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std::size_t(3) C++ Standard Libary std::size_t(3) 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 <cuchar> (since C++17) 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). The bit width of std::size_t is not less than 16. (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 seg- mented 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. The integer literal suffix for std::size_t is uz (or UZ). (since C++23) Example // Run this code #include <cstddef> #include <iostream> #include <array> int main() { std::array<std::size_t, 10> a; // Example with C++23 size_t literal for (auto i = 0uz; i != a.size(); ++i) std::cout << (a[i] = i) << ' '; std::cout << '\n'; // Example of decrementing loop for (std::size_t i = a.size(); i--;) std::cout << a[i] << ' '; // Note the naive decrementing loop: // for (std::size_t i = a.size() - 1; i >= 0; --i) ... // is an infinite loop, because unsigned numbers are always non- negative } Output: 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1 0 References * C++20 standard (ISO/IEC 14882:2020): * 6.8.3 Compound types [basic.compound] (p: 75-76) * 7.6.2.5 Sizeof [expr.sizeof] (p: 129-130) * 7.6.2.6 Alignof [expr.alignof] (p: 130) * 17.2.4 Sizes, alignments, and offsets [sup- port.types.layout] (p: 507-508) * C++17 standard (ISO/IEC 14882:2017): * 6.9.2 Compound types [basic.compound] (p: 81-82) * 8.3.3 Sizeof [expr.sizeof] (p: 121-122) * 8.3.6 Alignof [expr.alignof] (p: 129) * 21.2.4 Sizes, alignments, and offsets [sup- port.types.layout] (p: 479) * C++14 standard (ISO/IEC 14882:2014): * 3.9.2 Compound types [basic.compound] (p: 73-74) * 5.3.3 Sizeof [expr.sizeof] (p: 109-110) * 5.3.6 Alignof [expr.alignof] (p: 116) * 18.2 Types [support.types] (p: 443-444) * C++11 standard (ISO/IEC 14882:2011): * 5.3.3 Sizeof [expr.sizeof] (p: 111) * 5.3.6 Alignof [expr.alignof] (p: 116) * 18.2 Types [support.types] (p: 454-455) * C++03 standard (ISO/IEC 14882:2003): * 5.3.3 Sizeof [expr.sizeof] (p: 79) * C++98 standard (ISO/IEC 14882:1998): * 5.3.3 Sizeof [expr.sizeof] (p: 77) Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior CWG 1122 C++98 the definition of size_t was in the it is imple- mentation-defined C standard (<stddef.h>) See also ptrdiff_t signed integer type returned when subtracting two pointers (typedef) byte offset from the beginning of a standard-layout type to offsetof specified member (function macro) binary, integer literals (since C++14) decimal, octal, or hexadecimal num- bers of integer type http://cppreference.com 2022.07.31 std::size_t(3)
NAME | Synopsis | Notes | Example | Output: | References | See also
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