From cppreference.com
std::multimap::value_comparevalue_comp()const;Returns a function object that compares objects of type std::multimap::
(key-value pairs) by using
to compare the first components of the pairs.
Return value
The value comparison function object.
Complexity
Constant.
Example
Run this code
#include<iostream>#include<map>#include<utility>// Example module 97 key compare functionstructModCmp{booloperator()(intlhs,intrhs)const{return(lhs%97)<(rhs%97);}};intmain(){std::multimap<int,char,ModCmp>cont;cont={{1,'a'},{2,'b'},{3,'c'},{4,'d'},{5,'e'}};autocomp_func=cont.value_comp();for(conststd::pair<int,char>val={100,'a'};autoit:cont){constboolbefore=comp_func(it,val);constboolafter=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
returns the function that compares keys
(public member function)