std::size_t (3) Linux Manual Page

std::size_t – std::size_t

Synopsis

Defined in header <cstddef>

Defined in header <cstdio>

Defined in header <cstdlib>

Defined in header <cstring>

Defined in header <ctime>

Defined in header <cwchar>

typedef /*implementation-defined*/ size_t;

std::size_t is the unsigned integer type of the result of the sizeof operator
as well as the sizeof… operator and the alignof operator
(since C++11).

Notes

std::size_t can store the maximum size of a theoretically possible object of any type (including array).
A type whose size cannot be represented by std::size_t is ill-formed
(since C++14) On many platforms (an exception is systems with segmented addressing) std::size_t can safely store the value of any non-member pointer, in which case it is synonymous with std::uintptr_t.
std::size_t is commonly used for array indexing and loop counting. Programs that use other types, such as unsigned int, for array indexing may fail on, e.g. 64-bit systems when the index exceeds UINT_MAX or if it relies on 32-bit modular arithmetic.
When indexing C++ containers, such as std::string, std::vector, etc, the appropriate type is the member typedef size_type provided by such containers. It is usually defined as a synonym for std::size_t.

Example

// Run this code

#include <cstddef>

#include <iostream>

#include <array>
int main()

{
    std::array<std::size_t, 10> a;
    for (std::size_t i = 0; i != a.size(); ++i)
        a[i] = i;
    for (std::size_t i = a.size() - 1; i < a.size(); --i)
        std::cout << a[i] << " ";
}

Output:

  9 8 7 6 5 4 3 2 1 0

See also

          signed integer type returned when subtracting two pointers
ptrdiff_t (typedef)
          byte offset from the beginning of a standard-layout type to specified member
offsetof (function macro)