PRODUCT  :  C++                                    NUMBER  :  652
  VERSION  :  All
       OS  :  PC DOS
     DATE  :  October 22, 1993                         PAGE  :  1/1

    TITLE  :  Interrupt Handlers as Member Functions





  A static member function of a  class  can be used as an interrupt
  handler.  It is not possible to use a 'regular or  normal' member
  function as  an Interrupt Handler because such functions expect a
  hidden parameter when called ( i.e. the 'this' pointer )  and the
  Intel interrupt mechanism cannot push the 'this' pointer prior to
  calling  a  handler.   ( See  your  C++  documentation  for  more
  information about the 'this' parameter passed to member functions
  ).


  The following  provides an example where a static member function
  is used  as  an  interrupt  handler.    The class also contains a
  pointer to an instance of  the  class,  therefore  providing more
  flexibility to the handler.    The  only  requirement is that the
  static pointer must be  initialized  to  a  valid instance of the
  class:


  #include <dos.h>
  #include <stdio.h>
  #include <conio.h>


  _CLASSDEF( ISR )

  class ISR
  {
          int    intNumber;
          void interrupt (*oldHandler)(...);

      public:
          static PISR  curISR;

          ISR( int );
         ~ISR();
          static void interrupt __handler(...);
          virtual void handler();

          virtual void justBeep();
  };
  PISR  ISR::curISR = NULL;














  PRODUCT  :  C++                                    NUMBER  :  652
  VERSION  :  All
       OS  :  PC DOS
     DATE  :  October 22, 1993                         PAGE  :  2/1

    TITLE  :  Interrupt Handlers as Member Functions




  ISR::ISR( int iNum )
  {
      intNumber  = iNum;
      oldHandler = getvect( intNumber );
      setvect( intNumber, (void interrupt(*)(...))__handler );
  }


  ISR::~ISR()
  {
      setvect( intNumber, (void interrupt (*)(...))oldHandler );
      curISR = NULL;
  }


  void interrupt ISR::__handler(...)
  {
      if ( curISR )
          curISR->handler();
  }


  void ISR::handler()
  {
      justBeep();
  }


  void ISR::justBeep()
  {
      _AX = 0x0E07;
      geninterrupt( 0x10 );
  }


  int main( void )
  {
      int  key = 0;
      ISR  myPrintISR( 5 );

      ISR::curISR = &myPrintISR;

      printf("Hit ESC to terminate or PrintScreen to trigger\n" );













  PRODUCT  :  C++                                    NUMBER  :  652
  VERSION  :  All
       OS  :  PC DOS
     DATE  :  October 22, 1993                         PAGE  :  3/1

    TITLE  :  Interrupt Handlers as Member Functions




      printf("the Interrupt 5 and listen to my Beep !\n" );

      while( key != 27 )
      {
          if ( !(key = getch()) )
              key = getch();
          putch( key );
      }
      return( 0 );
  }

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  subject to the terms  of  the  No-Nonsense License Statement that
  you received with  the  Borland product to which this information
  pertains.