error: undefined reference to `cv::imread(cv::String const&, int)' 解决方法

编译时出现下列错误：

undefined reference to 'cv::imread(cv::String const&, int)'
undefined reference to 'cv::String::deallocate()'
undefined reference to 'cv::imread(cv::String const&, int)'
undefined reference to 'cv::String::deallocate()'
undefined reference to 'cv::String::allocate(unsigned long)'
undefined reference to 'cv::String::allocate(unsigned long)'
undefined reference to 'cv::String::deallocate()'
undefined reference to 'cv::String::deallocate()'

解决方法：在CMakeLists.txt加入安装OpenCV的版本号：
将
find_package( OpenCV REQUIRED )
更改为
find_package( OpenCV 3 REQUIRED ) 。