std::begin,std::cbegin

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Iterators library
Ranges library(C++20)
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Iterator library

Iterator concepts

indirectly_readable (C++20)
indirectly_writable (C++20)
weakly_incrementable (C++20)
incrementable (C++20)
is-integer-like is-signed-integer-like (C++20)(C++20)

sentinel_for (C++20)
sized_sentinel_for (C++20)
input_iterator (C++20)
output_iterator (C++20)
input_or_output_iterator (C++20)

forward_iterator (C++20)
bidirectional_iterator (C++20)
random_access_iterator (C++20)
contiguous_iterator (C++20)

Iterator primitives

input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag

(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)

iterator (deprecated in C++17)
iterator_traits
incrementable_traits (C++20)
indirectly_readable_traits (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)

(C++20)

(C++20)

(C++26)

reverse_iterator
make_reverse_iterator (C++14)
move_iterator (C++11)
make_move_iterator (C++11)
default_sentinel_tdefault_sentinel (C++20)(C++20)
unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)

front_insert_iterator
back_insert_iterator
inserter
insert_iterator
front_inserter
back_inserter
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)
make_const_iterator (C++23)
make_const_sentinel (C++23)

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)
rbegincrbegin (C++14)(C++14)

endcend (C++11)(C++14)
rendcrend (C++14)(C++14)

sizessize (C++17)(C++20)
empty (C++17)
data (C++17)

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Defined in header`<array>`
Defined in header`<deque>`
Defined in header`<flat_map>`
Defined in header`<flat_set>`
Defined in header`<forward_list>`
Defined in header`<inplace_vector>`
Defined in header`<iterator>`
Defined in header`<list>`
Defined in header`<map>`
Defined in header`<regex>`
Defined in header`<set>`
Defined in header`<span>`
Defined in header`<string>`
Defined in header`<string_view>`
Defined in header`<unordered_map>`
Defined in header`<unordered_set>`
Defined in header`<vector>`
template<class C> auto begin( C& c)-> decltype(c.begin());	(1)	(since C++11) (constexpr since C++17)
template<class C> auto begin(const C& c)-> decltype(c.begin());	(2)	(since C++11) (constexpr since C++17)
template<class T,std::size_t N> T* begin( T(&array)[N]);	(3)	(since C++11) (noexcept since C++14) (constexpr since C++14)
template<class C> constexprauto cbegin(const C& c)noexcept(/* see below */) -> decltype(std::begin(c));	(4)	(since C++14)

Returns an iterator to the beginning of the given range.

1,2) Returnsc.begin(), which is typically an iterator to the beginning of the sequence represented byc.

1) IfC is a standardContainer, returns aC::iterator object.

2) IfC is a standardContainer, returns aC::const_iterator object.

3) Returns a pointer to the beginning ofarray.

4) Returnsstd::begin(c), withc always treated as const-qualified.

IfC is a standardContainer, returns aC::const_iterator object.

[edit]Parameters

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

[edit]Return value

1,2)c.begin()

3)array

4)c.begin()

[edit]Exceptions

noexcept specification:

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

[edit]Overloads

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

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

Similar to the use ofswap (described inSwappable), typical use of thebegin function in generic context is an equivalent ofusing std::begin; begin(arg);, which allows both theADL-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);usingstd::end;auto end_it= end(cont);while(it!= end_it){        f(*it);++it;}}

Overloads ofbegin found byargument-dependent lookup can be used to customize the behavior ofstd::ranges::begin,std::ranges::cbegin, and other customization pointer objects depending onstd::ranges::begin.

(since C++20)

[edit]Notes

The non-array overloads exactly reflect the behavior ofC::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 alsoLWG issue 2128.

IfC is a shallow-const view,std::cbegin may return a mutable iterator. Such behavior is unexpected for some users. See alsoP2276 andP2278.

[edit]Example

Run this code

#include <iostream>#include <iterator>#include <vector> 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

[edit]See also

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