Question

我正在尝试实现模板单例模式，但是我收到了以下错误。我该如何克服这个错误？

下面是singleton_template.h

#include <iostream>
#include <string>
/*
* Burada yapılan herşey ".h" dosyası içerinde olmalı
*/
template<typename T>
class Singleton
{
private:
   static T* _instance;
   Singleton(const Singleton&);
   Singleton & operator=(const Singleton& rhs);

protected:
   Singleton();

public:
   static T* getInstance()
   {
     if(!_instance)
     _instance = new T;
     return _instance;
   }

   void destroyInstance()
   {
       delete _instance;
       _instance = NULL;
   }
};

template<typename T>
T* Singleton<T>::_instance= NULL;

这是singleton_template.cpp

#include <iostream>
#include <string>
#include "singleton_template.h"

class GKM : public Singleton<GKM>
{
public:

  GKM()
  {
    std::cout << "Single GKM created"<<std::endl;
  }
  virtual void initialize(){return;}

};

class Turnstile: public GKM 
{
public:
  Turnstile(){std::cout << "Single turnstile created add: "<< this<<std::endl;}
  virtual void initialize(){std::cout <<"Turnstile"<< std::endl;}

};

int main()
{
  GKM* trn= Turnstile::getInstance();
  trn->initialize();
  return 0;
}

以下是编译失败后的结果：

/tmp/ccfD0Xgx.o：在函数GKM::GKM()中： singleton_template.cpp :(。text._ZN3GKMC2Ev [_ZN3GKMC5Ev] + 0xd）：undefined 引用Singleton<GKM>::Singleton() collect2：error：ld 返回1退出状态

Answer 1

您没有实现Singleton类的默认构造函数，因为您继承了Singleton类，所以需要它。你可以改变

Singleton();

行到

Singleton() {}

然而，当我阅读你的代码时，它无论如何都不会按预期工作，因为

GKM* trn= Turnstile::getInstance();

实际上只创建了GKM个对象，而不是Turnstile，因为Singleton上有GKM，而Turnstile上没有import os import glob import re my_dir = 'whatever dir' special_filelist = dict() filelist = [] os.chdir( my_dir ) for files in glob.glob( "*.csv" ) : filelist.append(files) fileListName = re.match(r'(.*)[0-9]', files).group(1) if (fileListName not in special_filelist): special_filelist[fileListName] = [] special_filelist[fileListName].append(files) print special_filelist。（或者这是打算？）

Singleton-Inheritance C ++实现

1 个答案: