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deductiongu...basic_string(3)  C++ Standard Libary deductiongu...basic_string(3)

NAME
     deductionguidesforstd::basic_string - deductionguidesforstd::basic_string

Synopsis
	Defined in header <string>
	template< class InputIt, class Alloc = std::allocator<

				     typename
	std::iterator_traits<InputIt>::value_type> >
	basic_string( InputIt, InputIt, Alloc = Alloc() )
	    ->	basic_string<typename					     (1)
     (since C++17)
	std::iterator_traits<InputIt>::value_type,
			    std::char_traits<

				typename
	std::iterator_traits<InputIt>::value_type>, Alloc>;
	template< class CharT,

		  class Traits,
		  class Alloc = std::allocator<CharT>  >		     (2)
     (since C++17)
	explicit basic_string( std::basic_string_view<CharT, Traits>,
	const Alloc& = Alloc() )

	    -> basic_string<CharT, Traits, Alloc>;
	template< class CharT,

		  class Traits,
		  class Alloc = std::allocator<CharT>> >
	basic_string(  std::basic_string_view<CharT,  Traits>,		     (3)
     (since C++17)
		      typename /* see below */::size_type,
		      typename /* see below */::size_type,
		      const Alloc& = Alloc() )

	    -> basic_string<CharT, Traits, Alloc>;
	template< ranges::input_range R,

		  class Alloc = std::allocator<ranges::range_value_t<R>> >
	basic_string( std::from_range_t, R&&, Alloc = Alloc()  )	     (4)
     (since C++23)
	    -> basic_string<ranges::range_value_t<R>,

			       std::char_traits<ranges::range_value_t<R>>,
	Alloc>;

	1)  This  deduction guide is provided for std::basic_string to allow de-
     duction from an
	iterator range. This overload participates in overload	resolution  only
     if InputIt
	satisfies LegacyInputIterator and Alloc satisfies Allocator.
	2,3)  These deduction guides are provided for std::basic_string to allow
     deduction
	from a std::basic_string_view.	The  size_type	parameter  type  in  (3)
     refers to the
	size_type  member type of the type deduced by the deduction guide. These
     overloads
	participate in overload resolution only if Alloc satisfies Allocator.
	4) This deduction guide is provided for std::basic_string to  allow  de-
     duction from a
	std::from_range_t tag and an input_range.

	Note:  the  extent  to which the library determines that a type does not
     satisfy
	LegacyInputIterator is unspecified, except that as  a  minimum	integral
     types do not
	qualify  as input iterators. Likewise, the extent to which it determines
     that a type
	does not satisfy Allocator is unspecified, except that as a minimum  the
     member type
	Alloc::value_type must exist and the expression
	std::declval<Alloc&>().allocate(std::size_t{})	must be well-formed when
     treated as
	an unevaluated operand.

Notes
	Guides (2,3) are needed because the std::basic_string constructors for
	std::basic_string_views are made templates to avoid causing  ambiguities
     in existing
	code,  and those templates do not support class template argument deduc-
     tion.

Notes
	    Feature-test macro	     Value    Std		    Feature
	__cpp_lib_containers_ranges 202202L  (C++23)  Ranges-aware  construction
     and insertion;
						    overload (4)

Example
     // Run this code

      #include <cassert>
      #include <string>
      #include <vector>

      int main()
      {
	  std::vector<char> v = {'a', 'b', 'c'};
	  std::basic_string s1(v.begin(), v.end()); // uses deduction guide (1)
	  assert(s1 == "abc");

      #if __cpp_lib_containers_ranges >= 202202L
	  std::vector<wchar_t> v4{0x43, 43, 053, 0x32, 0x33};
	  std::basic_string s4(std::from_range, v4); // uses deduction guide (4)
	  assert(s4 == L"C++23");
      #endif
      }

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to		Behavior as published		    Cor-
     rect behavior
	LWG  3075  C++17      deduction from basic_string_view was	     de-
     duction guides
			    unsupported (exacerbated by LWG issue 2946)    added

http://cppreference.com 	   2024.06.10	   deductiongu...basic_string(3)
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