table of contents
std::multimap::value_comp(3) | C++ Standard Libary | std::multimap::value_comp(3) |
NAME¶
std::multimap::value_comp - std::multimap::value_comp
Synopsis¶
std::multimap::value_compare value_comp() const;
Returns a function object that compares objects of type
std::multimap::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 <cassert>
#include <iostream>
#include <map>
// Example module 97 key compare function
struct ModCmp {
bool operator()(const int lhs, const int rhs) const
{
return (lhs % 97) < (rhs % 97);
}
};
int main()
{
std::multimap<int, char, ModCmp> cont;
cont = { { 1, 'a' }, { 2, 'b' }, { 3, 'c' }, { 4, 'd' }, { 5, 'e' } };
auto comp_func = cont.value_comp();
const std::pair<int, char> val = { 100, 'a' };
for (auto it : cont) {
bool before = comp_func(it, val);
bool after = comp_func(val, it);
std::cout << '(' << it.first << ',' << it.second;
if (!before && !after)
std::cout << ") equivalent to key " << val.first
<< '\n';
else if (before)
std::cout << ") goes before key " << val.first <<
'\n';
else if (after)
std::cout << ") goes after key " << val.first <<
'\n';
else
assert(0); // Cannot happen
}
}
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)
2022.07.31 | http://cppreference.com |