std::begin,std::cbegin(3)

NAME
std::begin,std::cbegin - std::begin,std::cbegin

Synopsis
   Defined in header <array>
   Defined in header <deque>
   Defined in header <forward_list>
   Defined in header <iterator>
   Defined in header <list>
   Defined in header <map>
   Defined in header <regex>
   Defined in header <set>
   Defined in header <span> (since
                        C++20)
   Defined in header <string>
   Defined in header <string_view> (since
                        C++17)
   Defined in header <unordered_map>
   Defined in header <unordered_set>
   Defined in header <vector>
                        (since
   template< class C > C++11)
   auto begin( C& c ) -> decltype(c.begin()); (until
                        C++17)
   template< class C > (since
   constexpr auto begin( C& c ) -> C++17)
   decltype(c.begin());
                        (since
   template< class C > C++11)
   auto begin( const C& c ) -> decltype(c.begin()); (until
                        C++17)
   template< class C > (since
   constexpr auto begin( const C& c ) -> (1) C++17)
   decltype(c.begin());
                        (since
   template< class T, std::size_t N > C++11)
   T* begin( T (&array)[N] ); (1) (until
                        C++14)
   template< class T, std::size_t N > (since
   constexpr T* begin( T (&array)[N] ) noexcept; (2) C++14)
   template< class C >
   constexpr auto cbegin( const C& c ) noexcept(/* (3) (since
   see below */) C++14)
   -> decltype(std::begin(c));
   Returns an iterator to the beginning of the given range.
   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

Parameters
   c - a container or view with a begin member function
   array - an array of arbitrary type

Return value
   An iterator to the beginning the range.

Exceptions
   3)
   noexcept specification:
   noexcept(noexcept(std::begin(c)))
  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:
   std::begin(std::initializer_list) overloads std::begin
   (C++11) (function template)
   std::begin(std::valarray) overloads std::begin
   (C++11) (function template)
   begin(std::filesystem::directory_iterator) range-based for loop support
   end(std::filesystem::directory_iterator) (function)
   (C++17)
   begin(std::filesystem::recursive_directory_iterator) range-based for loop support
   end(std::filesystem::recursive_directory_iterator) (function)
   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;
     }
 }
   Overloads of begin found by argument-dependent lookup can be used to
   customize the behavior of std::ranges::begin, std::ranges::cbegin, and (since C++20)
   other customization pointer objects depending on std::ranges::begin.

Notes
   (1,3) 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.

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 << std::showpos << *vi << '\n';
     int a[] = { -5, 10, 15 };
     auto ai = std::begin(a);
     std::cout << *ai << '\n';
 }

Output:
 +3
 -5

See also
   end
   cend returns an iterator to the end of a container or array
   (C++11) (function template)
   (C++14)
   ranges::begin returns an iterator to the beginning of a range
   (C++20) (customization point object)
   ranges::cbegin returns an iterator to the beginning of a read-only range
   (C++20) (customization point object)