std::size_t (3) - Linux Man Pages
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
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.
// Run this code
offsetof (function macro)