Question

I do know that ~0 will evaluate the maximum word sized bit 1s (and thus takes caring of portability), but I am still not getting why ((1 << N) – 1) is discouraged?

Please share if you used the second form and got into any trouble.

Answer 1

Look at these lines:

1. printf("%X", ~(~0 << 31) );
2. printf("%X", (1 << 31) - 1 );

Line 1 compiles and behaves like expected.

Line 2 gives the warning integer overflow in expression.

This is because 1 << 31 is treated by default as a signed int, so 1 << 31 = -2147483648, which is the smallest possible integer.

As a result, resting 1 causes an overflow.