Linking FFTW into an Android NDK application

Question

I am currently writing a genre classification application as my final year project in Computer Engineering. I initially wrote the feature extraction code (implementing FFTW) in C and now I need to implement it on Android via the NDK.

This is my first NDK project so I'm still getting the hang of things but I have compiled the FFTW3 library for Android according to this guide. I didn't do the very last step because I didn't think it was right for what I need.

My question is how do I, after the compile step, use the library in the main NDK application that calls on it? Do I everything normally in Application.mk just with LOCAL_STATIC_LIBRARIES set to the libfftw3.a that I just compiled? And then I don't need to have any -lfftw3 linker flags like I normally would right?

Answer 1

You can use prebuit FFTW library (no matter how did you build it).

Or you can build FFTW in Android.mk makefile with the whole project.

Android.mk content will be:

# Prebuilt FFTW library
include $(CLEAR_VARS)
LOCAL_MODULE := fftw
include $(PREBUILT_STATIC_LIBRARY)

# or

# Build FFTW library
include $(CLEAR_VARS)
LOCAL_MODULE := fftw
# TODO put your static libs build flags
include path_to_fftw_sources/$(LOCAL_MODULE).mk
include $(BUILD_STATIC_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE := YourProject
# TODO put your shared lib build flags
include path_to_your_project/$(LOCAL_MODULE).mk
LOCAL_STATIC_LIBRARIES += fftw
include $(BUILD_SHARED_LIBRARY)

I have written path_to_fftw_sources/$(LOCAL_MODULE).mk for building fftw static library and path_to_your_project/$(LOCAL_MODULE).mk for building your shared library. It is often better to put LOCAL_SRC_FILES and LOCAL_C_INCLUDES to the separate .mk file.

You can read more about Android.mk file in docs/ANDROID-MK.html document in your NDK distribution.