C++ flags and the bitwise OR operator

The result of the bitwise OR is a single value. Other than what the actual result is, it's no different from

SDL_INIT(SDL_INIT_VIDEO + SDL_INIT_JOYSTICK)

Addition adds two values and returns the result, which is passed to the function. Bitwise OR also takes two operands and returns the result.

so lets say

 SDL_INIT_VIDEO 

is equal to 1 and

 SDL_INIT_JOYSTICK 

is equal to 4. so that means 1 | 4. so in binary is it going to be

00000001
00000100
-----------
00000101

which means 5.

and how does the function work with that?

Probably something like this:

To expand on that... some common operations using flags.

1) You have to assume that each "flag" is a unique bit pattern, so that no two flags share bits unless they mean the same thing.
2) You can combine any flags with |

flagC = (flagA | flagB)

yields some integer that contains the information of both flags.

3) You can test for a flag with &

(flagC & flagA) => flagA

any non-zero result from the flag test means that the flag was there.

You can combine your flags in a test as well

(flagC & (flagA | flagB) ) => flagA | flagB

4) You can remove a flag with 'not' and 'and'

flagC & ~flagA => flagB

For something like collision, you could do tests like:

if( objectFlags & (ENEMY | ZOMBIE) == (ENEMY | 0) ){// do effect that hurts any enemy that is not a zombie...}if( objectFlags & (ENEMY) ){// do effects that hurt all enemies...}if( objectFlags & (ZOMBIE) ){// do effects that only hurt zombies...}

whre objectFlags is a single number generated from ORing together flags like

ENEMY = 1<<0ZOMBIE = 1<<1PLAYER = 1<<2ENVIRONMENT = 1<<3

note: 1<1<<0 = 0001
1<<1 = 0010
1<<2 = 0100
...etc
the >> operator does the oposite, but has some special considerations on signed numbers.
For unsigned numbers, it yields
0100 >> 2 = 0001