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std::ranges:: cbegin

From cppreference.net
C++
Ranges library
Range adaptors
Defined in header <ranges>
Defined in header <iterator>
inline namespace /* unspecified */ {

inline constexpr /* unspecified */ cbegin = /* unspecified */ ;

}
(since C++20)
(customization point object)
Call signature
template < class T >

requires /* see below */

constexpr /* see below */ auto cbegin ( T && t ) ;
(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)

range-begin-end.svg

Let CT be

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:

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)

The return type models std::input_or_output_iterator and constant-iterator (since C++23) in all cases.

Contents

Customization point objects

The name ranges::cbegin denotes a customization point object , which is a const function object of a literal semiregular class type. See CustomizationPointObject for details.

Notes

For an lvalue range e of type T , ranges :: cbegin ( e ) is equivalent to

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

(until C++23)
(since C++23)

Example

Run this code 
#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
}

See also

(C++20)
returns an iterator to the beginning of a range
(customization point object)
(C++11) (C++14)
returns an iterator to the beginning of a container or array
(function template)