add 'extern "C"' to headers

[spraff]

Your policy at the moment is to require applications to add 'extern "C"' to their C++ source files: ​http://trac.ffmpeg.org/wiki/Including%20FFmpeg%20headers%20in%20a%20C%2B%2B%20application

This is silly and annoying.

It is the header file's job to present its interface consistently to applications. decklink_enc.h does this, the other headers should too.

[Clément Bœsch]

We have about 85 C public headers currently. Am I correct to assume that you are asking us to add a C++ boilerplate cruft for every one of them?

Note that in addition to clutter the public header read by our downstreams, it will suggest that FFmpeg headers are C++ compatible, which is NOT the case because it uses C99 specific features in various places, which are not supported by the C++ language.

[Carl Eugen Hoyos]

The headers are C headers and I believe this documented. If you want to use the library with another compiler language, it is your responsibility to ensure the necessary steps are taken.

[jwakely]

Could this wontfix decision be revisited? Would you accept a patch to add the necessary boilerplater?

The current situation causes every C++ project that uses ffmpeg headers to deal with it, which then causes other problems downstream. The documented way to include ffmpeg headers from C++ sources violates the C++ standard. The standard says you can't include any standard header (such as <math.h>) inside an extern "C" declaration.

Which C99 features are used which would cause a problem? Apparently it doesn't cause a problem, because many C++ projects such as Qt do include the headers. But they have to violate the C++ standard to do so, and the fall out from that can be harder for those projects to work around (it requires changes in the C++ standard library implementation to accommodate your policy).

[Cigaes]

Carl Eugen Hoyos's answer is still valid. Adding this in our headers would imply we *support* it, which we do not.

[jwakely]

Why couldn't you just continue to document that C++ is not officially supported, but still accept a patch so that it mostly Just Works, even though not supported?

The reality is that people are already using your headers in C++ code, but they're forced to do so badly and in violation of the standard.

[jwakely]

The current policy seems to be hostile to a large number of users.