C++ SDL What does the | do?

Question

screen = SDL_SetVideoMode(1000,1000,32, SDL_HWSURFACE | SDL_FULLSCREEN);

What does the | do in SDL_HWSURFACE | SDL_FULLSCREEN

Answer 1

The | operator means bitwise or. That means each bit in the result is set if the corresponding bit in the left hand or the right hand value is set. So 1 | 2 = 3, because 1 in binary is 01 and 2 in binary is 10. So the result in binary is 11 which is 3 in decimal.

In your example this is used to pass a lot of different on/off options to a function. Each of the constants has exactly one bit set. The function then looks at the value you pass and using the bitwise and operator & to check which ones you specified.