在linux下编译android下的opencv，使用cmake的方法

cmake -DCMAKE_BUILD_WITH_INSTALL_RPATH=ON           -DCMAKE_TOOLCHAIN_FILE="/home/ahfu/opencv-3.4.6/platforms/android/android.toolchain.cmake"           -DANDROID_NDK="/home/ahfu/android-ndk-r14b"           -DANDROID_NATIVE_API_LEVEL=24           -DANDROID_ABI="armeabi-v7a"           -DANDROID_CPP_FEATURES="rtti exceptions"           -DANDROID_ARM_NEON=TRUE           -DANDROID_STL=gnustl_static           -DCMAKE_BUILD_TYPE=Release           -DOPENCV_EXTRA_MODULES_PATH="/home/ahfu/opencv_contrib-3.4.6/modules"            -DCMAKE_INSTALL_PREFIX="/home/ahfu/opencv_3.4.6_install/"           -D BUILD_opencv_java=OFF           -D BUILD_ANDROID_PROJECTS=OFF           -D BUILD_ANDROID_EXAMPLES=OFF           -D BUILD_DOCS=OFF           -D BUILD_PERF_TESTS=OFF           -D BUILD_TESTS=OFF           
          -D BUILD_FAT_JAVA_LIB=OFF       
-D  BUILD_opencv_apps    =ON -D  BUILD_opencv_aruco    =ON -D  BUILD_opencv_bgsegm   =ON -D  BUILD_opencv_bioinspired  =ON -D  BUILD_opencv_calib3d   =OFF -D  BUILD_opencv_ccalib   =ON -D  BUILD_opencv_core    =ON -D  BUILD_opencv_datasets   =ON -D  BUILD_opencv_dnn    =ON -D  BUILD_opencv_dnn_objdetect  =ON -D  BUILD_opencv_dpm    =ON -D  BUILD_opencv_face    =ON -D  BUILD_opencv_features2d  =OFF -D  BUILD_opencv_flann    =ON -D  BUILD_opencv_fuzzy    =ON -D  BUILD_opencv_hfs    =ON -D  BUILD_opencv_highgui   =OFF -D  BUILD_opencv_img_hash   =ON -D  BUILD_opencv_imgcodecs   =ON -D  BUILD_opencv_imgproc   =ON -D  BUILD_opencv_java_bindings_gen =OFF -D  BUILD_opencv_js    =OFF -D  BUILD_opencv_line_descriptor =ON -D  BUILD_opencv_ml    =ON -D  BUILD_opencv_objdetect   =ON -D  BUILD_opencv_optflow   =ON -D  BUILD_opencv_phase_unwrapping =ON -D  BUILD_opencv_photo    =ON -D  BUILD_opencv_plot    =ON -D  BUILD_opencv_reg  =ON -D  BUILD_opencv_rgbd    =ON -D  BUILD_opencv_saliency   =ON -D  BUILD_opencv_shape    =ON -D  BUILD_opencv_stereo   =ON -D  BUILD_opencv_stitching  =ON -D  BUILD_opencv_structured_light =ON -D  BUILD_opencv_superres   =ON -D  BUILD_opencv_surface_matching =ON -D  BUILD_opencv_text    =ON -D  BUILD_opencv_tracking   =ON -D  BUILD_opencv_video   =ON -D  BUILD_opencv_videoio   =ON -D  BUILD_opencv_videostab  =ON -D  BUILD_opencv_world   =ON -D  BUILD_opencv_xfeatures2d  =OFF -D  BUILD_opencv_ximgproc   =ON -D  BUILD_opencv_xobjdetect  =ON -D  BUILD_opencv_xphoto =ON -D  WITH_ARITH_DEC    =ON -D  WITH_ARITH_ENC    =ON -D  WITH_CAROTENE     =ON -D  WITH_CLP      =ON -D  WITH_CPUFEATURES    =ON -D  WITH_CUDA      =OFF -D  WITH_FFMPEG     =ON -D  WITH_GDCM      =ON -D  WITH_GSTREAMER_0_10   =ON -D  WITH_HALIDE     =ON -D  WITH_IMGCODEC_HDR    =ON -D  WITH_IMGCODEC_PXM    =ON -D  WITH_IMGCODEC_SUNRASTER  =ON -D  WITH_INF_ENGINE  =ON -D  WITH_ITT     =ON -D  WITH_JASPER    =ON -D  WITH_JPEG     =ON -D  WITH_OPENCL    =OFF -D  WITH_OPENCL_SVM   =OFF -D  WITH_OPENEXR    =ON -D  WITH_OPENMP    =ON -D  WITH_OPENVX    =ON -D  WITH_PNG     =ON -D  WITH_PROTOBUF    =ON -D  WITH_PTHREADS_PF   =ON -D  WITH_QUIRC     =ON -D  WITH_TBB     =ON -D  WITH_TIFF     =ON -D  WITH_WEBP  =ON           ../

//jpg2bmp.cpp
#include <stdio.h>
#include <inttypes.h>
#include <opencv2/opencv.hpp>
#include <opencv2/core.hpp>

#ifndef P
#define P(format,...) do   {     printf("%s %s %d " format "n",__FILE__,__FUNCTION__,__LINE__,##__VA_ARGS__);     fflush(stdout);   }   while (0);
#endif

int main(int argc,char* argv[]){
    if (argc<3){
        printf("usage:%s <from> <to>n",argv[0]);
        return 0;
    }
    cv::Mat image = cv::imread(argv[1],cv::IMREAD_UNCHANGED);
    if (image.empty()){
        P("load pic %s fail",argv[1]);
        return -1;
    }
    cv::Mat bmp;
    cv::cvtColor(image,bmp,cv::COLOR_BGR2GRAY);   
    cv::imwrite(argv[2],bmp);
    P("ok");
    return 1;
}

/*
ndk-build NDK_LOG=1 V=1 NDK_DEBUG=1 NDK_PROJECT_PATH=$(pwd) NDK_APPLICATION_MK=./Application.mk APP_BUILD_SCRIPT=./Android.mk
*/

APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions -std=c++11 -fPIC
#注意：-fPIC一定要加，否则可执行程序在android上执行出现以下错误：
#     Android 5.0 and later only support position-independent executables (-fPIE).

APP_PLATFORM := android-24
# 注意：APP_PLATFORM一定要等于或者高于opencv编译时候的版本
#      否则链接的时候出现大量类似错误  undefined reference to ‘rand‘
APP_ABI := armeabi-v7a

include $(CLEAR_VARS)

LOCAL_PATH := ./


LOCAL_C_INCLUDES:=/home/ahfu/opencv_3.4.6_install/sdk/native/jni/include

LOCAL_ARM_NEON := true      
LOCAL_CFLAGS:=-g -pie -fPIC -DANDROID_ARM_NEON=TRUE -DANDROID_TOOLCHAIN=clang
LOCAL_LDLIBS +=    -L"/home/ahfu/opencv_3.4.6_install/sdk/native/staticlibs/armeabi-v7a" -lopencv_core -lopencv_imgcodecs -lopencv_imgproc -lm -lz -landroid -llog   -L"/home/ahfu/opencv_3.4.6_install/sdk/native/3rdparty/libs/armeabi-v7a" -ltegra_hal -lcpufeatures -llibpng -llibjpeg-turbo -llibtiff -llibjasper -llibwebp -lIlmImf   -lopencv_core -lopencv_imgcodecs -lopencv_imgproc -ltegra_hal   -L"/home/ahfu/android-ndk-r14b/sources/cxx-stl/gnu-libstdc++/4.9/libs/armeabi-v7a/"   -lgnustl_static -ldl
#注意：链接阶段出现了大量stl链接时候的错误
#     不明原因，但是我强制指定了STL的链接目录，问题解决
#     链接目录：android-ndk-r14b/sources/cxx-stl/gnu-libstdc++/4.9/libs/armeabi-v7a/
#     链接库  -lgnustl_static

LOCAL_MODULE := jpg2bmp

LOCAL_SRC_FILES := jpg2bmp.cpp


LOCAL_LDLIBS +=  -lm -llog
include $(BUILD_EXECUTABLE)