Std::begin,std::cbegin (3) Linux Manual Page

std::begin,std::cbegin – std::begin,std::cbegin

Synopsis

Defined in header<iterator>

    template <class C>
    (since C++ 11)

        auto begin(C &c) -> decltype(c.begin());
(until C++ 17)

    template <class C>
    (since C++ 17)

        constexpr auto begin(C &c) -> decltype(c.begin());

template <class C>
(since C++ 11)

    auto begin(const C &c) -> decltype(c.begin());
(until C++ 17)

    template <class C>
    (since C++ 17)

        constexpr auto begin(const C &c) -> decltype(c.begin());
(1)

    template <class T, std::size_t N>
    (since C++ 11)

        T *begin(T (&array)[N]);
(1)(until C++ 14)

    template <class T, std::size_t N>
    (since C++ 14)

        constexpr T *begin(T (&array)[N]) noexcept;
(2)

    template <class C>

    constexpr auto cbegin(const C &c) noexcept(/* see below */)(3)(since C++ 14)

        -> decltype(std::begin(c));

Returns an iterator to the beginning of the given container c or array array. These templates rely on C::begin() having a reasonable implementation.
1) Returns exactly 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.
2) Returns a pointer to the beginning of the array.
3) Returns exactly std::begin(c), with c always treated as const-qualified. If C is a standard Container, this always returns C::const_iterator.
range-begin-end.svg
This section is incomplete
Reason: an explanation why cbegin was introduced

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

3)
noexcept specification:
noexcept(noexcept(std::begin(c)))

Notes

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>.
User-defined overloads
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:
std::begin(std::initializer_list) specializes std::begin
                                                     (function template)
(C++11)
std::begin(std::valarray) specializes std::begin
                                                     (function template)
(C++11)
                                                     range-based for loop support
begin(std::filesystem::directory_iterator) (function)
end(std::filesystem::directory_iterator)
                                                     range-based for loop support
begin(std::filesystem::recursive_directory_iterator) (function)
end(std::filesystem::recursive_directory_iterator)
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;
    }
}

Example

// Run this code

#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

std::begin,std::cbegin (3) Linux Manual Page