bitwise check if flag present

Question

Is there a method typically used to check if a flag is present in an int/other data type? I figured out something like this:

if ((host&flagtocheckfor)==flagtocheckfor) 

Which works fine- however it's such a common method of setting flags is this the way flags are usually checked? Or is there a more concise method?

Answer 1

That's pretty well exactly the way bit flags are checked in most languages that support them.

For example:

#define BIT_7 0x80 #define BITS_0_AND_1 0x03  if ((flag & BIT_7) == BIT_7) ... if ((flag & BITS_0_AND_1) == BITS_0_AND_1) ... 

While you can check something like the first with:

if ((flag & BIT_7) != 0) ... 

that won't actually work for the second since it will return true if either of the bits are set, not both.

For completeness, C allows you to set the bit masks with:

flag = flag | BIT_7;   // or you can also use 'flag |= BIT_7' 

You can clear them with:

flag = flag & (~BIT_7); 

And toggle them with:

flag = flag ^ BIT_7;