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 .
1) If C is a standard Container , returns a C::iterator object. 2) If C is a standard Container , returns a C::const_iterator object. 3) Returns a pointer to the beginning of array . 4) Returns std :: begin ( c ) , with c always treated as const-qualified. If C is a standard Container , returns a C::const_iterator object.| c | - | a container or view with a begin member function |
| array | - | an array of arbitrary type |
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.
templatetypename 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 other customization pointer objects depending on std :: ranges:: begin .
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.
#include #include #include int main() { std::vectorint> 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'; }