std::size_t (3) - Linux Manuals

std::size_t: std::size_t

NAME

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