Question

I have an enum declaration using bit flags and I cant exactly figure out on how to use this.

enum 
{
  kWhite   = 0,
  kBlue    = 1 << 0,
  kRed     = 1 << 1,
  kYellow  = 1 << 2,
  kBrown   = 1 << 3,
};
typedef char ColorType;

I suppose to store multiple colors in one colorType I should OR the bits together?

ColorType pinkColor = kWhite | kRed;

But suppose I would want to check if pinkColor contains kRed, how would I do this?

Anyone care to give me an example using the provided ColorType example ?

Answer 1

Yes, use bitwise OR (|) to set multiple flags:

ColorType pinkColor = kWhite | kRed;

Then use bitwise AND (&) to test if a flag is set:

if ( pinkColor & kRed )
{
   // do something
}

The result of & has any bit set only if the same bit is set in both operands. Since the only bit in kRed is bit 1, the result will be 0 if the other operand doesn’t have this bit set too.

If you need to get whether a particular flag is set as a BOOL rather than just testing it in an if condition immediately, compare the result of the bitwise AND to the tested bit:

BOOL hasRed = ((pinkColor & kRed) == kRed);