class template
std::less
<functional>
template <class T> struct less;
Function object class for less-than inequality comparison
This class defines function objects for the
"less than" inequality comparison operation.
Generically,
function objects are instances of a class with member function
operator() defined. This member function allows the object to be used with the same syntax as a regular function call, and therefore it can be used in templates instead of a pointer to a function.
less has its
operator() member defined such that it returns
true if its first argument compares lower than the second one using
operator<, and
false otherwise.
This class is derived from
binary_function and is defined as:
1 2 3 4
|
template <class T> struct less : binary_function <T,T,bool> {
bool operator() (const T& x, const T& y) const
{return x<y;}
};
|
Objects of this class can be used with some standard algorithms such as
sort,
merge or
lower_bound.
Members
- bool operator() (const T& x, const T& y)
- Member function returning the result of the comparison x<y.
Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
|
// less example
#include <iostream>
#include <functional>
#include <algorithm>
using namespace std;
int main () {
int foo[]={10,20,5,15,25};
int bar[]={15,10,20};
sort (foo, foo+5, less<int>() ); // 5 10 15 20 25
sort (bar, bar+3, less<int>() ); // 10 15 20
if ( includes ( foo, foo+5, bar, bar+3, less<int>() ) )
cout << "foo includes bar.\n";
return 0;
}
|
Output:
See also
- equal_to
- Function object class for equality comparison (class template
)
- not_equal_to
- Function object class for non-equality comparison (class template
)
- greater
- Function object class for greater-than inequality comparison (class template
)
- greater_equal
- Function object class for greater-than-or-equal-to comparison (class template
)
- less_equal
- Function object class for less-than-or-equal-to comparison (class template
)
- binary_function
- Binary function object base class (class template)