单例类的实现(1)

最新推荐文章于 2024-07-04 23:00:52 发布

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最新推荐文章于 2024-07-04 23:00:52 发布

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文章标签： c/c++ 游戏

原文链接：http://www.cnblogs.com/mikewolf2009/articles/1607211.html

单例类的实现(1)

游戏引擎中经常用到单例(singleton)类，即应用程序只存在该类的一个实例，下面是它的实现方式：

1、c++ professional中的单例日志类：定义一个protected的static Logger sInstance;然后通过public静态函数

static Logger& instance();返回sInstance，从而实现对该类中函数的访问。同时，该类的构造函数是私有的，我们不能通过构造函数创建该类的实例。

Code
/**
* Logger.h
*
* Definition of a true singleton logger class.
*/
#include <iostream>
#include <fstream>
#include <vector>

class Logger
{
public:
  static const std::string kLogLevelDebug;
  static const std::string kLogLevelInfo;
  static const std::string kLogLevelError;

  // Returns a reference to the singleton Logger object
  static Logger& instance();

  // Logs a single message at the given log level
  void log(const std::string& inMessage,
       const std::string& inLogLevel);

  // Logs a vector of messages at the given log level
  void log(const std::vector<std::string>& inMessages,
       const std::string& inLogLevel);

protected:
  // Static variable for the one-and-only instance
  static Logger sInstance;

  // Constant for the file namename
  static const char* const kLogFileName;

  // Data member for the output stream
  std::ofstream mOutputStream;

private:
  Logger();
  ~Logger();

};

Code
/**
* Logger.cpp
*
* Implementation of a singleton logger class.
*/
#include <string>
#include "Logger.h"

using namespace std;

const string Logger::kLogLevelDebug = "DEBUG";
const string Logger::kLogLevelInfo = "INFO";
const string Logger::kLogLevelError = "ERROR";

const char* const Logger::kLogFileName = "log.out";

// The static instance will be constructed when the program starts and
// destructed when it ends.
Logger Logger::sInstance;

Logger& Logger::instance()
{
  return sInstance;
}

Logger::~Logger()
{
  mOutputStream.close();
}

Logger::Logger()
{
  mOutputStream.open(kLogFileName, ios_base::app);
  if (!mOutputStream.good()) {
    cerr << "Unable to initialize the Logger!" << endl;
  }
}

void Logger::log(const string& inMessage, const string& inLogLevel)
{
  mOutputStream << inLogLevel << ": " << inMessage << endl;
}

void Logger::log(const vector<string>& inMessages, const string& inLogLevel)
{
  for (size_t i = 0; i < inMessages.size(); i++) {
    log(inMessages[i], inLogLevel);
  }
}

int main(int argc, char** argv)
{
  Logger::instance().log("test message", Logger::kLogLevelDebug);

  vector<string> items;
  items.push_back("item1");
  items.push_back("item2");

  Logger::instance().log(items, Logger::kLogLevelError);
}

2、Game AI ...中的代码：

和前面的基本一样，但是在getinstance中来定义一个指向该类的静态变量，效果和上面一样，该函数第一次调用时候，会创建该静态变量。

Code
class VisitBankAndDepositGold : public State<Miner>
{
private:

  VisitBankAndDepositGold(){}

  //copy ctor and assignment should be private
  VisitBankAndDepositGold(const VisitBankAndDepositGold&);
  VisitBankAndDepositGold& operator=(const VisitBankAndDepositGold&);

public:

  static VisitBankAndDepositGold* Instance();

  virtual void Enter(Miner* miner);

  virtual void Execute(Miner* miner);

  virtual void Exit(Miner* miner);
};

//----------------------------------------methods for VisitBankAndDepositGold

VisitBankAndDepositGold* VisitBankAndDepositGold::Instance()
{
  static VisitBankAndDepositGold instance;

  return &instance;
}

void VisitBankAndDepositGold::Enter(Miner* pMiner)
{
  //on entry the miner makes sure he is located at the bank
  if (pMiner->Location() != bank)
  {
    cout << "\n" << GetNameOfEntity(pMiner->ID()) << ": " << "Goin' to the bank. Yes siree";

    pMiner->ChangeLocation(bank);
  }
}

void VisitBankAndDepositGold::Execute(Miner* pMiner)
{
  //deposit the gold
  pMiner->AddToWealth(pMiner->GoldCarried());

  pMiner->SetGoldCarried(0);

  cout << "\n" << GetNameOfEntity(pMiner->ID()) << ": "
       << "Depositing gold. Total savings now: "<< pMiner->Wealth();

  //wealthy enough to have a well earned rest?
  if (pMiner->Wealth() >= ComfortLevel)
  {
    cout << "\n" << GetNameOfEntity(pMiner->ID()) << ": "
         << "WooHoo! Rich enough for now. Back home to mah li'lle lady";

    pMiner->GetFSM()->ChangeState(GoHomeAndSleepTilRested::Instance());
  }

  //otherwise get more gold
  else
  {
    pMiner->GetFSM()->ChangeState(EnterMineAndDigForNugget::Instance());
  }

}

void VisitBankAndDepositGold::Exit(Miner* pMiner)
{
  cout << "\n" << GetNameOfEntity(pMiner->ID()) << ": " << "Leavin' the bank";
}