安装好后opencv后执行下面这条语句的时候出错：
pkg-config --cflags opencv
Package opencv was not found in the pkg-config search path.
Perhaps you should add the directory containing `opencv.pc'
to the PKG_CONFIG_PATH environment variable
No package 'opencv' found
经过网上详细查询资料后，是缺失了opencv.pc这个配置信息文件，故解决方法就是添加这个文件然后将其导入到环境变量中，具体操作如下：
首先创建opencv.pc文件，这里要注意它的路径信息：
cd /usr/local/lib sudo mkdir pkgconfig cd pkgconfig sudo touch opencv.pc
然后在opencv.pc中添加以下信息，注意这些信息需要与自己安装opencv时的库路径对应：
prefix=/usr/local
exec_prefix=${prefix}
includedir=${prefix}/include
libdir=${exec_prefix}/lib
Name: opencv
Description: The opencv library
Version:4.0.1
Cflags: -I${includedir}/opencv4
Libs: -L${libdir} -lopencv_shape -lopencv_stitching -lopencv_objdetect -lopencv_superres -lopencv_videostab -lopencv_calib3d -lopencv_features2d -lopencv_highgui -lopencv_videoio -lopencv_imgcodecs -lopencv_video -lopencv_photo -lopencv_ml -lopencv_imgproc -lopencv_flann -lopencv_core
保存退出，然后将文件导入到环境变量：
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
至此就配置好opencv.pc啦～
再执行 pkg-config --cflags --libs opencv时输出结果如下：
-I/usr/local/include/opencv4 -L/usr/local/lib \
-lopencv_stitching -lopencv_objdetect \
-lopencv_calib3d \
-lopencv_features2d -lopencv_highgui -lopencv_videoio \
-lopencv_imgcodecs -lopencv_video -lopencv_photo -lopencv_ml \
-lopencv_imgproc -lopencv_flann -lopencv_core