Przejdź do głównej zawartości

std::map key_comp() method

// Const version only
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 - O(1).

Exceptions

(none)

Example

Main.cpp
#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::map<int, char, ModCmp> cont;
cont = { { 1, 'a' }, { 2, 'b' }, { 3, 'c' }, { 4, 'd' }, { 5, 'e' } };

auto comp_func = cont.key_comp();

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

std::cout << '(' << 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
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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::map key_comp() method

// Const version only
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 - O(1).

Exceptions

(none)

Example

Main.cpp
#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::map<int, char, ModCmp> cont;
cont = { { 1, 'a' }, { 2, 'b' }, { 3, 'c' }, { 4, 'd' }, { 5, 'e' } };

auto comp_func = cont.key_comp();

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

std::cout << '(' << 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
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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.