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.
(none).
The value comparison function object.
Constant.
#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
| returns the function that compares keys (public member function) |
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