VS2019:fatal error C1083 Cannot open header file: 'opencv.hpp' - c++

Question

It is all fine when I was writing the code, that is, when I included the header file "opencv2/opencv.hpp",and VS2019 can indeed "see" it,in other words, I can use the class that is in the opencv.hpp, but only when I complied the project,c1083 occurred
before i added the function DrawLine(),i compiled for times,with no err.and then i added the function DrawLine(..),error occurred
this is the total source code
a.ha.cpp
//a.h
#include<opencv2\opencv.hpp>
using namespace cv;
class Canvas{
Mat mat_canvas;
void Init(){
mat_canvas.create(1024,1024,CV_32FC3);
}
void DrawLine(float ax,float ay,float bx,float by);
}
//a.cpp
#include"a.h"
void Canvas::DrawLine(float ax,float ay,float bx,float by){
cv::line(this->mat_canvas,Point2f(ax,ax),Point2f(bx,by),Scalar(1,1,1));
}
error msg was:
fatal error C1083 Cannot open header file: 'opencv.hpp': no such file or dir
i know i can create a new solution and move my old solution to it,but it takes time,and i can't actually know whether this issue will happen again in my new solution
Any answer will be helpful

Answer 1

Actually there are most of the time possibility of missing "Additional include directory path" or wrongly setup.
Where to find in Visual Studio:
To set this compiler option in the Visual Studio development environment
Open the project's Property Pages dialog box. For details, see Set
C++ compiler and build properties in Visual Studio.
Select the Configuration Properties > C/C++ > General property page.
Modify the Additional Include Directories property.
Visual Studio 2019 C++ Project configuration
Example project setup is described in below link:
Example setup