std::ranges::cbegin

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)

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)

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

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)
`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)

Example

#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
}

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

std::ranges::cbegin

Customization point objects

Notes

Example

See also