cmake if test for GCC

Question

What is the correct way to test if the compiler is GCC under Cmake?

I've seen both if(CMAKE_COMPILER_IS_GNUCC) and if(CMAKE_COMPILER_IS_GNUXX) but neither of those are defined when I run cmake. Just to be clear, I'm 100% sure I'm using GCC.

I just want to add compiler flags specific to GCC. Previously I just used an else clause after a check fro windows, but I want to be more generic now.

Answer 1

I think I found the problem. Those properties aren't defined until after the project statement. Switching the ordering around and it appears to work.