std::size_t

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

#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] << " ";
}

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See also