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ndk-build编译失败¶

问题一¶

/home/zj/Android/Sdk/ndk-bundle/build/ndk-build
Android NDK: android-8 is unsupported. Using minimum supported version android-16.    
Android NDK: WARNING: APP_PLATFORM android-16 is higher than android:minSdkVersion 1 in /home/zj/Documents/PICC/android/numberocr/src/main/AndroidManifest.xml. NDK binaries will *not* be compatible with devices older than android-16. See https://android.googlesource.com/platform/ndk/+/master/docs/user/common_problems.md for more information.    
Android NDK: ERROR:/home/zj/Documents/PICC/android/numberocr/src/main/jni/Android.mk:opencv_contrib: LOCAL_SRC_FILES points to a missing file    
Android NDK: Check that /home/zj/Android/OpenCV-android-sdk/sdk/native/jni/../libs/arm64-v8a/libopencv_contrib.a exists  or that its path is correct   
/home/zj/Android/Sdk/ndk-bundle/build/core/prebuilt-library.mk:45: *** Android NDK: Aborting    .  Stop.

查找arm64-v8a/libopencv_contrib.a是否存在，设置Application.mk编译平台为

APP_ABI := armeabi-v7a

问题二¶

/home/zj/Android/Sdk/ndk-bundle/build/ndk-build
Android NDK: android-8 is unsupported. Using minimum supported version android-16.    
Android NDK: WARNING: APP_PLATFORM android-16 is higher than android:minSdkVersion 1 in /home/zj/Documents/PICC/android/numberocr/src/main/AndroidManifest.xml. NDK binaries will *not* be compatible with devices older than android-16. See https://android.googlesource.com/platform/ndk/+/master/docs/user/common_problems.md for more information.    
Android NDK: WARNING:/home/zj/Documents/PICC/android/numberocr/src/main/jni/Android.mk:IDNumberOCR: non-system libraries in linker flags: -latomic    
Android NDK:     This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES    
Android NDK:     or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the    
Android NDK:     current module    
/home/zj/Documents/PICC/android/numberocr/src/main/obj/local/armeabi-v7a/objs/IDNumberOCR/main.o.d:1: *** target pattern contains no `%'.  Stop.

参考：android ndk-build 时出现target pattern contain no % 的解决方法

删除obj文件夹（这个文件夹伴随着libs一起生成）里的.o文件，重新ndk-build即可

问题三¶

7:14: fatal error: 'array' file not found

参考：解决ndk-build : fatal error: 'iostream' file not found

新建Application.mk，添加

APP_STL := c++_static

问题三¶

/home/zj/Documents/PICC/android/faceocr/src/main/jni/main.cpp:11:8: error: expected unqualified-id
extern "C" {
    ^
1 error generated.
make: *** [/home/zj/Documents/PICC/android/faceocr/src/main/obj/local/arm64-v8a/objs/FaceOCR/main.o] Error 1

参考:expected unqualified-id before ....的问题

在其他头文件的类定义中需要再默认添加分号

问题四¶

undefined reference to `cv::CascadeClassifier::detectMultiScale

参考:OpenCV - undefined reference to 'cv::CascadeClassifier::detectMultiScale() after NDK update

设置Application.mk中的C++标准库

APP_STL := gnustl_static

最新的NDK不再支持gnustl,所以下载之前版本的NDK进行编译

# 最新
Latest Stable Version (r19b)
# 之前版本
Android NDK, Revision 16b (December 2017)