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:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
| 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); } };
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
| // 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)