std::ranges::cbegin

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata reserve_hint (C++26)   empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    common_range	sized_range viewable_range    view	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	approximately_sized_range (C++26) constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while common_viewviews::common views::counted to_input_viewviews::to_input (C++26)(C++26)	ref_view drop_viewviews::drop drop_while_viewviews::drop_while lazy_split_viewviews::lazy_split split_viewviews::split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   concat_viewviews::concat (C++26)(C++26) cache_latest_viewviews::cache_latest (C++26)(C++26)	owning_view reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

Defined in header <ranges>
Defined in header <iterator>
inlinenamespace/* unspecified */{     inlineconstexpr/* 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 conststd::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 literalsemiregular 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

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 mutableassert(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 wellassert(3==*ai and *(ai +1)==1);// *ai = 13; // Error: read-only variable is not assignable}

See also

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)