fails to handle __declspec(dllimport) properly

[mbechard]

When trying to compile ffmpeg with --enable-shared, the conversion fails.

This can be traced to this define
define av_export __declspec(dllimport)

And for example in libavformat/asfenc.c

It fails due to this line getting included from riff.h
extern av_export const AVCodecTag ff_codec_bmp_tags[];

Which creates in the converted c89 file for asfenc.c
extern __declspec(dllimport) const AVCodecTag ff_codec_bmp_tags[];

causing this line to have a compile error (in asfenc.c)
static const AVCodecTag * const tmp__1[] = {
codec_asf_bmp_tags, ff_codec_bmp_tags, ff_codec_wav_tags, 0
};

--> error C2099: Initializer is not a constant

Maybe this isn't fixable though? Not sure

[mstorsjo]

This is not a converter issue but an issue with the code tree itself. Also, --enable-shared builds with libav do work just fine, see e.g. http://fate.libav.org/i686-msvc-10-dll-wine/20130212192512.

[rdp]

I had thought that the purpose of av_export was to allow constants to be shared cross dll's with msvc builds, e.g. this line

libavcodec/mjpeg.h
141:extern av_export const uint8_t avpriv_mjpeg_bits_dc_luminance[];

(which seems to work line).

What's the difference here, anybody know, between that and this line?

libavformat/riff.h
54:extern av_export const AVCodecTag ff_codec_bmp_tags[];

which seems to fail? (I put the av_export in there thinking it would fix msvc builds...)

update: I guess ff_codec_bmp_tags is used differently than "most other shared constants" so will need special treatment... (hence it causing error C2099: Initializer is not a constant but others don't)

(@malbe
Could you try removing the av_export from riff.h and see if that fixes it? I think it won't be enough but worth testing...)

Thanks for your help to this confused developer.
-roger-

[mbechard]

Yes when I removed av_export it works, and the .dlls still export the functions correctly so I guess that's done redundantly elsewhere via another mechanism. I just wanted to report it incase it was unexpected behavior.

[Nevcairiel]

av_export is not needed when exporting a symbol, but actually when importing it. Its a bit misleading that way.

[rdp]

Makes me wonder if av_export is needed at all these days...maybe the use of .v files makes them it needed these days?

[rbultje]

I indeed don't think you need av_export ATM.

[Nevcairiel]

You do need it when importing data from shared libraries in msvc, which is
why it was introduced.

[rbultje]

We enforce that as a linker option instead, I believe?

[rdp]

ok thanks for your help here, git master should compile now, thanks!