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std::begin

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< cpp‎ | iterator
Revision as of 18:18, 4 June 2014 by Cubbi (Talk | contribs)

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

Returns an iterator to the beginning of the given container c or array array.

1) Returns a possibly const-qualified iterator to the beginning of the container c.
2) Returns a pointer to the beginning of the array array.
3) Returns a const-qualified iterator to the beginning of the container c.

range-begin-end.svg

Contents

Parameters

c - a container with a begin method
array - an array of arbitrary type

Return value

An iterator to the beginning of c or array

Exceptions

2)
noexcept specification:  
noexcept
  
(since C++14)
3)
noexcept specification:  
noexcept(noexcept(std::begin(c)))

Notes

In addition to being included in <iterator>, std::begin is guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>, <string>, <unordered_map>, <unordered_set>, and <vector>.

User-defined overloads

Custom overloads of std::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:

specializes std::begin
(function template) [edit]
specializes std::begin
(function template) [edit]

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 lets 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;
    }
}

Example

#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

See also

(C++11)(C++14)
returns an iterator to the end of a container or array
(function) [edit]