Opencv4.1链接so错误（android sdk) error: undefined reference to 'cv::error(int, std::string const...

如果遇到链接错误，一般是lib的路径不对，但是显然这次不是，错误如下：

native/jni/include\opencv2/core/mat.inl.hpp:548: error: undefined reference to 'cv::error(int, std::string const&, char const*, char const*, int)'native/jni/include\opencv2/core/mat.inl.hpp:561: error: undefined reference to 'cv::error(int, std::string const&, char const*, char const*, int)'xxx_std.h:355: error: undefined reference to 'cv::putText(cv::_InputOutputArray const&, std::string const&, cv::Point_, int, double, cv::Scalar_, int, int, bool)'

显然是链上了，但是找不到特定函数的实现，比如error() ,imread(),imwrite()等等

幸而stackover上opencv4.0.1已经有过这个问题了，见链接

根本原因是NDK从r16开始就切换到了llvm的libC++，所以opencv4从libstdC++切换到了libc++。

导致链接错误的根本原因是设置了-DANDRID_STL=gnustl_shared，因为opencv利用的libc++编的，而非gnustl

所以build.gradle设置成-DANDROID_STL=c++_shared即可，参照：

 externalNativeBuild {            cmake {               //sample cpp flag parameters                cppFlags "-std=c++14 -Ofast -Rpass-analysis=loop-vectorize -fsave-optimization-record -fdiagnostics-show-hotness"           //sample abi filter parameters                abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'    //set -DANDROID_STL to c++_shared                arguments "-DANDROID_STL=c++_shared"             }        }

done!

如果有需求从opencv4降到opencv3，很多废弃的宏定义可能也够喝一壶，添加一个头文件：

/* * OpenCV 4.0.1 backward compatibility header. * */#ifndef ANDROID_DOXCAPTUREUI_OPENCV4_COMPAT_H#define ANDROID_DOXCAPTUREUI_OPENCV4_COMPAT_H#include #include #if CV_MAJOR_VERSION > 3// namespace cv;//{#ifndef CV_TERMCRIT_ITER#define CV_TERMCRIT_ITER cv::TermCriteria::MAX_ITER#endif#ifndef CV_BGR2GRAY#define CV_BGR2GRAY cv::COLOR_BGR2GRAY#endif#ifndef CV_BGR2RGB#define CV_BGR2RGB cv::COLOR_BGR2RGB#endif#ifndef CV_RGB2GRAY#define CV_RGB2GRAY cv::COLOR_RGB2GRAY#endif#ifndef CV_BGRA2GRAY#define CV_BGRA2GRAY cv::COLOR_BGRA2GRAY#endif#ifndef CV_GRAY2RGBA#define CV_GRAY2RGBA cv::COLOR_GRAY2RGBA#endif#ifndef CV_GRAY2RGB#define CV_GRAY2RGB cv::COLOR_GRAY2RGB#endif#ifndef CV_GRAY2BGRA#define CV_GRAY2BGRA cv::COLOR_GRAY2BGRA#endif#ifndef CV_GRAY2BGR565#define CV_GRAY2BGR565 cv::COLOR_GRAY2BGR565#endif#ifndef CV_RGBA2BGR565#define CV_RGBA2BGR565 cv::COLOR_RGBA2BGR565#endif#ifndef CV_RGBA2RGB#define CV_RGBA2RGB cv::COLOR_RGBA2RGB#endif#ifndef CV_RGB2RGBA#define CV_RGB2RGBA cv::COLOR_RGB2RGBA#endif#ifndef CV_RGB2BGR565#define CV_RGB2BGR565 cv::COLOR_RGB2BGR565#endif#ifndef CV_RGBA2BGR#define CV_RGBA2BGR cv::COLOR_RGBA2BGR#endif#ifndef CV_RGBA2GRAY#define CV_RGBA2GRAY cv::COLOR_RGBA2GRAY#endif#ifndef CV_ADAPTIVE_THRESH_GAUSSIAN_C#define CV_ADAPTIVE_THRESH_GAUSSIAN_C cv::ADAPTIVE_THRESH_GAUSSIAN_C#endif#ifndef CV_THRESH_BINARY#define CV_THRESH_BINARY cv::THRESH_BINARY#endif#ifndef CV_BGR2HSV#define CV_BGR2HSV cv::COLOR_BGR2HSV#endif#ifndef CV_BGR2Lab#define CV_BGR2Lab cv::COLOR_BGR2Lab#endif#ifndef CV_RGB2HSV#define CV_RGB2HSV cv::COLOR_RGB2HSV#endif#ifndef CV_HSV2RGB#define CV_HSV2RGB cv::COLOR_HSV2RGB#endif#ifndef CV_THRESH_OTSU#define CV_THRESH_OTSU cv::THRESH_OTSU#endif#ifndef CV_THRESH_BINARY#define CV_THRESH_BINARY THRESH_BINARY#endif#ifndef CV_MOP_CLOSE#define CV_MOP_CLOSE cv::MORPH_CLOSE#endif#ifndef CV_RETR_CCOMP#define CV_RETR_CCOMP cv::RETR_CCOMP#endif#ifndef CV_RETR_LIST#define CV_RETR_LIST cv::RETR_LIST#endif#ifndef CV_RETR_TREE#define CV_RETR_TREE cv::RETR_TREE#endif#ifndef CV_RETR_FLOODFILL#define CV_RETR_FLOODFILL cv::RETR_FLOODFILL#endif#ifndef CV_RETR_EXTERNAL#define CV_RETR_EXTERNAL cv::RETR_EXTERNAL#endif#ifndef CV_CHAIN_APPROX_SIMPLE#define CV_CHAIN_APPROX_SIMPLE cv::CHAIN_APPROX_SIMPLE#endif#ifndef CV_CHAIN_APPROX_TC89_KCOS#define CV_CHAIN_APPROX_TC89_KCOS cv::CHAIN_APPROX_TC89_KCOS#endif#ifndef CV_FILLED#define CV_FILLED cv::FILLED#endif#ifndef CV_REDUCE_SUM#define CV_REDUCE_SUM cv::REDUCE_SUM#endif#ifndef CV_StsBadArg#define CV_StsBadArg cv::Error::StsBadArg#endif//}#ifndef cvFastArctan#define cvFastArctan( Y, X )  ( std::atan2( (Y), (X) ) )#endif#endif //endif CV_MAJOR_VERSION#endif //ANDROID_DOXCAPTUREUI_OPENCV4_COMPAT_H

参考： stackover

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