What is a portable method to find the maximum value of size_t?

Question

I'd like to know the maximum value of size_t on the system my program is running. My first instinct was to use negative 1, like so:

size_t max_size = (size_t)-1;

But I'm guessing there's a better way, or a constant defined somewhere.

Answer 1

A manifest constant (a macro) exists in C99 and it is called SIZE_MAX. There's no such constant in C89/90 though.

However, what you have in your original post is a perfectly portable method of finding the maximum value of size_t. It is guaranteed to work with any unsigned type.

Answer 2

#define MAZ_SZ (~(size_t)0)

or SIZE_MAX

Answer 3

As an alternative to bit-operations suggested in the other answers, you could do this in C++

#include <limits>
size_t maxvalue = std::numeric_limits<size_t>::max()

Answer 4

The size_t max_size = (size_t)-1; solution suggested by the OP is definitely the best so far, but I did figure out another, more convoluted, way to do this. I'm posting it just for academic curiosity.

#include <limits.h>

size_t max_size = ((((size_t)1 << (CHAR_BIT * sizeof(size_t) - 1)) - 1) << 1) + 1;

Answer 5

If you are assuming at least C++11 compiler then SIZE_MAX should be available to you:

http://en.cppreference.com/w/c/types/limits