat.
> > > win32_stat was already defined but not mapped. That's what my
> change
> > > does.
> >
> > There are two defines in os_support.h:
> >
> > #  ifdef stat
> > #   undef stat
> > #  endif
> > #  define stat _stati64
> >
> > and
> >
> > DEF_FS_FUNCTION2(stat, _wstati64, _stati64, struct stat*)
> >
> > which defines win32_stat (not stat). This function takes struct
> stat*,
> > which due to previous define
> > expands into struct _stati64*.
> >
> > _stati64 and _wstati64 both take struct _stati64*, which is named
> > identically to the first function.
> > struct _stati64 expands into different structs depending on the
> value
> > of _USE_32BIT_TIME_T,
> > which your explicit structure definition does not capture, see:
> > https://docs.microsoft.com/en-us/cpp/c-runtime-
> library/reference/stat-
> > functions?view=msvc-170.
> > If someone defines_USE_32BIT_TIME_T, your code will fail to compile.
> 
> Yes, that's true. But there are hundreds of other things someone could
> define which makes compilation fail.
> We don't need to accommodate for every single possibility, and it's
> not
> that _USE_32BIT_TIME_T would be required or the default for 32bit
> compilation.
> 
> 
> > C allows functions and structs to have identical names, preprocessor
> > does not;
> > therefore win32_stat must be used explicitly where stat is required
> as
> > in file.c:160
> 
> Except when you define a compatible struct with the same name as the
> function - like I did.

I don't want to say that I'd consider this to be a great solution.
But the problem is that the function and struct names are identical
and when we want to re-define/map the function, we also need to
provide a struct of that name because the macro-replacement can't
work selectively.

Maybe there is some cool trick to handle this, yet I haven't had
a better idea so far.

Thanks,
softworkz


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