deduction guides for std::map

 

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Containers library

node-handle (C++17)

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array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (C++26)

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list

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set

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map

multimap

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unordered_set (C++11)

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unordered_map (C++11)

unordered_multimap (C++11)

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stack

queue

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flat_map (C++23)

flat_multimap (C++23)

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span (C++20)

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std::map

Member functions

map::map map::~map               map::operator= map::get_allocator

Element access map::at map::operator[] Iterators map::beginmap::cbegin (C++11) map::endmap::cend (C++11) map::rbeginmap::crbegin (C++11)      map::rendmap::crend (C++11) Capacity map::size map::max_size map::empty Observers map::key_comp map::value_comp Modifiers map::clear map::insert map::erase map::swap map::extract (C++17) map::merge (C++17) map::insert_range (C++23) map::insert_or_assign (C++17) map::emplace (C++11) map::emplace_hint (C++11) map::try_emplace (C++17) Lookup map::count map::find map::contains (C++20) map::equal_range map::lower_bound map::upper_bound

Non-member functions

operator==operator<=> (C++20) std::swap(std::map) erase_if(std::map) (C++20)   operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)

Deduction guides(C++17)

 

Defined in header <map>
template<class InputIt,           class Comp =std::less</*iter-key-t*/<InputIt>>,           class Alloc =std::allocator</*iter-to-alloc-t*/<InputIt>>> map( InputIt, InputIt, Comp = Comp(), Alloc = Alloc())     -> map</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>, Comp, Alloc>;	(1)	(since C++17)
template<class Key,           class T,           class Comp =std::less<Key>,           class Alloc =std::allocator<std::pair<const Key, T>>> map(std::initializer_list<std::pair<Key, T>>, Comp = Comp(), Alloc = Alloc())     -> map<Key, T, Comp, Alloc>;	(2)	(since C++17)
template<class InputIt, class Alloc > map( InputIt, InputIt, Alloc )     -> map</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>,            std::less</*iter-key-t*/<InputIt>>, Alloc>;	(3)	(since C++17)
template<class Key, class T, class Alloc > map(std::initializer_list<std::pair<Key, T>>, Alloc )     -> map<Key, T, std::less<Key>, Alloc>;	(4)	(since C++17)
template<ranges::input_range R, class Compare =std::less</*range-key-t*/<R>,           class Alloc =std::allocator</*range-to-alloc-t*/<R>>> map(std::from_range_t, R&&, Compare = Compare(), Alloc = Alloc())     -> map</*range-key-t*/<R>, range_mapped_t<R>, Compare, Alloc>;	(5)	(since C++23)
template<ranges::input_range R, class Alloc > map(std::from_range_t, R&&, Alloc )     -> map</*range-key-t*/<R>, range_mapped_t<R>,        map std::less</*range-key-t*/<R>>, Alloc>;	(6)	(since C++23)
Exposition-only helper type aliases
template<class InputIt > using/*iter-val-t*/=     typenamestd::iterator_traits<InputIt>::value_type;		(exposition only*)
template<class InputIt > using/*iter-key-t*/=     std::remove_const_t<std::tuple_element_t<0, /*iter-val-t*/<InputIt>>>;		(exposition only*)
template<class InputIt > using/*iter-mapped-t*/=     std::tuple_element_t<1, /*iter-val-t*/<InputIt>>;		(exposition only*)
template<class InputIt > using/*iter-to-alloc-t*/=     std::pair<std::add_const_t<tuple_element_t<0, /*iter-val-t*/<InputIt>>>,               std::tuple_element_t<1, /*iter-val-t*/<InputIt>>>;		(exposition only*)
template<ranges::input_range Range > using/*range-key-t*/=     std::remove_const_t<typenameranges::range_value_t<Range>::first_type>;		(since C++23) (exposition only*)
template<ranges::input_range Range > using/*range-mapped-t*/=     typenameranges::range_value_t<Range>::second_type;		(since C++23) (exposition only*)
template<ranges::input_range Range > using/*range-to-alloc-t*/=     std::pair<std::add_const_t<typenameranges::range_value_t<Range>::first_type>,               typenameranges::range_value_t<Range>::second_type>;		(since C++23) (exposition only*)

1-4) These deduction guides are provided for map to allow deduction from an iterator range (overloads (1,3)) and std::initializer_list (overloads (2,4)).

5,6) These deduction guides are provided for map to allow deduction from a std::from_range_t tag and an input_range.

These overloads participate in overload resolution only if InputIt satisfies LegacyInputIterator, Alloc satisfies Allocator, and Comp does not satisfy 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

Feature-test macro	Value	Std	Feature
__cpp_lib_containers_ranges	202202L	(C++23)	Ranges-aware construction and insertion; overload (5,6)

Example

Run this code

#include <map>   int main(){// std::map m1 = {{"foo", 1}, {"bar", 2}};// Error: braced-init-list has no type; cannot deduce// pair<Key, T> from {"foo", 1} or {"bar", 2}   std::map m1 ={std::pair{"foo", 2}, {"bar", 3}};// guide #2std::map m2(m1.begin(), m1.end());// guide #1}

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 3025	C++17	initializer-list guides (2,4) take std::pair<const Key, T>	use std::pair<Key, T>