I get the following error:
symbol already defined in object
The given symbol, displayed in its decorated form, was multiply defined.
when I include this file more than once: http://www.kuenzle-family.ch/philippe/gl/init_ext.h
in any program…
I can still compile with the linker option /FORCE: MULTIPLE but I really need to find out why it does that…
You should be including that file in precisely, and only, 1 .cpp file. Any more, and you will get linker errors like this.
And you (may) need a corresponding file with the various symbols defined as externs.
But this is basic compiler operation/c/c++ and isn’t really relevant here as it has nothing to do with opengl, advanced or otherwise. I would suggest you do some reading on the extern keyword (plus variable declaration etc) for c++ and post compiler/linker questions on a c++ forum.