std::size_t

From Cppreference

std::size_t is the unsigned integer type of the result of the sizeof operator.

[edit] Notes

size_t can store the maximum size of a theoretically possible object of any type (including array), which means, on most platforms, that a variable of std::size_t type 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.

[edit] Example

#include <cstddef>
int main()
{
    const std::size_t N = 100;
    int* a = new int[N];
    for(std::size_t n = 0; n<N; ++n)
        a[n] = n;
    delete[] a;
}

[edit] See also