一個(gè)類有且僅有一個(gè)實(shí)例，并且提供一個(gè)訪問(wèn)它的全局訪問(wèn)點(diǎn)。
要點(diǎn)：
1、類只能有一個(gè)實(shí)例；
2、必須自行創(chuàng)建此實(shí)例；
3、必須自行向整個(gè)系統(tǒng)提供此實(shí)例。

實(shí)現(xiàn)一：?jiǎn)卫Ｊ浇Y(jié)構(gòu)代碼

singleton.h文件代碼如下:

#ifndef _SINGLETON_H_
#define _SINGLETON_H_

class Singleton
{
public:
  static Singleton* GetInstance();
protected:
  Singleton();
private:
  static Singleton *_instance;
};

#endif

singleton.cpp文件代碼如下:

#include "singleton.h"
#include <iostream>
using namespace std;

Singleton* Singleton::_instance = 0;

Singleton::Singleton()
{
  cout<<"create Singleton ..."<<endl;
}

Singleton* Singleton::GetInstance()
{
  if(0 == _instance)
  {
    _instance = new Singleton();
  }
  else
  {
    cout<<"already exist"<<endl;
  }

  return _instance;
}

main.cpp文件代碼如下:

#include "singleton.h"

int main()
{
  Singleton *t = Singleton::GetInstance();
  t->GetInstance();

  return 0;
}

實(shí)現(xiàn)二：打印機(jī)實(shí)例

singleton.h文件代碼如下:

#ifndef _SINGLETON_H_
#define _SINGLETON_H_

class Singleton
{
public:
  static Singleton* GetInstance();
  void printSomething(const char* str2Print);
protected:
  Singleton();
private:
  static Singleton *_instance;
  int count;
};

#endif

singleton.cpp文件代碼如下:

#include "singleton.h"
#include <iostream>

using namespace std;

Singleton* Singleton::_instance = 0;

Singleton::Singleton()
{
  cout<<"create Singleton ..."<<endl;
  count=0;
}

Singleton* Singleton::GetInstance()
{
  if(0 == _instance)
  {
    _instance = new Singleton();
  }
  else
  {
    cout<<"Instance already exist"<<endl;
  }

  return _instance;
}

void Singleton::printSomething(const char* str2Print)
{
  cout<<"printer is now working , the sequence : "<<++count<<endl;
  cout<<str2Print<<endl;
  cout<<"done\n"<<endl;
}

main.cpp文件代碼如下:

#include "singleton.h"

int main()
{
  Singleton *t1 = Singleton::GetInstance();
  t1->GetInstance();
  t1->printSomething("t1");

  Singleton *t2 = Singleton::GetInstance();
  t2->printSomething("t2");
  return 0;
}

Makefile文件:

CC=g++
CFLAGS = -g -O2 -Wall

all:
  make singleton

singleton:singleton.o\
  main.o  
  ${CC} -o singleton main.o singleton.o

clean:
  rm -rf singleton
  rm -f *.o

.cpp.o:
  $(CC) $(CFLAGS) -c -o $*.o $<

運(yùn)行效果如下圖所示：