仿函数相关

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#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>

template< class iterator, class predicate, class doer>
    void for_each_if( iterator itFirst, iterator itLast, predicate pred, doer do_it)
{
    while ( itFirst != itLast)
    {
        if ( pred( *itFirst)) do_it( *itFirst);
        ++itFirst;
    }
}

void print( int i) { std::cout << i << " "; }

int _tmain(int argc, _TCHAR* argv[])
{

    int aNumbers[] = { 10, 5, 89, 9, 30, -2, -8, 7, 33, 25, 30, 76, 0, 2};
    int nCount = sizeof( aNumbers) / sizeof( aNumbers[ 0]);

    // a < b
    std::cout << "\nNumbers less than 30: ";
    for_each_if( aNumbers, aNumbers + nCount,
        std::bind2nd( std::less< int>(), 30), print);
    std::cout << "\nNumbers bigger than 30: ";
    // a > b
    for_each_if( aNumbers, aNumbers + nCount,
        std::bind1st( std::less< int>(), 30), print);
    std::cout << "\nNumbers less or equal than 30: ";
    // a <= b      <=>     !(a > b)
    for_each_if( aNumbers, aNumbers + nCount,
        std::not1( std::bind1st( std::less< int>(), 30)), print);
    std::cout << "\nNumbers bigger or equal than 30: ";
    // a >= b      <=>     !(a < b)
    for_each_if( aNumbers, aNumbers + nCount,
        std::not1( std::bind2nd( std::less< int>(), 30)), print);
    return 0;

}

call operator()和构造函数以及仿函数(仿函数不是函数，而是一个类，这个类重载了()操作符)
class A
{
public：
    A()
    {
      m_a = 0;
    }
    A(int args)
    {
      m_a = args;
    }
    bool operator()(int a)
    {
   std::cout << a;
        return false;
    }
private:
   int m_a;
};
就这个类来说：
call operator() 的方法:
1 A a(12);//call con
   a(13);//call ()
   a.operator()(13);//call ()
2 A* p_a = new A;
p_a(13);//错的
(*p_a)(13);//call ()
p_a->operator()(13);//call ()

struct A
{
   int n_;
   int add(int args){return n_+= args;}
   int test(){return n_;}
};
A a(10);
int n1 = mem_fun_ref(&A::test)(a);
int n2 = mem_fun_ref(&A::add)(a,100);//重载() 时候用到得参数，奇特吧

直接上代码是最直接的，胜过很多的文字

仿函数就是实现了operator() ，没有其他很特别的，类似上面的，一般函数如print 调用直接是函数名，仿函数需加上括号

代码多看多想多写。。。

仿函数 相关

仿函数相关