Question: I have downloaded qt-5.0.0 for windows. 

<http://releases.qt-project.org/qt5/5.0.1/qt-windows-opensource-5.0.1-msvc2010_32-x86-offline.exe>

I have added INCLUDEPATH += C:\opencv\build\include in the .pro file.

Opencv 2.4.3 is already installed.

When I include header file in qtcreator :

```
#include <opencv2/opencv.hpp> 

```

There is compilation error : can not find opencv2/opencv.hpp

Any ideas ??

Answer: 
I found the solution. In Qt Creator, goto Projects on the left pane ( ctrl+5), then Build Environment -> Use System Environment, click on Details. Edit LIB variable. Add here.
The correct header files are:

```
<opencv2/core/core.hpp>
<opencv2/imgproc/imgproc.hpp>
<opencv2/highgui/highgui.hpp>

```

… and so on. The include of "opencv.h" is deprecated!
It also does not work anymore for QtCreator auto-completion.

The solution is to update your sources to use the correct header files.