我要向大家介绍一下这部令我困惑的那部法典。

   //-------------------------------------------------------------------------------
   // 3.5 Example B: Callback to member function using a global variable
   // Task: The function  DoItB  does something that implies a callback to
   //       the member function  Display . Therefore the wrapper-function
   //        Wrapper_To_Call_Display is used.

   #include <iostream.h>   // due to:   cout

   void* pt2Object;        // global variable which points to an arbitrary object

   class TClassB
   {
   public:

      void Display(const char* text) { cout << text << endl; };
      static void Wrapper_To_Call_Display(char* text);

      /* more of TClassB */
   };


   // static wrapper-function to be able to callback the member function Display()
   void TClassB::Wrapper_To_Call_Display(char* string)
   {
       // explicitly cast global variable <pt2Object> to a pointer to TClassB
       // warning: <pt2Object> MUST point to an appropriate object!
       TClassB* mySelf = (TClassB*) pt2Object;

       // call member
       mySelf->Display(string);
   }


   // function does something that implies a callback
   // note: of course this function can also be a member function
   void DoItB(void (*pt2Function)(char* text))
   {
      /* do something */

      pt2Function("hi, i m calling back using a global ;-)");   // make callback
   }


   // execute example code
   void Callback_Using_Global()
   {
      // 1. instantiate object of TClassB
      TClassB objB;


      // 2. assign global variable which is used in the static wrapper function
      // important: never forget to do this!!
      pt2Object = (void*) &objB;


      // 3. call  DoItB  for <objB>
      DoItB(TClassB::Wrapper_To_Call_Display);
   }

问题1: 关于这项职能:

DoItB(TClassB::Wrapper_To_Call_Display)

为什么Wrapper_To_Call_Display不提出任何论点,尽管根据声明应当采用char*的论点?

<><> <><><>>>>>>><>>>>>>>

void DoItB(void (*pt2Function)(char* text))

我迄今所理解的是:<代码>。 DoItB 以职能要点为理由,但为何职能称为<代码>。 DoItB(TClassB):Wrapper_To_Call_Display)。 甚至可以说,它不是指人吗?

预兆

Source of code snippet: http://www.newty.de/fpt/callback.html