std::map<Key,T,Compare,Allocator>::value_comp

 

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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

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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)

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std::map::value_compare value_comp()const;

Returns a function object that compares objects of type std::map::value_type (key-value pairs) by using key_comp to compare the first components of the pairs.

Parameters

(none)

Return value

The value comparison function object.

Complexity

Constant.

Example

Run this code

#include <iostream>#include <map>#include <utility>   // Example module 97 key compare functionstruct ModCmp {bool operator()(int lhs, int rhs)const{return(lhs %97)<(rhs %97);}};   int main(){std::map<int, char, ModCmp> cont; cont ={{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}, {5, 'e'}};   auto comp_func = cont.value_comp();   for(conststd::pair<int, char> val ={100, 'a'};auto it : cont){constbool before = comp_func(it, val);constbool after = comp_func(val, it);   std::cout<<'('<< it.first<<','<< it.second<<") ";if(!before &&!after)std::cout<<"equivalent to key ("<< val.first<<")\n";elseif(before)std::cout<<"goes before key ("<< val.first<<")\n";elseif(after)std::cout<<"goes after key ("<< val.first<<")\n";elsestd::unreachable();}}

Output:

(1,a) goes before key (100) (2,b) goes before key (100) (3,c) equivalent to key (100) (4,d) goes after key (100) (5,e) goes after key (100)

See also

key_comp

returns the function that compares keys (public member function)