NDK 编译常见问题总结

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1. dlopen failed:"lib_xyz.so"is64-bit instead of 32-bit 这个表示你编译出来的是64bit，但是你应用的地方是32bit，

这时你应该修改一下APP_ABI， from arm64-v8a to armeabi-v7a

#APP_ABI := arm64-v8a
APP_ABI := armeabi-v7a

2.dlsym failed: undefined symbol: sobel_filter

这表示你可能用C++编译器编译的，需要再编译引用的函数名前extern "C" like this

extern "C" int sobel_filter(uchar* pInImg,uchar* pOutImg,int width,int height);

3. 学会使用dlerror打印错误原因， dl 动态库详解http://blog.csdn.net/jernymy/article/details/6903683

4. 学会使用extern “C" http://www.jianshu.com/p/5d2eeeb93590

5. armeabi-v7a（32位ARM设备），arm64-v8a（64位ARM设备）

6. applicate.mk 详解 http://blog.sina.com.cn/s/blog_602f877001014ptu.html

一个简单的opencv 例子使用NDK 编译

Android.mk

LOCAL_PATH:= $(call my-dir)include $(CLEAR_VARS)OPENCV_LIB_TYPE=STATIC#include $(OPENCV_ANDROID_ROOT)/sdk/native/jni/OpenCV.mkinclude C:/workspace/OpenCV-3.0.0-android-sdk-1/OpenCV-android-sdk/sdk/native/jni/OpenCV.mkLOCAL_MODULE    := libplat_recogLOCAL_CFLAGS    := -WerrorLOCAL_SRC_FILES := plat_recog.cpp#LOCAL_LDLIBS    += -llog -landroid -lEGL -lGLESv1_CMLOCAL_LDLIBS    += -llog #build dynamic libraryinclude $(BUILD_SHARED_LIBRARY)

Application.mk

LOCAL_PATH:= $(call my-dir)include $(CLEAR_VARS)OPENCV_LIB_TYPE=STATIC#include $(OPENCV_ANDROID_ROOT)/sdk/native/jni/OpenCV.mkinclude C:/workspace/OpenCV-3.0.0-android-sdk-1/OpenCV-android-sdk/sdk/native/jni/OpenCV.mkLOCAL_MODULE    := libplat_recogLOCAL_CFLAGS    := -WerrorLOCAL_SRC_FILES := plat_recog.cpp#LOCAL_LDLIBS    += -llog -landroid -lEGL -lGLESv1_CMLOCAL_LDLIBS    += -llog #build dynamic libraryinclude $(BUILD_SHARED_LIBRARY)

plat_recog.cpp

#include <opencv2/opencv.hpp>#include <android/log.h>#define  LOG_TAG    "plate_recognition"#define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)using namespace cv;extern "C" int sobel_filter(uchar* pInImg,uchar* pOutImg,int width,int height);int sobel_filter(uchar* pInImg,uchar* pOutImg,int width,int height){  if(pInImg == NULL){    LOGE("input is null!");    return -1;  }  /*  CV_8UC1: single channel  CV_8UC2: two channels  CV_8UC3: three channels  */  Mat srcImg(height,width,CV_8UC1,pInImg);  Mat outImg(height,width,CV_8UC1,pOutImg);  Sobel(srcImg, outImg, outImg.depth(), 1, 0, 3);  imwrite("test.jpg",outImg);  memcpy(pInImg,pOutImg,width*height);  LOGE("sobel filter is done");  return 0;}

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