std::ranges::crbegin
<ranges>
<iterator>
inline constexpr /* unspecified */ crbegin = /* unspecified */;
(customization point object)
requires /* see below */
Returns an iterator to the first element of the const-qualified argument that is treated as a reversed sequence.
(until C++23)Returns a constant iterator to the first element of the argument that is treated as a reversed sequence.
(since C++23)Let CT
be
- const std::remove_reference_t <T>& if the argument is an lvalue (i.e.
T
is an lvalue reference type), - const T otherwise.
A call to ranges::crbegin
is expression-equivalent to ranges::rbegin (static_cast<CT&&>(t)).
If the argument is an lvalue or ranges::enable_borrowed_range <std::remove_cv_t <T>> is true, then a call to ranges::crbegin
is expression-equivalent to:
- std::const_iterator <decltype(U)>(U) for some expression U equivalent to ranges::rbegin (
possibly-const-range
(t)).
In all other cases, a call to ranges::crbegin
is ill-formed, which can result in substitution failure when the call appears in the immediate context of a template instantiation.
The return type models std::input_or_output_iterator and constant-iterator
(since C++23) in all cases.
Customization point objects
The name ranges::crbegin
denotes a customization point object, which is a const function object of a literal semiregular
class type. See CustomizationPointObject for details.
[edit] Example
#include <cassert> #include <iterator> #include <span> #include <vector> int main() { std::vector <int> v{3, 1, 4}; auto vi = std::ranges::crbegin(v); assert (*vi == 4); ++vi; // OK, iterator object is mutable assert (*vi == 1); // *vi = 13; // Error: underlying element is read-only int a[]{-5, 10, 15}; auto ai = std::ranges::crbegin(a); assert (*ai == 15); // auto x_x = std::ranges::crbegin(std::vector<int>{6, 6, 6}); // ill-formed: the argument is an rvalue (see Notes ↑) auto si = std::ranges::crbegin(std::span {a}); // OK assert (*si == 15); static_assert ( std::ranges::enable_borrowed_range <std::remove_cv_t <decltype(std::span {a})>> ); }
[edit] See also
(function template) [edit]