Include path confusion in Qt with Eclipse

Hi there,

I'm running Eclipse integrated with Qt. Have a simple project and now I want to test introducing a 3rd party header-only "library".

So, I right-click on the project entry in the Project Explorer, choose Properties... In the dialog, I click "Add External Include Path..." and type in the directory containing the header files.

Then I go to a .cpp file within the project and #include the file. It fails to build saying that the header file cannot be found!!!!!

So I remove the external include path and edit the .pro file and use INCLUDEPATH += path/to/headers. That works.

I'm struggling to understand how there's 2 ways to do the same thing and only 1 of them works. Hopefully someone can explain why it "works" like this?

Thanks,

PUK