学步园

1.unary_function

即一元函数

在vs2008自带的STL库中，它的定义如下

template <class Arg, class Result>
  struct unary_function {
    typedef Arg argument_type;
    typedef Result result_type;
  };

为什么叫一元函数呢？看一下它的使用方法就清楚了

struct IsOdd : public unary_function<int,bool>

{
  bool operator() (int number)

  {

      return (number%2==1);

  }
};

就是说,unary_function的子类的函数对象只接收一个参数

bool operator() (int number)中的int number

"this operator() member function takes one single parameter"

unary_function测试代码如下

#include <iostream><br /> #include <functional><br /> using namespace std;<br /> struct IsOdd : public unary_function<int,bool> {<br /> bool operator() (int number) {return (number%2==1);}<br /> };<br /> void TestUnaryFunc()<br /> {<br /> IsOdd IsOdd_object;<br /> IsOdd::argument_type input;<br /> IsOdd::result_type result;<br /> cout << "Please enter a number: ";<br /> cin >> input;<br /> result = IsOdd_object (input);<br /> cout << "Number " << input << " is " << (result?"odd":"even") << "./n";<br /> }

2.binary_function

二元函数对象,由上易知这个函数对象有两个参数

见它的定义

template<class _Arg1,
    class _Arg2,
    class _Result>
    struct binary_function
    {    // base class for binary functions
    typedef _Arg1 first_argument_type;
    typedef _Arg2 second_argument_type;
    typedef _Result result_type;
    };

“In the case of binary function objects, this operator() member function takes two parameters.”

TestBinaryFunc()测试代码如下

//TestBinaryFunc.cpp<br /> //这段代码源于cplusplus<br /> #include <iostream><br /> #include <functional><br /> using namespace std;<br /> struct Compare : public binary_function<int,int,bool> {<br /> bool operator() (int a, int b) {return (a==b);}<br /> };<br /> void TestBinaryFunc()<br /> {<br /> Compare Compare_object;<br /> Compare::first_argument_type input1;<br /> Compare::second_argument_type input2;<br /> Compare::result_type result;<br /> cout << "Please enter first number: ";<br /> cin >> input1;<br /> cout << "Please enter second number: ";<br /> cin >> input2;<br /> result = Compare_object (input1,input2);<br /> cout << "Numbers " << input1 << " and " << input2;<br /> if (result)<br /> cout << " are equal./n";<br /> else<br /> cout << " are not equal./n";<br /> }

3.bind1st

看完了1和2，bind1st就很容易理解了。它先利用binary_function,先绑定一个

参数,然后像使用一元函数对象那样使用binary_function

以下是bind1st的部分代码

  binder1st(const _Fn2& _Func,
        const typename _Fn2::first_argument_type& _Left)
        : op(_Func), value(_Left)
        {    // construct from functor and left operand
        }

//_Left绑定了一个参数

//_Func一个二元函数对象

//这样就实现了像使用一元函数对象那样使用二元函数对象了

    result_type operator()(const argument_type& _Right) const
        {    // apply functor to operands
        return (op(value, _Right));
        }

bind1st测试代码如下

//TestBind1st.cpp<br /> #include <iostream><br /> #include <functional><br /> #include <algorithm><br /> using namespace std;<br /> void TestBind1st()<br /> {<br /> int numbers[] = {10,20,30,40,50,10};<br /> int cx;<br /> cx = count_if (numbers, numbers+6, bind1st(equal_to<int>(),10) );<br /> cout << "There are " << cx << " elements that are equal to 10./n";<br /> }

TestBind2nd就好理解了。它绑定了二元函数对象的第二个参数