class template
<functional>
std::binder2nd
template <class Operation> class binder2nd;
Generate function object class with 2nd parameter bound
Generates an unary function object class from the binary object class
Operation by binding its second parameter to a fixed value.
binder2nd is generally used as a type. The function
bind2nd (also defined in header
<functional>) can be used to directly construct an object of this type.
binder2nd is constructed using a
binary function object as argument. A copy of this object is used by its member
operator() to generate a result from its parameter and the fixed value set on construction.
This class is derived from
unary_function and is typically defined as:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
template <class Operation> class binder2nd
: public unary_function <typename Operation::first_argument_type,
typename Operation::result_type>
{
protected:
Operation op;
typename Operation::second_argument_type value;
public:
binder2nd ( const Operation& x,
const typename Operation::second_argument_type& y) : op (x), value(y) {}
typename Operation::result_type
operator() (const typename Operation::first_argument_type& x) const
{ return op(x,value); }
};
class is specifically designed to bind function objects (
operations) derived from
binary_function (it requires member
first_argument_type and
second_argument_type).
Members
- constructor
- Constructs an unary function object class from a binary function object by binding its second argument to a value.
- operator()
- Member function taking a single parameter and returning the result of calling the binary function object used at construction with its second argument bound to a specific value.
Example
1
2
3
4
5
6
7
8
9
10
11
12
13
14
// binder2nd example
#include <iostream>
#include <functional>
#include <algorithm>
using namespace std;
int main () {
binder2nd < less<int> > IsNegative (less<int>(),0);
int numbers[] = {10,-20,-30,40,-50};
int cx;
cx = count_if (numbers,numbers+5,IsNegative);
cout << "There are " << cx << " negative elements.\n";
return 0;
}
Output:
There are 3 negative elements.
See also
- bind2nd
- Return function object with second parameter bound (function template)
- binder1st
- Generate function object class with 1st parameter bound (class template)
- unary_function
- Unary function object base class (class template)
- binary_function
- Binary function object base class (class template)