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使用Android studio在Ubuntu中编译某个安卓项目时，发现当NDK版本为16时会出现以下错误：

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':libuvccamera:ndkClean'.
> Process 'command '/home/luohanjie/Android/Sdk/ndk/android-ndk-r16b/ndk-build'' finished with non-zero exit value 2

而NDK版本改为20或者21时，则没有问题。

而由于所使用的部分库是使用NDK16版本进行编译的，所以需要对库使用NDK21进行重新编译，但是编译时发生以下问题：

CMakeFiles/allencv.dir/detect/HRB.cpp.o:(.data.rel.ro+0x90): undefined reference to `cv::Feature2D::detect(cv::_InputArray const&, std::__ndk1::vector<cv::KeyPoint, std::__ndk1::allocator<cv::KeyPoint> >&, cv::_InputArray const&)'
CMakeFiles/allencv.dir/detect/HRB.cpp.o:(.data.rel.ro+0x98): undefined reference to `cv::Feature2D::detect(cv::_InputArray const&, std::__ndk1::vector<std::__ndk1::vector<cv::KeyPoint, std::__ndk1::allocator<cv::KeyPoint> >, std::__ndk1::allocator<std::__ndk1::vector<cv::KeyPoint, std::__ndk1::allocator<cv::KeyPoint> > > >&, cv::_InputArray const&)'
CMakeFiles/allencv.dir/detect/HRB.cpp.o:(.data.rel.ro+0xa0): undefined reference to `cv::Feature2D::compute(cv::_InputArray const&, std::__ndk1::vector<cv::KeyPoint, std::__ndk1::allocator<cv::KeyPoint> >&, cv::_OutputArray const&)'
...

最终发现原因是NDK与OpenCV Android发生冲突[1]。新版本的NDK改用libc++作为默认的STL，而OpenCV Android 3.4版本使用的是gnustl。可以升级到OpenCV 4.0版本来兼容新版本的NDK，或者可以使用libc++重新编译OpenCV:

cd $OPENCV_SRC
mkdir build
cd build
export ANDROID_NDK=/home/luohanjie/Android/Sdk/ndk/android-ndk-r21
export ANDROID_SDK_ROOT=/home/luohanjie/Android/Sdk
cmake -DCMAKE_TOOLCHAIN_FILE=/home/luohanjie/Android/Sdk/ndk/android-ndk-r21/build/cmake/android.toolchain.cmake -DANDROID_ABI="arm64-v8a" -DANDROID_STL=c++_static -DCMAKE_BUILD_TYPE=Release -DANDROID_NATIVE_API_LEVEL=android-27 -DANDROID_PLATFORM=27 -DBUILD_TESTS=OFF -DBUILD_PERF_TESTS=OFF -DBUILD_ANDROID_EXAMPLES=OFF -DBUILD_opencv_java=ON -DBUILD_FAT_JAVA_LIB=ON -DBUILD_ANDROID_PROJECTS=ON -DJAVA_AWT_INCLUDE_PATH=/usr/lib/jvm/java-1.8.0-openjdk-amd64/include -DJAVA_AWT_LIBRARY=/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/jawt.h -DJAVA_INCLUDE_PATH=/usr/lib/jvm/java-1.8.0-openjdk-amd64/include -DJAVA_INCLUDE_PATH2=/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/linux -DJAVA_JVM_LIBRARY=/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/jni.h -DANT_EXECUTABLE=/usr/bin/ant -DOPENCV_EXTRA_MODULES_PATH=/home/luohanjie/Documents/software/opencv-3.4.2/opencv_contrib/modules ..
-- General configuration for OpenCV 3.4.2 =====================================
--   Version control:               unknown
-- 
--   Platform:
--     Timestamp:                   2020-06-18T02:57:12Z
--     Host:                        Linux 4.15.0-99-generic x86_64
--     Target:                      Android 1 aarch64
--     CMake:                       3.12.3
--     CMake generator:             Unix Makefiles
--     CMake build tool:            /usr/bin/make
--     Configuration:               Release
-- 
--   CPU/HW features:
--     Baseline:                    NEON FP16
--       required:                  NEON
--       disabled:                  VFPV3
-- 
--   C/C++:
--     Built as dynamic libs?:      NO
--     C++11:                       YES
--     C++ Compiler:                /home/luohanjie/Android/Sdk/ndk/android-ndk-r21/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++  (ver 9.0)
--     C++ flags (Release):         -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security     -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments    -fvisibility=hidden -fvisibility-inlines-hidden -O2 -DNDEBUG   -DNDEBUG
--     C++ flags (Debug):           -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security     -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments    -fvisibility=hidden -fvisibility-inlines-hidden -O0 -fno-limit-debug-info   -DDEBUG -D_DEBUG
--     C Compiler:                  /home/luohanjie/Android/Sdk/ndk/android-ndk-r21/toolchains/llvm/prebuilt/linux-x86_64/bin/clang
--     C flags (Release):           -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security    -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments    -fvisibility=hidden -fvisibility-inlines-hidden -O2 -DNDEBUG   -DNDEBUG
--     C flags (Debug):             -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security    -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments    -fvisibility=hidden -fvisibility-inlines-hidden -O0 -fno-limit-debug-info   -DDEBUG -D_DEBUG
--     Linker flags (Release):      -Wl,--exclude-libs,libgcc_real.a -Wl,--exclude-libs,libatomic.a -static-libstdc++ -Wl,--build-id -Wl,--fatal-warnings -Wl,--no-undefined -Qunused-arguments    
--     Linker flags (Debug):        -Wl,--exclude-libs,libgcc_real.a -Wl,--exclude-libs,libatomic.a -static-libstdc++ -Wl,--build-id -Wl,--fatal-warnings -Wl,--no-undefined -Qunused-arguments    
--     ccache:                      YES
--     Precompiled headers:         NO
--     Extra dependencies:          /home/luohanjie/Android/Sdk/ndk/android-ndk-r21/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/libz.a dl m log
--     3rdparty dependencies:       libcpufeatures libprotobuf libjpeg-turbo libwebp libpng libtiff libjasper IlmImf tegra_hal
-- 
--   OpenCV modules:
--     To be built:                 calib3d core dnn features2d flann highgui imgcodecs imgproc java java_bindings_generator ml objdetect photo python_bindings_generator shape stitching superres video videoio videostab
--     Disabled:                    js world
--     Disabled by dependency:      -
--     Unavailable:                 cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev python2 python3 ts viz
--     Applications:                -
--     Documentation:               NO
--     Non-free algorithms:         NO
-- 
--   Android NDK:                   /home/luohanjie/Android/Sdk/ndk/android-ndk-r21 (ver 21.0.6113669)
--     Android ABI:                 arm64-v8a
--     NDK toolchain:               aarch64-linux-android-clang
--     STL type:                    c++_static
--     Native API level:            27
--   Android SDK:                   /home/luohanjie/Android/Sdk (tools: 24.4.1 build tools: 30.0.0)
--     android tool:                /home/luohanjie/Android/Sdk/tools/android
--     SDK target:                  android-27
--     Projects build scripts:      Ant/Eclipse compatible
-- 
--   GUI: 
-- 
--   Media I/O: 
--     ZLib:                        /home/luohanjie/Android/Sdk/ndk/android-ndk-r21/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/libz.a (ver 1.2.7)
--     JPEG:                        build-libjpeg-turbo (ver 1.5.3-62)
--     WEBP:                        build (ver encoder: 0x020e)
--     PNG:                         build (ver 1.6.34)
--     TIFF:                        build (ver 42 - 4.0.9)
--     JPEG 2000:                   build (ver 1.900.1)
--     OpenEXR:                     build (ver 1.7.1)
--     HDR:                         YES
--     SUNRASTER:                   YES
--     PXM:                         YES
-- 
--   Video I/O:
-- 
--   Parallel framework:            pthreads
-- 
--   Trace:                         YES (built-in)
-- 
--   Other third-party libraries:
--     Custom HAL:                  YES (carotene (ver 0.0.1))
--     Protobuf:                    build (3.5.1)
-- 
--   Python (for build):            /usr/bin/python2.7
-- 
--   Java:                          export all functions
--     ant:                         /usr/bin/ant (ver 1.9.6)
--     Java wrappers:               YES
--     Java tests:                  NO
-- 
--   Install to:                    /home/luohanjie/Documents/software/opencv-3.4.2/build/install
-- -----------------------------------------------------------------
-- 
-- Configuring done
-- Generating done
-- Build files have been written to: /home/luohanjie/Documents/software/opencv-3.4.2/build
make -j4
make install

  1. https://stackoverflow.com/questions/50677231/linking-errors-on-android-with-opencv-3-4-0-and-ndk ↩