At one point I was porting between different C stacks. I found they would compile just fine. It was when you looked into the details of the different CRT functions you would have some real fun. For example printf is an evil function of randomness, where the parameters are identical but the way it would decode that input string was highly dependent on when it was written and which stack it was in. Now today you have basically 3 different compilers you have to worry about and they mostly act the same now. It is just as you move between libs that it can sometimes get a bit crazy if they use any sort of if/def to change the way some features work (glaring at you pthreads).