函数传参cv::Mat, const cv::Mat, const cv::Mat& or cv::Mat& 的区别

引用自:

https://stackoverflow.com/questions/23468537/differences-of-using-const-cvmat-cvmat-cvmat-or-const-cvmat/23486280

1. cv::Mat Input: pass a copy of Input's header. Its header will not be changed outside of this function, but can be changed within the function. For example:

   void sillyFunc(cv::Mat Input, cv::Mat& Output){
       Input = cv::Mat::ones(4, 4, CV_32F); // OK, but only changed within the function
       //...
   }

2. const cv::Mat Input: pass a copy of Input's header. Its header will not be changed outside of or within the function. For example:

   void sillyFunc(const cv::Mat Input, cv::Mat& Output){
       Input = cv::Mat::ones(4, 4, CV_32F); // Error, even when changing within the function
       //...
   }

3. const cv::Mat& Input: pass a reference of Input's header. Guarantees that Input's header will not be changed outside of or within the function. For example:

   void sillyFunc(const cv::Mat& Input, cv::Mat& Output){
       Input = cv::Mat::ones(4, 4, CV_32F); // Error when trying to change the header
       ...
   }

4. cv::Mat& Input: pass a reference of Input's header. Changes to Input's header happen outside of and within the function. For example:

   void sillyFunc(cv::Mat& Input, cv::Mat& Output){
       Input = cv::Mat::ones(4, 4, CV_32F); // totally OK and does change
       ...
   }