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

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of nil-
> admirari at mailo.com
> Sent: Monday, May 23, 2022 5:36 PM
> To: ffmpeg-devel at ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH v2 1/2] avutil/wchar_filename,
> file_open: Support long file names on Windows
> 
> >> Not possible for stat precisely because of function and struct sharing
> a
> >> name.
> 
> > That's exactly what is said above and before :-)
> 
> My previous question was not answered, so I had to look up the answer
> myself.
> 
> > I'm actually wondering how does it even compile. All stat structs in
> code
> > become struct win32_stat, and all calls to stat become calls to
> win32_stat,
> > which in turn wraps _wstati64. But _wstati64 does not accept struct
> win32_stat*,
> > it accepts struct _stati64*. Content of these structs is probably
> identical, but
> > it should not matter: C is typed nominally, not structurally.
> 
> Turns out C actually has a concept of compatible types:
> https://en.cppreference.com/w/c/language/type.
> 
> The problems is:
> > they are both structure/union/enumeration types, and
> > - (c99) if one is declared with a tag, the other must also be declared
> with the same tag.
> > ...
> > If two declarations refer to the same object or function and do not use
> compatible types,
> > the behavior of the program is undefined.
> 
> Your structure does not have the same tag as the CRT's one.
> Are you sure you want to rely on undefined behaviour?
> 
> I haven't compiled your code, but the following simple example:
> 
> struct A { int a, b, c; };
> struct B { int a, b, c; };
> void printA(struct A *a);
> 
> struct B b = { 1, 2, 3 };
> printA(&b);
> 
> generates a
> 
> warning: passing argument 1 of ‘printA’ from incompatible pointer type [-
> Wincompatible-pointer-types]
>     |     printA(&b);
>     |            ^~
>     |            |
>     |            struct B *
> note: expected ‘struct A *’ but argument is of type ‘struct B *’
>     | void printA(struct A *a)
> 
> Are you sure you wanna add a couple of similar warnings to the project?

This is not what's happening. No warnings, not even from clang diagnostics
with -Weverything.


> Needless to repeat, _USE_32BIT_TIME_T is not supported.

I don't think it ever was. Have you been compiling and using ffmpeg 
successfully with this?

Kind regards,
sw