Single instance issue

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  • Sarath
    #1

    Single instance issue

    I've to write a single instance class. there are different methods to
    control the single instance of a program. I've tried the following
    method

    class CSingleton
    {
    public:
    CSingleton& GetInstance(){ static CSingleton s; return s; }

    private:
    CSingleton(){}
    ~CSingleton(){}
    }


    The above code failed to compile in Visual C++ 6.0 but compiled in
    Visual C++ 7.1 and Visual C++ Express 2008. CRT (in microsoft concept)
    calling the destructor of the class. So that Visual C++ 6.0
    compilation error (Failed to access destructor) is correct according
    to the concept.

    I also tried in Dev C++. It was successful but didn't call the dtor of
    the class. Which implementation is correct according to the standard.

    Sorry if off-topic to the forum
    Tags: None
    • Ian Collins
      #2
      Re: Single instance issue

      Sarath wrote:
      I've to write a single instance class. there are different methods to
      control the single instance of a program. I've tried the following
      method
      >
      class CSingleton
      {
      public:
      CSingleton& GetInstance(){ static CSingleton s; return s; }
      >
      How can you call this method and how would you change its definition if
      you did want to call it?
      private:
      CSingleton(){}
      ~CSingleton(){}
      }
      >
      It wouldn't compile with any compiler without the missing semicolon.
      The above code failed to compile in Visual C++ 6.0
      Never trust that compiler, it's old and not very standards compliant.

      --
      Ian Collins.

        Comment

        • Sarath
          #3
          Re: Single instance issue

          On Dec 21, 4:49 pm, Ian Collins <ian-n...@hotmail.co mwrote:
          Sarath wrote:
          I've to write a single instance class. there are different methods to
          control the single instance of a program. I've tried the following
          method
          >
          class CSingleton
          {
          public:
              CSingleton& GetInstance(){ static CSingleton s; return s; }
          >
          How can you call this method and how would you change its definition if
          you did want to call it?
          >
          private:
              CSingleton(){}
              ~CSingleton(){}
          }
          >
          It wouldn't compile with any compiler without the missing semicolon.
          >
          The above code failed to compile in Visual C++ 6.0
          >
          Never trust that compiler, it's old and not very standards compliant.
          >
          --
          Ian Collins.
          Dear All,
          I'm extremely sorry to paste wrong code. Please refer this one.

          class CSingle
          {
          public:
          static CSingle& GetInstance(){ static CSingle s; return s; }

          private:
          CSingle() { cout<<"ctor"; }
          ~CSingle() { cout<<"dtor"; }
          };

          Sorry for the incovenience.Pl ease refer this code for my question

          Regards,
          Sarath

            Comment

            • Salt_Peter
              #4
              Re: Single instance issue

              On Dec 21, 3:11 am, Sarath <CSar...@gmail. comwrote:
              On Dec 21, 4:49 pm, Ian Collins <ian-n...@hotmail.co mwrote:
              >
              >
              >
              Sarath wrote:
              I've to write a single instance class. there are different methods to
              control the single instance of a program. I've tried the following
              method
              >
              class CSingleton
              {
              public:
              CSingleton& GetInstance(){ static CSingleton s; return s; }
              >
              How can you call this method and how would you change its definition if
              you did want to call it?
              >
              private:
              CSingleton(){}
              ~CSingleton(){}
              }
              >
              It wouldn't compile with any compiler without the missing semicolon.
              >
              The above code failed to compile in Visual C++ 6.0
              >
              Never trust that compiler, it's old and not very standards compliant.
              >
              --
              Ian Collins.
              >
              Dear All,
              I'm extremely sorry to paste wrong code. Please refer this one.
              >
              class CSingle
              {
              public:
              static CSingle& GetInstance(){ static CSingle s; return s; }
              >
              private:
              CSingle() { cout<<"ctor"; }
              ~CSingle() { cout<<"dtor"; }
              >
              };
              >
              Sorry for the incovenience.Pl ease refer this code for my question
              >
              Regards,
              Sarath
              declare your destructor public. No reason to hide it.
              So what about the compiler generated copy constructor?

              int main()
              {
              CSingle instance;
              CSingle copy(instance);
              }

              and assignment? etc...



                Comment

                • Sarath
                  #5
                  Re: Single instance issue

                  On Dec 21, 5:41 pm, Salt_Peter <pj_h...@yahoo. comwrote:
                  On Dec 21, 3:11 am, Sarath <CSar...@gmail. comwrote:
                  >
                  >
                  >
                  On Dec 21, 4:49 pm, Ian Collins <ian-n...@hotmail.co mwrote:
                  >
                  Sarath wrote:
                  I've to write a single instance class. there are different methods to
                  control the single instance of a program. I've tried the following
                  method
                  >
                  class CSingleton
                  {
                  public:
                  CSingleton& GetInstance(){ static CSingleton s; return s; }
                  >
                  How can you call this method and how would you change its definition if
                  you did want to call it?
                  >
                  private:
                  CSingleton(){}
                  ~CSingleton(){}
                  }
                  >
                  It wouldn't compile with any compiler without the missing semicolon.
                  >
                  The above code failed to compile in Visual C++ 6.0
                  >
                  Never trust that compiler, it's old and not very standards compliant.
                  >
                  --
                  Ian Collins.
                  >
                  Dear All,
                  I'm extremely sorry to paste wrong code. Please refer this one.
                  >
                  class CSingle
                  {
                  public:
                  static CSingle& GetInstance(){ static CSingle s; return s; }
                  >
                  private:
                  CSingle() { cout<<"ctor"; }
                  ~CSingle() { cout<<"dtor"; }
                  >
                  };
                  >
                  Sorry for the incovenience.Pl ease refer this code for my question
                  >
                  Regards,
                  Sarath
                  >
                  declare your destructor public. No reason to hide it.
                  So what about the compiler generated copy constructor?
                  >
                  int main()
                  {
                  CSingle instance;
                  CSingle copy(instance);
                  >
                  }
                  >
                  and assignment? etc...
                  It will work if I make the dtor public. But I just want to know about
                  the destruction of static objects in the above scenario. As All
                  compilers behaves in different manner.

                  Regards,
                  Sarath

                    Comment

                    • James Kanze
                      #6
                      Re: Single instance issue

                      On Dec 21, 9:41 am, Salt_Peter <pj_h...@yahoo. comwrote:
                      On Dec 21, 3:11 am, Sarath <CSar...@gmail. comwrote:
                      I'm extremely sorry to paste wrong code. Please refer this one.
                      class CSingle
                      {
                      public:
                      static CSingle& GetInstance(){ static CSingle s; return s; }
                      private:
                      CSingle() { cout<<"ctor"; }
                      ~CSingle() { cout<<"dtor"; }
                      };
                      Sorry for the incovenience.Pl ease refer this code for my question
                      declare your destructor public. No reason to hide it.
                      There's also no reason to make it public, since the code should
                      work if the destructor is private as well. (A long time ago,
                      this was a frequent error, since the pre-standard specification
                      wasn't too clear as to where access of the destructor should be
                      checked. But any modern compiler should get it right.)
                      So what about the compiler generated copy constructor?
                      Good point.
                      int main()
                      {
                      CSingle instance;
                      CSingle copy(instance);
                      }
                      and assignment? etc...
                      Assignment would require two instances, or... Making it private
                      certainly doesn't hurt, however, and IMHO makes the intent
                      clearer.

                      --
                      James Kanze (GABI Software) email:james.kan ze@gmail.com
                      Conseils en informatique orientée objet/
                      Beratung in objektorientier ter Datenverarbeitu ng
                      9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

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