OpenCV hello world not compiling like it should

Question

I am setting up a new machine with OpenCV 2.3.1. The machine is a Windows 7 box, and I followed the installation instructions given by the OpenCV website (used CMake with MinGW to build).

Here is my code:

#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
int main() {
    char var;
    cv::Mat img;
    img = cv::imread("C:/test/img.jpg");
    cv::namedWindow("Image");
    cv::imshow("Image", img);
    std::cin >> var;
    return 1;
}

Here is my make command:

g++ -o main main.cpp -lopencv_core -lopencv_imgproc -lopencv_calib3d -lopencv_video -lopencv_features2d -lopencv_ml -lopencv_highgui -lopencv_objdetect -lopencv_contrib -lopencv_legacy

Here is my path:

C:\OpenCV-2.3.1\install\bin;C:\OpenCV-2.3.1\install\include;C:\QtSDK\QtCreator\bin;C:\Program Files (x86)\MiKTeX 2.9\miktex\bin;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\CMake 2.8\bin;C:\QtSDK\mingw\bin;

Here is my error:

main.cpp:2:33: error: opencv2/core/core.hpp: No such file or directory
main.cpp:3:39: error: opencv2/highgui/highgui.hpp: No such file or directory
main.cpp: In function 'int main()':
main.cpp:8: error: 'cv' has not been declared
main.cpp:8: error: expected ';' before 'img'
main.cpp:9: error: 'img' was not declared in this scope
main.cpp:9: error: 'cv' has not been declared
main.cpp:10: error: 'cv' has not been declared
main.cpp:11: error: 'cv' has not been declared

This is not making sense. Why won't this compile? Why can't it find opencv2/core/core.hpp?

Solution

g++ doesn't consider %PATH% ($PATH on Unix) when looking for include files.

Add the following to the compilation command: -IC:\OpenCV-2.3.1\install\include:

g++ -IC:\OpenCV-2.3.1\install\include -o main main.cpp -lopencv_core ...