std::set::key_comp

key_compare key_comp() const;

Return comparison object

Returns a copy of the comparison object used by the container.

By default, this is a less object, which returns the same as operator<.

This object determines the order of the elements in the container: it is a function pointer or a function object that takes two arguments of the same type as the container elements, and returns true if the first argument is considered to go before the second in the strict weak ordering it defines, and false otherwise.

Two elements of a set are considered equivalent if key_comp returns false reflexively (i.e., no matter the order in which the elements are passed as arguments).

In set containers, the keys to sort the elements are the values themselves, therefore key_comp and its sibling member function value_comp are equivalent.

Parameters

none

Return value

The comparison object.
Member type key_compare is the type of the comparison object associated to the container, defined in set as an alias of its second template parameter (Compare).

Example

// set::key_comp
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  int highest;

  std::set<int>::key_compare mycomp = myset.key_comp();

  for (int i=0; i<=5; i++) myset.insert(i);

  std::cout << "myset contains:";

  highest=*myset.rbegin();
  std::set<int>::iterator it=myset.begin();
  do {
    std::cout << ' ' << *it;
  } while ( mycomp(*(++it),highest) );

  std::cout << '\n';

  return 0;
}

Output:

myset contains: 0 1 2 3 4

Complexity

Constant.

Iterator validity

No changes.

Data races

The container is accessed.
Concurrently accessing the elements of a set is safe.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.

member functions

non-member overloads