std::ranges::crbegin

(since C++20)
(customization point object)

(since C++20)

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)).

(until C++23)

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.

(since C++23)

#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})>>
 );
}

returns a reverse iterator to a range
(customization point object)[edit]

returns a reverse iterator to the beginning of a container or array
(function template) [edit]