class template
<functional>

std::binder1st

template <class Operation> class binder1st;
Generate function object class with 1st parameter bound
Generates an unary function object class from the binary object class Operation by binding its first parameter to a fixed value.

binder1st is generally used as a type. The function bind1st (also defined in header <functional>) can be used to directly construct an object of this type.

binder1st 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 binder1st
  : public unary_function <typename Operation::second_argument_type,
                           typename Operation::result_type>
{
protected:
  Operation op;
  typename Operation::first_argument_type value;
public:
  binder1st ( const Operation& x,
              const typename Operation::first_argument_type& y) : op (x), value(y) {}
  typename Operation::result_type
    operator() (const typename Operation::second_argument_type& x) const
    { return op(value,x); }
};


binder1st 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 first 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 first argument bound to a specific value.

Example

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// binder1st example
#include <iostream>
#include <functional>
#include <algorithm>
using namespace std;

int main () {
  binder1st < equal_to<int> > equal_to_10 (equal_to<int>(),10);
  int numbers[] = {10,20,30,40,50,10};
  int cx;
  cx = count_if (numbers,numbers+6,equal_to_10);
  cout << "There are " << cx << " elements equal to 10.\n";
  return 0;
}


Output:

There are 2 elements equal to 10.

See also

bind1st
Return function object with first parameter bound (function template )
binder2nd
Generate function object class with 2nd parameter bound (class template )
unary_function
Unary function object base class (class template )
binary_function
Binary function object base class (class template )

C++