deduction guides for std::basic_string

 

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Technical Specifications

 

Strings library

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Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str basic_string::operator basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)

Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::swap Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos

Non-member functions operator+ swap(std::basic_string) operator""s (C++14) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>= Numeric conversion (C++11) stoistolstoll stoulstoull stofstodstold to_string to_wstring Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string>hash<std::u8string> (C++11)(C++11)(C++11)(C++11)(C++20) hash<std::pmr::string>hash<std::pmr::wstring>hash<std::pmr::u32string>hash<std::pmr::u16string>hash<std::pmr::u8string> (C++20)(C++20)(C++20)(C++20)(C++20) Deduction guides(C++17)

 

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 std::iterator_traits<InputIt>::value_type,                 std::char_traits<typename std::iterator_traits<InputIt>::value_type>,                 Alloc>;	(1)	(since C++17)
template<class CharT,          class Traits,          class Alloc = std::allocator<CharT>> explicit basic_string(std::basic_string_view<CharT, Traits>, const Alloc& = Alloc()) -> basic_string<CharT, Traits, Alloc>;	(2)	(since C++17)
template<class CharT,          class Traits,          class Alloc = std::allocator<CharT>>> basic_string(std::basic_string_view<CharT, Traits>, typename /*see below*/::size_type,              typename /*see below*/::size_type, const Alloc& = Alloc())     -> basic_string<CharT, Traits, Alloc>;	(3)	(since C++17)

1) This deduction guide is provided for std::basic_string to allow deduction from an iterator range. This overload only participates in overload resolution 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 only participate in overload resolution if Alloc satisfies Allocator.

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 deduction.

Defect reports

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

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

Example

Run this code

#include <string>
#include <vector>
int main() {
   std::vector<char> v = {'a', 'b', 'c'};
   std::basic_string s(v.begin(), v.end()); // uses explicit deduction guide
}