Ubuntu20.04安装OpenCV3.20报错及解决

1. /usr/include/c++/9/cstdlib:75:15: fatal error: stdlib.h: 没有那个文件或目录 解决：cmake时加上参数-D ENABLE_PRECOMPILED_HEADERS=OFF

2. error: 'CODEC_FLAG_GLOBAL_HEADER' was not declared in this scope 解决：opencv/opencv-3.2.0/modules/videoio/src/cap_ffmpeg_impl.hpp 里最顶端添加了3

   #define AV_CODEC_FLAG_GLOBAL_HEADER (1 << 22)
   #define CODEC_FLAG_GLOBAL_HEADER AV_CODEC_FLAG_GLOBAL_HEADER
   #define AVFMT_RAWPICTURE 0x0020`

3. make[2]: *** [modules/python3/CMakeFiles/opencv_python3.dir/build.make:56: modules/python3/CMakeFiles/opencv_python3.dir/__/src2/cv2.cpp.o] Error 1make[1]: *** [CMakeFiles/Makefile2:21149: modules/python3/CMakeFiles/opencv_python3.dir/all] Error 2
   解决：找cv2.cpp,将

   char* str = PyString_AsString(obj);

   改为

   char* str = (char *)PyString_AsString(obj);