Building with libc++ on OSX

[sarith]

Hey there,

I've been having a great time working with this excellent library. I'm currently trying to incorporate it into a C++ project I need to build with libc++. Can someone point me in the right direction for compiling the libessentia binary against libc++ (and not libstdc++)?

I've compiled/installed all the dependencies for Essentia via Homebrew as instructed in the documentation. Would I need to recompile the dependencies with clang++/libc++ as well?

Sorry for what might be a basic question - this is my first time getting this involved with the compile/link process.

Thanks so much,
S

[wackou]

Well, this is trickier than it seems...

Normally, you should just uncomment those lines: https://github.com/MTG/essentia/blob/master/wscript#L65

However, if you do that, then this file doesn't compile anymore: https://github.com/MTG/essentia/blob/master/src/base/roguevector.h

And the problem lies in the fact that the RogueVector class relies on an implementation detail of the C++ library which uses protected inheritance in libstdc++, so we can override its behavior, but uses private inheritance in libc++... There is actually no clean way to do this with libc++, so we're stuck with libstdc++ at the moment (which is not very nice when developing with clang/libc++, I agree...).

The correct and clean solution would be to replace all uses of std::vector in Essentia using a new essentia::Vector class that would also give us the behavior of the RogueVector class (ie: can "borrow" memory from another vector, required for the streaming mode). That is however quite some bit of work...

[sarith]

I completely understand. I wish I had the necessary skills to contribute a solution to this issue.

In the meantime, I suppose one workable solution for my prototype would be to compile my extractor as a command line utility, execute the utility from my "host" application, write the algorithm results to a file, and then read/parse the file contents to my host libc++ application.

If anyone else has any ideas, input would be greatly appreciated.

[wackou]

Compiling the extractor as a command-line utility seems the best choice:

• a crash in Essentia doesn't crash your host app
• it is very easily parallelizable if you want to run an extractor on lots of files; you can also have a task queue distribute jobs depending on the number of cores available to optimize CPU usage (very adapted to running lots of tasks on a cluster)
• you get the build system for the extractor nearly "for free", just add yours in the src/examples and edit the https://github.com/MTG/essentia/blob/master/src/examples/wscript file to add it.

[loretoparisi]

I just came across the same issue when trying to build Essentia on mobile iOS.
I ported FFTW to iOS/armv7 using this script that works (quite) good:

http://stackoverflow.com/questions/3588904/how-to-link-third-party-libraries-like-fftw3-and-sndfile-to-an-iphone-project-in

Then I put everything in XCode5 and build.

Now the error is exactly the problem depicted here:

Without having the libc++ flags active I have:

/Users/loreto/Projects/iOS/AUDIO/EssentiaTouch/EssentiaTouch/Classes/essentia/roguevector.h:127:40: No member named '_M_impl' in 'essentia::RogueVector'

My question here is

Is possibile to use instead Apple "veclib.h" from Accelerate.Framework here ?

I mean

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk/System/Library/Frameworks/Accelerate.framework/Frameworks/vecLib.framework/Headers/vecLib.h

[wackou]

the problem here is that the RogueVector class relies on an implementation detail of the std::vector class from the gnu libstdc++ that gcc links to. Clang however links against libc++ which has a different implementation and doesn't allow the RogueVector to be implemented on top of it, because all its member variables are private (they are protected in libstdc++).

If you could compile using libstdc++ instead of libc++ that should make it work.

Otherwise, the better (but more time consuming) solution would be to implement a custom vector class that would allow the RogueVector to be implemented, and change all the buffers in the streaming mode to use that vector class (instead of std::vector currently)

[loretoparisi]

I agree that the best solution would it be to implement the custom vector class. So far I'm compiling against libstdc++ and it works fine on LLVM5.0 / armv7.

That was operating in standard mode, due to too much native IO limitation with the streaming mode on armv7 devices.

Hope to see a RogueVector specific implementation and a huge refactoring then!

[wackou]

The latest version of master now builds against libc++ instead of libstdc++ on mac os. It's a big fat hack but it works, so that's what it is :-) The correct fix is still to move most of Essentia to a specific essentia::Vector (and essentia::Matrix to replace tnt::Array2D), but that will be for a later version. In the meantime, it should now compile everywhere using the native compiler and C++ standard lib (should also work on iphone, although I haven't tested it)