[FFmpeg-devel] compound literal in public header file

[Tomas Härdin]

ons 2018-05-16 klockan 11:16 +0200 skrev Tobias Rapp:
> On 16.05.2018 10:29, Tomas Härdin wrote:
> > ons 2018-05-16 klockan 10:18 +0800 skrev Zhao Zhili:
> > > The av_err2str macro in libavutil/error.h use compound literal:
> > > 
> > > #define av_err2str(errnum) \
> > >       av_make_error_string((char[AV_ERROR_MAX_STRING_SIZE]){0},
> > > AV_ERROR_MAX_STRING_SIZE, errnum)
> > > 
> > > C++ compiler may not support it or treat the usage as invalid.
> > > For example, g++ 5.4 raise an error: taking address of temporary
> > > array.
> > > 
> > > 1. Should the macro be defined for C only?
> > > 2. Or make it as valid C++? (I don't know how to do that)
> > 
> > First of all, this shouldn't matter since av_err2str is not actually
> > used in any header. libavutil/timer.h makes use of it in another macro,
> > so that also doesn't matter.
> > 
> > Second, libavutil is a C library, not a C++ library. However, it might
> > be nicer to make that a static inline function, if possible. Or move it
> > to an internal header, since it doesn't look like something that should
> > be exposed as part of the public API.
> 
> ffmpeg.c/ffprobe.c is using it for assembling log messages and I'm using 
> it in my private tools, too. As it is a convenient utility function I 
> would prefer to keep it in the public headers of libavutil.

ffmpeg.c/ffprobe.c are C.. :)

If you're in C++, why don't you just write your own variant that
returns std::string?

/Tomas