In the long run when you start to need extensions, might find benefit using the cross-platform extension helper library called glew. I find it much easier than having to use GetProcAddress queries for every extension imaginable.
Basically all you have to do is add two lines of code
#include <GL/glew.h>
... after your window is created then
glewInit();
... now extensions available for you to use!
A foll0w up – GLEW allows you to simplify and ignore the details as posted at Beyond Windows ogl 1.1. It is worthwhile to read this just to see why helper libraries like GLEW are so valuable.