How do I know which version of OpenGL I am using?

Question

I started writing programs, in C (for now) using GLFW and OpenGL. The question I have is that, how do I know which version of OpenGL my program will use? My laptop says that my video card has OpenGL 3.3. Typing "glxinfo | grep -i opengl" returns:

OpenGL vendor string: NVIDIA Corporation OpenGL renderer string: GeForce 9600M GT/PCI/SSE2 OpenGL version string: 3.3.0 NVIDIA 285.05.09 OpenGL shading language version string: 3.30 NVIDIA via Cg compiler OpenGL extensions: 

So is OpenGL 3.3 automatically being used ?

Answer 1

Just call glGetString(GL_VERSION) (once the context is initialized, of course) and put out the result (which is actually the same that glxinfo does, I suppose):

printf("%s\n", glGetString(GL_VERSION)); 

Your program should automatically use the highest possible version your hardware and driver support, which in your case seems to be 3.3. But for creating a core-profile context for OpenGL 3+ (one where deprecated functionality has been completely removed) you have to take special measures. But since version 2.7 GLFW has means for doing this, using the glfwOpenWindowHint function. But if you don't want to explicitly disallow deprecated functionality, you can just use the context given to you by the default context creation functions of GLFW, which will as said support the highest possible version for your hardware and drivers.

But also keep in mind that for using OpenGL functionality higher than version 1.1 you need to retrieve the corresponding function pointers or use a library that handles this for you, like GLEW.