function
<set>

std::relational operators (set)

(1)
template <class T, class Compare, class Alloc>
  bool operator== ( const set<T,Compare,Alloc>& lhs,
                    const set<T,Compare,Alloc>& rhs );
(2)
template <class T, class Compare, class Alloc>
  bool operator!= ( const set<T,Compare,Alloc>& lhs,
                    const set<T,Compare,Alloc>& rhs );
(3)
template <class T, class Compare, class Alloc>
  bool operator<  ( const set<T,Compare,Alloc>& lhs,
                    const set<T,Compare,Alloc>& rhs );
(4)
template <class T, class Compare, class Alloc>
  bool operator<= ( const set<T,Compare,Alloc>& lhs,
                    const set<T,Compare,Alloc>& rhs );
(5)
template <class T, class Compare, class Alloc>
  bool operator>  ( const set<T,Compare,Alloc>& lhs,
                    const set<T,Compare,Alloc>& rhs );
(6)
template <class T, class Compare, class Alloc>
  bool operator>= ( const set<T,Compare,Alloc>& lhs,
                    const set<T,Compare,Alloc>& rhs );
Relational operators for set
Performs the appropriate comparison operation between the set containers lhs and rhs.

Operations == and != are performed by first comparing sizes, and if they match, the elements are compared sequentially using algorithm equal, which stops at the first mismatch.

Operations <, >, <= and >= behave as if using algorithm lexicographical_compare, which compares the elements sequentially using operator< reflexively, stopping at the first mismatch.

Notice that none of these operations take into consideration the internal comparison object of neither container.

These operators are overloaded in header <set>.

Parameters

lhs, rhs
set containers (to the left- and right-hand side of the operator, respectively), having both the same template parameters (T, Compare and Alloc).

Example

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// set comparisons
#include <iostream>
#include <set>

int main ()
{
  std::set<int> foo,bar;
  foo.insert(10);
  bar.insert(20);
  bar.insert(30);
  foo.insert(40);

  // foo ({10,40}) vs bar ({20,30}):
  if (foo==bar) std::cout << "foo and bar are equal\n";
  if (foo!=bar) std::cout << "foo and bar are not equal\n";
  if (foo< bar) std::cout << "foo is less than bar\n";
  if (foo> bar) std::cout << "foo is greater than bar\n";
  if (foo<=bar) std::cout << "foo is less than or equal to bar\n";
  if (foo>=bar) std::cout << "foo is greater than or equal to bar\n";

  return 0;
}


Output:
foo and bar are not equal
foo is less than bar
foo is less than or equal to bar

Return Value

true if the condition holds, and false otherwise.

Complexity

Linear in both lhs and rhs's sizes.

Iterator validity

No changes.

Data races

Both containers, lhs and rhs, are accessed.
Concurrently accessing the elements of unmodified set objects is always safe (their elements are immutable).

Exception safety

If the type of the elements supports the appropriate operation with no-throw guarantee, the function never throws exceptions (no-throw guarantee).
In any case, the function cannot modify its arguments.

See also