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std::ranges::cbegin(3) C++ Standard Libary std::ranges::cbegin(3) NAME std::ranges::cbegin - std::ranges::cbegin Synopsis Defined in header <ranges> inline namespace /*unspecified*/ { inline constexpr /*unspecified*/ cbegin = (since C++20) /*unspecified*/; (customiza- tion point object) } Call signature template< class T > requires /* see below */ (since C++20) constexpr std::input_or_output_iterator auto cbegin( T&& t ); Returns an iterator to the first element of the const-qualified ar- gument. range-begin-end.svg Let CT be 1. const std::remove_reference_t<T>& if the argument is a lvalue (i.e. T is an lvalue reference type), 2. const T otherwise, a call to ranges::cbegin is expression-equivalent to ranges::begin(static_cast<CT&&>(t)). The return type models std::input_or_output_iterator in both cases. Expression-equivalent Expression e is expression-equivalent to expression f, if * e and f have the same effects, and * either both are constant subexpressions or else neither is a constant subexpression, and * either both are potentially-throwing or else neither is poten- tially-throwing (i.e. noexcept(e) == noexcept(f)). Customization point objects The name ranges::cbegin denotes a customization point object, which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __cbegin_fn. All instances of __cbegin_fn are equal. The effects of invoking dif- ferent instances of type __cbegin_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, ranges::cbegin can be copied freely and its copies can be used in- terchangeably. Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to ranges::cbegin above, __cbegin_fn models * std::invocable<__cbegin_fn, Args...>, * std::invocable<const __cbegin_fn, Args...>, * std::invocable<__cbegin_fn&, Args...>, and * std::invocable<const __cbegin_fn&, Args...>. Otherwise, no function call operator of __cbegin_fn participates in overload resolution. Example // Run this code #include <iostream> #include <ranges> #include <vector> int main() { std::vector<int> v = { 3, 1, 4 }; auto vi = std::ranges::cbegin(v); std::cout << *vi << '\n'; // *vi = 42; // Error: read-only variable is not assignable int a[] = { -5, 10, 15 }; auto ai = std::ranges::cbegin(a); std::cout << *ai << '\n'; // *ai = 42; // Error: read-only variable is not assignable } Output: 3 -5 See also ranges::begin returns an iterator to the beginning of a range (C++20) (customization point object) begin cbegin returns an iterator to the beginning of a container or array (C++11) (function template) (C++14) http://cppreference.com 2022.07.31 std::ranges::cbegin(3)
NAME | Synopsis | Example | Output: | See also
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