Bit mask in C

Question

What is the best way to construct a bit mask in C with m set bits preceded by k unset bits, and followed by n unset bits:

00..0 11..1 00..0   k     m     n 

For example, k=1, m=4, n=3 would result in the bit mask:

01111000 

Answer 1

~(~0 << m) << n

Answer 2

So, you are asking for m set bits prefixed by k reset bits and followed by n reset bits? We can ignore k since it will largely be constrained by the choice of integer type.

mask = ((1 << m) - 1) << n;