NAME¶

std::flat_map::value_comp - std::flat_map::value_comp

Synopsis¶

std::flat_map::value_compare value_comp() const; (since C++23)

Returns a function object that compares objects of type std::flat_map::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 <iostream>
#include <flat_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::flat_map<int, char, ModCmp> cont;
cont = {{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}, {5, 'e'}};

auto comp_func = cont.value_comp();

for (const std::pair<int, char> val = {100, 'a'}; auto it : cont)
{
const bool before = comp_func(it, val);
const 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
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¶

key_comp returns the function that compares keys
(public member function)