std::begin, std::cbegin - cppreference.com (original) (raw)
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| Defined in header <flat_map> | ||
| Defined in header <flat_set> | ||
| Defined in header <forward_list> | ||
| Defined in header <inplace_vector> | ||
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| Defined in header <string_view> | ||
| Defined in header <unordered_map> | ||
| Defined in header <unordered_set> | ||
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| 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 > constexpr auto 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) Returns c.begin(), which is typically an iterator to the beginning of the sequence represented by c.
If
Cis a standard Container, returns aC::iteratorobject.If
Cis a standard Container, returns aC::const_iteratorobject.Returns a pointer to the beginning of array.
Returns std::begin(c), with c always treated as const-qualified.
If C is a standard Container, returns a C::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()
array
c.begin()
[edit] Exceptions
specification:
noexcept(noexcept(std::begin(c)))
[edit] 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:
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; } }
[edit] Notes
The non-array overloads 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.
[edit] Example
#include #include #include int main() { std::vector 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:
[edit] See also
| | returns an iterator to the end of a container or array (function template) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns an iterator to the beginning of a range(customization point object)[edit] | | | returns an iterator to the beginning of a read-only range(customization point object)[edit] |