C++

Reference

<functional>

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:

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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); }
};

binder2nd 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

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// 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)