std::ranges::cbegin

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

(since C++20)

Returns an iterator to the first element of the const-qualified argument.

(until C++23)

Returns a constant iterator to the first element of the argument.

(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::cbegin is expression-equivalent to ranges::begin (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::cbegin is expression-equivalent to:

• std::const_iterator <decltype(U)>(U) for some expression U equivalent to ranges::begin (possibly-const-range (t).

In all other cases, a call to ranges::cbegin is ill-formed, which can result in substitution failure when the call appears in the immediate context of a template instantiation.

(since C++23)

• 1 Customization point objects
• 2 Notes
• 3 Example
• 4 See also

ranges::begin (std::as_const (e)).

(until C++23)

• ranges::begin (e) if T models constant_range.
• Otherwise, ranges::begin (std::as_const (e)) if const T models constant_range.
• Otherwise, std::basic_const_iterator (ranges::begin (e)).

(since C++23)

#include <cassert>
#include <ranges>
#include <vector>
 
int main()
{
 std::vector v{3, 1, 4};
 auto vi = std::ranges::cbegin(v);
 assert (3 == *vi);
 ++vi; // OK, constant-iterator object is mutable
 assert (1 == *vi);
 // *vi = 13; // Error: constant-iterator points to an immutable element
 
 int a[]{3, 1, 4};
 auto ai = std::ranges::cbegin(a); // cbegin works with C-arrays as well
 assert (3 == *ai and *(ai + 1) == 1);
 // *ai = 13; // Error: read-only variable is not assignable
}

returns an iterator to the beginning of a range
(customization point object)[edit]

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