NAME¶

std::map::key_comp - std::map::key_comp

Synopsis¶

key_compare key_comp() const;

Returns the function object that compares the keys, which is a copy of this
container's constructor argument comp.

Parameters¶

(none)

Return value¶

The key comparison function object.

Complexity¶

Constant.

Example¶

// Run this code

#include <iostream>
#include <map>
#include <utility>

// Example module 97 key compare function
struct 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.key_comp();

for (const auto it : cont)
{
const bool before = comp_func(it.first, 100);
const bool after = comp_func(100, it.first);

std::cout << "Key (" << it.first << ',' << it.second << ") ";
if (!before && !after)
std::cout << "equivalent to key (100)\n";
else if (before)
std::cout << "goes before key (100)\n";
else if (after)
std::cout << "goes after key (100)\n";
else
std::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¶

value_comp returns the function that compares keys in objects of type value_type
(public member function)