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posted Dec 1, 2014, 2:44 AM by Javad Taghia


Defined in header <cstddef>
Defined in header <cstdio>
Defined in header <cstring>
Defined in header <ctime>
Defined in header <cstdlib>
(since C++11)
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).


std::size_t can store the maximum size of a theoretically possible object of any type (including array). On many platforms (an exception are 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::stringstd::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
#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;

See also

signed integer type returned when subtracting two pointers 
byte offset from the beginning of a standard-layout type to specified member 
(function macro)
C documentation for size_t