MinGW C++ compiler cant find OpenCV in the system path - c++

Question

So I'm getting an error stating "fatal error: opencv2\core\mat.hpp: No such file or directory" when trying to compile a small c++ file from .cpp with MinGW. It happens in one form or another in Sublime Text 3, Atom, and on the command line with "gcc myfile.cpp". I should note that I'm on Windows 10. Here's the code:
#include <iostream>
#include <opencv2\core\mat.hpp>
#include <opencv2\core.hpp>
#include <opencv2\highgui.hpp>
#include <opencv2\core\types.hpp>
#include <opencv2\imgproc.hpp>
int main()
{
std::cout << "Hello World!\n";
cv::Mat img = cv::imread("despair.jpg");
cv::cvtColor(img, img, cv::COLOR_RGBA2GRAY, 1);
cv::imshow("1", img);
cv::waitKey(0);
cv::Mat mask = cv::Mat(img.rows, img.cols, CV_8UC1, cv::Scalar(255));
cv::Rect_ <char> roi = cv::Rect_ <cv::Point>(cv::Point(0, 0), cv::Point(10, 10));
cv::rectangle(mask, roi, cv::Scalar(0), -1);
cv::Scalar colors = cv::mean(img, mask);
}
Things I've done and tried:
Adding C:\OpenCV\opencv\build\include\ to the system path.
Adding the bin and lib folders in x64/vc15 folder to the system path.
Messing and experimenting with the system path in general to try to find anything that might work. (I've tried so many combinations at this point I've forgotten most of them)
Adding everything to my user specific path.
Changing the include directory in the .cpp file to be the absolute path to each file I need to include (This works for the exact files I need, but then fails when those files try to include other files they need, like when Mat.hpp tries to include Matx.hpp)
Reinstalling MinGW64.
Installing MinGW to different folders and updating the system path to reflect the new location.
Changing which text editor I'm using
Compiling from the command line outside of a text editor
Things in my system path right now:
C:\OpenCV\opencv\build\x64\vc15\lib
C:\OpenCV\opencv\build\x64\vc15\bin
C:\OpenCV\opencv\build\include\
C:\MinGW\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin
I took this code out of a larger project to test what was going on with it and at this point I'm at my wits end trying to figure out what's wrong. Please send help.

Answer 1

Add -I option with path to opencv includes and -L with path to opencv libraries, like this:
gcc -IC:\OpenCV\opencv\build\include -LC:\OpenCV\opencv\build\x64\vc15\lib test_opencv.cpp