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std::multiset value_comp() method

// Const version only
value_compare value_comp() const;

Returns a function object that compares objects of type value_type by comparing the first components of the pairs, same as key_comp().

Parameters

(none)

Return value

The value comparison function object.

Complexity

Constant - O(1).

Exceptions

(none)

Notes

Feature testing macro: __cpp_lib_generic_associative_lookup (for overloads (3) and (4)).

Example

Main.cpp
#include <cassert>
#include <iostream>
#include <set>

// 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::multiset<int, ModCmp> cont{1, 2, 3, 4, 5};

// Same behaviour as key_comp()
auto comp_func = cont.value_comp();

const int val = 100;

for (int key : cont) {
bool before = comp_func(key, val);
bool after = comp_func(val, key);
if (!before && !after)
std::cout << key << " equivalent to key " << val << '\n';
else if (before)
std::cout << key << " goes before key " << val << '\n';
else if (after)
std::cout << key << " goes after key " << val << '\n';
else
assert(0); // Cannot happen
}
}
Possible output
1 goes before key 100
2 goes before key 100
3 equivalent to key 100
4 goes after key 100
5 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::multiset value_comp() method

// Const version only
value_compare value_comp() const;

Returns a function object that compares objects of type value_type by comparing the first components of the pairs, same as key_comp().

Parameters

(none)

Return value

The value comparison function object.

Complexity

Constant - O(1).

Exceptions

(none)

Notes

Feature testing macro: __cpp_lib_generic_associative_lookup (for overloads (3) and (4)).

Example

Main.cpp
#include <cassert>
#include <iostream>
#include <set>

// 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::multiset<int, ModCmp> cont{1, 2, 3, 4, 5};

// Same behaviour as key_comp()
auto comp_func = cont.value_comp();

const int val = 100;

for (int key : cont) {
bool before = comp_func(key, val);
bool after = comp_func(val, key);
if (!before && !after)
std::cout << key << " equivalent to key " << val << '\n';
else if (before)
std::cout << key << " goes before key " << val << '\n';
else if (after)
std::cout << key << " goes after key " << val << '\n';
else
assert(0); // Cannot happen
}
}
Possible output
1 goes before key 100
2 goes before key 100
3 equivalent to key 100
4 goes after key 100
5 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.