NAME

std::begin,std::cbegin - std::begin,std::cbegin

Synopsis

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>
(since
template< class C > C++11)
auto begin( C& c ) -> decltype(c.begin()); (until
C++17)
template< class C > (since
constexpr auto begin( C& c ) -> C++17)
decltype(c.begin());
(since
template< class C > C++11)
auto begin( const C& c ) -> decltype(c.begin()); (until
C++17)
template< class C > (since
constexpr auto begin( const C& c ) -> (1) C++17)
decltype(c.begin());
(since
template< class T, std::size_t N > C++11)
T* begin( T (&array)[N] ); (1) (until
C++14)
template< class T, std::size_t N > (since
constexpr T* begin( T (&array)[N] ) noexcept; (2) C++14)
template< class C >

constexpr auto cbegin( const C& c ) noexcept(/* (3) (since
see below */) C++14)

-> decltype(std::begin(c));

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.

range-begin-end.svg

Parameters

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

Return value

An iterator to the beginning 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) overloads std::begin
(C++11) (function template)
std::begin(std::valarray) overloads std::begin
(C++11) (function template)
begin(std::filesystem::directory_iterator) range-based for loop support
end(std::filesystem::directory_iterator) (function)
(C++17)
begin(std::filesystem::recursive_directory_iterator) range-based for loop support
end(std::filesystem::recursive_directory_iterator) (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 (since C++20)
other customization pointer objects depending on std::ranges::begin.

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