Arsthbt

I've seen both (size_t)-1 and ~0 used to represent large numbers, or numbers with all their bits flipped.

Is there any difference between the two? If so, what is it?

I found this question: What is the difference between -1 and ~0, however it did not answer my question because I'm dealing with unsigned integers (such as size_t), as opposed to signed integers (such as int).

What's the difference between (size_t)-1 and ~0?

Type and value differ.

(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.

~0 is often -1 and has the type of int.

Assigning both of those to a size_t will result in SIZE_MAX.

size_t a = (size_t)-1; 
size_t b = ~0;

In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.

(size_t)-1 is of type size_t. It typically has a value of 2³²-1 or 2⁶⁴-1 (4294967295 or 18446744073709551615).

~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).

Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.

If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.

Note that the previous answers assume a 2s complement machine (very likely to be the case these days, but not guaranteed).

If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1s complement machine then -1 would have all bits but the LSB set.

In all of these cases (including the common 2s complement machine) ~0 has all bits set.