I'm am planning to use CoreGraphics for its low-level functionality, so I wrote up a small snippet that I expected to work: #include <CoreGraphics/CoreGraphics.h> int main() { double rot = CGDisplayRotation(0); printf("Rotation %f\n", rot); return 0; } Unfortunately, it seems that the call CGDisplayRotation blocks. When I tried writing a similar snippet in XCode though, it works just fine but I will not be able to use XCode for unrelated reasons. Am I compiling incorrectly? Could this be a permission issue? I compiled with clang -Wall -framework CoreGraphics core.c -o core.o