如何将Opus链接到您的Visual Studio项目？

Question

I wanted to play around with opus some so i downloaded opus 1.1 however it seems like i cant really link it to my visual studio 2010 express project. I tried adding the opus1.1/include path to properties/vc++Directoris/include Directories, but the linker still complains about some of the functions

error LNK2019: unresolved external symbol _opus_decoder_create referenced in function ...
error LNK2019: unresolved external symbol _opus_decoder_destroy referenced in function...
error LNK2019: unresolved external symbol _opus_encoder_destroy referenced in function...
error LNK2019: unresolved external symbol _opus_encoder_ctl referenced in function...
error LNK2019: unresolved external symbol _opus_encode referenced in function...
error LNK2019: unresolved external symbol _opus_decode referenced in function...

Any help would be appriciated!

Answer 1

opus1.1 / win32中有一个.sln文件，可在Visual Studio 2010中打开该文件并进行编译以进行调试和发布，然后创建.lib文件。

Answer 2

C++ libraries usually consist of header files (for the compiler) and library files (for the linker). You only provided header files but no library files, so the linker complains. The include path is only for header files and has nothing to do with the linker [*].

The library you downloaded probably contains some *.lib file. That's the file needed by the linker. In Visual Studio, specify the directory of the file at "VC++ Directories > Library Directories" (preferably in the so-called "Property Manager" window), and in your project settings, specify the *.lib file at "Linker > Input > Additional Dependencies".

Now here's the difficulty: you must make sure that your project is compiled with the same runtime-library setting the *.lib file was built with. For example, if the *.lib file was built with /MD, then you must do the same. If the *.lib file is not provided in the (for you) correct way, then you will eventually want to build the library yourself.

[*] Actually, in MSVC, you can have auto-linking via header files, a technique used by some Boost libraries, but let's ignore this for now.

Answer 3

The reason is that the "Windows" distribution of opusfile is compiled with mingw64, and generates .a link libraries, as well as traditional .dll files. Thus, there is no straightforward way to link opusfile with Visual Studio.

This means that, as supplied, you can only use mingw64 to link against the "Windows" distribution, which, if you ask me, is not doing most Windows-based developers any favors.

"./configure && make" is how you built UNIX-style software, and requires a large set of text processing support tools (automake, autoconf, a Bourne-like shell, etc) as well as, usually, GCC, rather than the platform-native compiler on Windows.

The right answer is to generate .lib files, either by porting all the code in the distribution to Visual Studio on your own (lots of work) or by generating link libraries from the DLLs: http://support.microsoft.com/kb/131313/en-us

Note that, in general, this doesn't work -- it only works if the library API is C-based (not C++ based) and if there are no mis-matched allocations (where you do alloc, and library does free, or vice versa) and if the compiler that generated the .dll files is ABI compatible with Visual Studio.

You can also generate the linkable libs by generating a "stub" library with empty implementations, and use the .lib from that, or you can use dynamic loading using LoadLibrary() and GetProcAddress().

So, yeah, the libopusfile developers weren't being particularly helpful to the vast majority of Windows-based developers when building the "windows" version of the library.

Btw: I had problems with this very unhelpful SDK myself, and I solved them, and re-packaged the solution for Visual Studio. This includes additional header files that were necessary but not included, as well as generating a .lib linkable library from the functions found using dumpbin. Note that this has not been extensively tested, but I have a working opus file playback tool based on this:

http://www.enchantedage.com/opusfile-0.6-for-visual-studio

This includes the headers and .lib file needed for Visual Studio.