函數(shù)指針實(shí)在是個(gè)討厭的東西，說(shuō)實(shí)話，我很討厭他的語(yǔ)法，非常丑陋，而且有很多局限性，起碼不能保有數(shù)據(jù)，函數(shù)對(duì)象是一個(gè)替換函數(shù)指針的好東東，通過(guò)重載operator()操作符，可以實(shí)現(xiàn)與函數(shù)指針幾乎完全一致的功能。最近在看《C++必知必會(huì)》，里面講到用函數(shù)對(duì)象替代函數(shù)指針，還有例子，覺(jué)得很好，貼出來(lái)，供兄弟們一起參考研究。

下面的代碼并不復(fù)雜，先定義了一個(gè)基類函數(shù)對(duì)象Action，Button類帶有一個(gè)Action的指針，作為其回調(diào)函數(shù)，在setAction中設(shè)置回調(diào)。由于Action是一個(gè)基類，所有繼承了Action的繼承類如PlayMusic都可以被Button調(diào)用，而且不需要改變接口，這個(gè)比起函數(shù)指針作回調(diào)來(lái)說(shuō)，簡(jiǎn)單了很多，也清晰很多。

下面是代碼：

#include <iostream>
#include <string>
#include <stdlib.h>

using namespace std;

class Action
{
public:
    virtual ~Action() = 0;
    virtual void operator()() = 0;
    virtual Action *clone() const = 0;
};

Action::~Action()
{ cout << "::~Action()" << endl; }

void Action::operator()()
{
    cout << "1111111111" << endl;
}

class Button
{
public:
    Button( const string &label )
        : m_label( label ), m_action( 0 ) {}
    ~Button()
    {
        if( m_action )
        {
            delete m_action;
            m_action = NULL;
        }   
    }
    void setAction( const Action *newAction )
    {
        Action *tmp = newAction->clone();
        delete m_action;
        m_action = tmp;
    }
    void onClick() const
    {
        if( m_action )
            ( *m_action )();
    }

private:
    string m_label;
    Action *m_action;
};

class PlayMusic : public Action
{
public:
    PlayMusic( const string &songFile )
        :m_song( songFile ) {}
    virtual ~PlayMusic() { cout << "~PlayMusic()" << endl; }
       
    void operator()()
    {
        cout << "PlayMusic " << m_song << endl;
    }
    virtual Action *clone() const
    {
        return (Action *)this;
    }
private:
    string m_song;
};

int main(int argc, char *argv[])
{
    Button *b = new Button( "Anoko no namaewa" );
    PlayMusic *song = new PlayMusic( "AnokoNonamaewa.mp3" );
    b->setAction( song );
    b->onClick();
   
    delete b;
   
  system("PAUSE"); 
  return 0;
}