cv编译报错：error: xxx was not declared in this scope； did you mean xxx?

报错：

这种一般都是由于opencv3升级到opencv4之后，名词不统一导致的。

比如下面这些报错：

error: ‘cvCreateMat’ was not declared in this scope; did you mean ‘cvCreateSparseMat’?
error: ‘cvMulTransposed’ was not declared in this scope
error: ‘CV_SVD_MODIFY_A’ was not declared in this scope; did you mean ‘CV_HAL_SVD_MODIFY_A’
error: ‘CV_SVD_U_T’ was not declared in this scope
error: ‘cvSVD’ was not declared in this scope
error: ‘cvReleaseMat’ was not declared in this scope
error: ‘CV_SVD’ was not declared in this scope; did you mean ‘CV_AVX’?
error: ‘cvInvert’ was not declared in this scope; did you mean ‘cvInvSqrt’?
error: ‘cvCreateMat’ was not declared in this scope; did you mean ‘cvCreateSparseMat’?
error: ‘cvMulTransposed’ was not declared in this scope
error: ‘CV_SVD_MODIFY_A’ was not declared in this scope; did you mean ‘CV_HAL_SVD_MODIFY_A’?
error: ‘CV_SVD_MODIFY_A’ was not declared in this scope; did you mean ‘CV_HAL_SVD_MODIFY_A’?

解决方法：

一、添加头文件

#include 

还有一些是要加这个

#include 

不知道加哪一个就都加上

二、按照提示修改

比如上面报错的图，里面有绿色的字，把红色改成绿色即可，有些没法改，就加头文件试试。