std::begin, std::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)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) output_iterator (C++20) forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (deprecated in C++17)	incrementable_traits (C++20) indirectly_readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)   indirect_unary_predicate (C++20)	indirect_binary_predicate (C++20) indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20) indirectly_copyable_storable (C++20)	indirectly_swappable (C++20) indirectly_comparable (C++20) permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)
Iterator adaptors
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) make_const_iterator (C++23) make_const_sentinel (C++23) back_inserter front_inserter inserter
Stream iterators
istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
Iterator customization points
ranges::iter_move (C++20)
ranges::iter_swap (C++20)
Iterator operations
advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
Range access
begincbegin (C++11)(C++14) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

Defined in header <array>
Defined in header <deque>
Defined in header <forward_list>
Defined in header <iterator>
Defined in header <list>
Defined in header <map>
Defined in header <regex>
Defined in header <set>
Defined in header <span>		(since C++20)
Defined in header <string>
Defined in header <string_view>		(since C++17)
Defined in header <unordered_map>
Defined in header <unordered_set>
Defined in header <vector>
	(1)
template< class C > auto begin( C& c ) -> decltype(c.begin());			(since C++11) (until C++17)
template< class C > constexpr auto begin( C& c ) -> decltype(c.begin());			(since C++17)
		(1)
template< class C > auto begin( const C& c ) -> decltype(c.begin());				(since C++11) (until C++17)
template< class C > constexpr auto begin( const C& c ) -> decltype(c.begin());				(since C++17)
			(2)
template< class T, std::size_t N > T* begin( T (&array)[N] );					(since C++11) (until C++14)
template< class T, std::size_t N > constexpr T* begin( T (&array)[N] ) noexcept;					(since C++14)
template< class C > constexpr auto cbegin( const C& c ) noexcept(/* see below */)     -> decltype(std::begin(c));				(3)	(since C++14)

Returns an iterator to the beginning of the given range.

1) Returns exactly c.begin(), which is typically an iterator to the beginning of the sequence represented by c. If C is a standard Container, this returns C::iterator when c is not const-qualified, and C::const_iterator otherwise.

2) Returns a pointer to the beginning of the array.

3) Returns exactly std::begin(c), with c always treated as const-qualified. If C is a standard Container, this always returns C::const_iterator.

Parameters

c	-	a container or view with a begin member function
array	-	an array of arbitrary type

Return value

An iterator to the beginning of the range.

Exceptions

3)

noexcept specification:  

noexcept(noexcept(std::begin(c)))

Overloads

Custom overloads of begin may be provided for classes and enumerations that do not expose a suitable begin() member function, yet can be iterated. The following overloads are already provided by the standard library:

std::begin(std::initializer_list) (C++11)	overloads std::begin (function template)
std::begin(std::valarray) (C++11)	overloads std::begin (function template)
begin(std::filesystem::directory_iterator)end(std::filesystem::directory_iterator) (C++17)	range-based for loop support (function)
begin(std::filesystem::recursive_directory_iterator)end(std::filesystem::recursive_directory_iterator)	range-based for loop support (function)

Similar to the use of swap (described in Swappable), typical use of the begin function in generic context is an equivalent of using std::begin; begin(arg);, which allows both the ADL-selected overloads for user-defined types and the standard library function templates to appear in the same overload set.

template<typename Container, typename Function>
void for_each(Container&& cont, Function f) {
    using std::begin;
    auto it = begin(cont);
    using std::end;
    auto end_it = end(cont);
    while (it != end_it) {
        f(*it);
        ++it;
    }
}

Overloads of begin found by argument-dependent lookup can be used to customize the behavior of std::ranges::begin, std::ranges::cbegin, and other customization pointer objects depending on std::ranges::begin.

(since C++20)

Notes

(1,3) exactly reflect the behavior of C::begin(). Their effects may be surprising if the member function does not have a reasonable implementation.

std::cbegin is introduced for unification of member and non-member range accesses. See also LWG issue 2128.

If C is a shallow-const view, std::cbegin may return a mutable iterator. Such behavior is unexpected for some users. See also P2276 and P2278.

Example

Run this code

#include <iostream>
#include <vector>
#include <iterator>
 
int main() 
{
    std::vector<int> v = { 3, 1, 4 };
    auto vi = std::begin(v);
    std::cout << std::showpos << *vi << '\n'; 
 
    int a[] = { -5, 10, 15 };
    auto ai = std::begin(a);
    std::cout << *ai << '\n';
}

Output:

+3
-5

See also

endcend (C++11)(C++14)	returns an iterator to the end of a container or array (function template)
ranges::begin (C++20)	returns an iterator to the beginning of a range (customization point object)
ranges::cbegin (C++20)	returns an iterator to the beginning of a read-only range (customization point object)