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deductiongu...basic_string(3) C++ Standard Libarydeductiongu...basic_string(3) NAME deductionguidesforstd::basic_string - deductionguidesforstd::ba- sic_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 deduction 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 Alloca- tor. 4) This deduction guide is provided for std::basic_string to allow deduction 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 inte- gral types do not qualify as input iterators. Likewise, the extent to which it deter- mines 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 ambigui- ties in existing code, and those templates do not support class template argument de- duction. Notes Feature-test macro Value Std Feature __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construc- tion 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 Correct behavior LWG 3075 C++17 deduction from basic_string_view was deduction guides unsupported (exacerbated by LWG issue 2946) added http://cppreference.com 2024.06.10 deductiongu...basic_string(3)
NAME | Synopsis | Notes | Notes | Example
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