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Showing content from http://en.cppreference.com/w/cpp/language/../iterator/begin.html below:

std::begin, std::cbegin - cppreference.com

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.

1)

C

is a standard

Container

, returns a

C::iterator

object.

2)

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.

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()

3) array

4) c.begin()

[edit] Exceptions 4) noexcept

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 <iostream>
#include <iterator>
#include <vector>
 
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:

[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]

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