passing flags to a function

[solemn dirge]

hello, for example in sdl you can pass more then one flag to a function, how do they do that ? a lot of if statements ?

[robust scarab]

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[proud scarab]

in libraries like SDL those flags usually represent one bit each, so they can just be OR'd together

[forest zinc]

well if they are actually flags you bitwise add them togheter

[proud scarab]

function(flag1 | flag2 | flag3);

[solemn dirge]

yes but how they know to use all of them

[primal shore]

oh, that part is an if statement based on some condition you want to check

[solemn dirge]

so just a lot a lot if statements ?

[primal shore]

you bitwise or them together, so it's one if statement per flag.

[solemn dirge]

for example SDL_WINDOW_RESIZABLE | SDL_WINDOW_SHOWN | SDL_WINDOW_BORDERLESS

its different from SDL_WINDOW_BORDERLESS | SDL_WINDOW_SHOWN

[primal shore]

yes, so you make a variable to hold the flags

well in this case

SDL_WINDOW_RESIZABLE is probably more of a you decision as a developer

should the window be resizeable or not?

but for example SDL_WINDOW_BORDERLESS might depend on if the user wants borderless full screen or windowed mode

[solemn dirge]

oh i think i got it for example the bitwise is [01101] and there is option with [01001] it will only activate the second and last flags ?

[primal shore]

I think you are describing a bitwise and?

but I'm not sure why you are asking

[proud scarab]

enum flags : uint32_t {
    a = 1 << 0; // 0x01
    b = 1 << 1; // 0x02
    c = 1 << 2; // 0x04
    d = 1 << 3; // 0x08
    e = 1 << 4; // 0x10
    f = 1 << 5; // 0x20
    g = 1 << 6; // 0x40
    h = 1 << 7; // 0x80
};

uint32_t obj_state{ 0 };
// set the 3rd bit
obj_state |= flags::c;
// unset the 5th bit
obj_state &= ~flags::e;
// check if 1st bit is high
bool state = 0 != (obj_state & flags::a);

// count high bits
int32_t set_bits = 0;
for (uint32_t i = 0; i < sizeof(obj_state) * 8; ++i)
    if (0 != ((obj_state >> i) & 0b1))
        ++set_bits;

you can do a bunch of stuff using bit flags, i think that would be most common examples there