Defined in header <iterator> | ||
---|---|---|
(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 container c
or array array
. These templates rely on C::begin()
having a reasonable implementation.
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.array
.std::begin(c)
, with c
always treated as const-qualified. If C
is a standard Container, this always returns C::const_iterator
.c | - | a container with a begin method |
array | - | an array of arbitrary type |
An iterator to the beginning of c
or array
.
noexcept
specification: noexcept(noexcept(std::begin(c)))
In addition to being included in <iterator>
, std::begin
and std::cbegin
are guaranteed to become available if any of the following headers are included: <array>
, <deque>
, <forward_list>
, <list>
, <map>
, <regex>
, <set>
, <span>
(since C++20), <string>
, <string_view>
(since C++17), <unordered_map>
, <unordered_set>
, and <vector>
.
Custom overloads of begin
may be provided for classes that do not expose a suitable begin()
member function, yet can be iterated. The following overloads are already provided by the standard library:
(C++11) | specializes std::begin (function template) |
(C++11) | specializes std::begin (function template) |
range-based for loop support (function) |
|
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; } }
#include <iostream> #include <vector> #include <iterator> int main() { std::vector<int> v = { 3, 1, 4 }; auto vi = std::begin(v); std::cout << *vi << '\n'; int a[] = { -5, 10, 15 }; auto ai = std::begin(a); std::cout << *ai << '\n'; }
Output:
3 -5
(C++11)(C++14) | returns an iterator to the end of a container or array (function template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/iterator/begin