Destruction aids memory management in object-oriented C
Matthew Curreri
Embedded Systems Programming
October 2003

Listings

Listing 1:   The CApp class and main

typedef struct _CApp 
{
  CWndNav *m_pWndNav;

} CApp;


void 
main(void) 
{
  unsigned int	wParam;
  CApp *	pApp;


  pApp = (CApp *) malloc(sizeof(CApp));
  pApp->m_pWndNav = (CWndNav *) malloc(sizeof(CWndNav));

  pApp->m_pWndNav->New = mWndNavNew;
  pApp->m_pWndNav->New(pApp->m_pWndNav);

  while (1)
  {
     int nChoice;

     printf("Press	1 = View 1\n");
     printf("		2 = View 2\n");
     printf("		3 = Exit\n");
     scanf("%d", &nChoice);

     switch (nChoice) 
     {
        case 1: 
            wParam = ID_OPTION1; 
            break;

        case 2: 
            wParam = ID_OPTION2; 
            break;

        default: 
            return;
     }

     pApp->m_pWndNav->SendMessage(pApp->m_pWndNav, 0, wParam, 0L);
  }
};  



Listing 2   The CWndNav class  

*/typedef struct _CWndNav 
{
  CWndView *m_pobjWndView; 

  void (*Construct) (struct _CWndNav * _this);
  void (*Destruct) (struct _CWndNav * _this, CWndView *pobjWndNav);
  void (*SendMessage) (struct _CWndNav * _this, unsigned int Msg, 
    unsigned int wParam, long lParam);
  void (*New) (struct _CWndNav * _this);

} CWndNav;


void 
mWndNavConstructor(CWndNav * _this) 
{
  _this->m_pobjWndView = (CWndView *) malloc(sizeof(CWndView));

  _this->m_pobjWndView->New = mWndViewNew; // Assign new functional pointer
  _this->m_pobjWndView->New(_this->m_pobjWndView);   
  _this->m_pobjWndView->Construct(_this->m_pobjWndView);  
};

void 
mWndNavDestructor(CWndNav * _this, CWndView *pobjWndNav) 
{
  pobjWndNav->Destruct(pobjWndNav);
  free(pobjWndNav);
}

void 
mWndNavWndProc(CWndNav * _this, unsigned int Msg, unsigned int wParam, long lParam) 
{
  switch (wParam) 
  {
     case ID_OPTION1:
       _this->New(_this);
       _this->Construct(_this);
       _this->m_pobjWndView->SendMessage(_this->m_pobjWndView, 0, wParam,
         (long)"View 1" );
       _this->Destruct(_this, _this->m_pobjWndView);
       break;

     case ID_OPTION2:
       _this->New(_this);
       _this->Construct(_this);
       _this->m_pobjWndView->SendMessage(_this->m_pobjWndView, 0, wParam,
         (long)"View 2" );
       _this->Destruct(_this, _this->m_pobjWndView);
       break;
  }
}

void 
mWndNavNew(CWndNav * _this) 
{
  _this->Construct    = mWndNavConstructor;
  _this->Destruct     = mWndNavDestructor;
  _this->SendMessage  = mWndNavWndProc;
}



Listing 3   The CButton and CWndView classes

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ID_OPTION1 0
#define ID_OPTION2 1


typedef struct _CButton 
{
  void (*Construct)(struct _CButton * _this);
  void (*Paint) (struct _CButton * _this, char * strCaption, int nLineNumber);
  void (*GotFocus) (struct _CButton * _this, char * strCaption, int nLineNumber);
  void (*New) (struct _CButton * _this);

} CButton;

void 
mButtonConstructor(CButton * _this) 
{
  // assignment of resources ‹
}

void 
mButtonPaint(CButton * _this, char * strCaption, int nLineNumber) 
{
  switch (nLineNumber) 
  {
     case 0: 
       printf(" _________ "); 
       break;

     case 1:
       printf("(         )"); 
       break;

     case 2: 
       printf("( %s )", strCaption); 
       break;

     case 3: 
       printf("(_________)"); 
       break;
  }
}

void 
mButtonGotFocus(CButton * _this, char * strCaption, int nLineNumber) 
{
  switch (nLineNumber) 
  {
     case 0: 
       printf("           "); 
       break;

     case 1:
       printf("(*********)"); 
       break;

     case 2: 
       printf("(*%s*)", strCaption); 
       break;

     case 3: 
       printf("(*********)"); 
       break;
  }
}

void 
mButtonNew(CButton * _this) 
{
  _this->Construct = mButtonConstructor;
  _this->Paint = mButtonPaint;
  _this->GotFocus = mButtonGotFocus;
  _this->New = mButtonNew;
}


typedef struct _CWndView 
{
  CButton  *m_pButton;

  void (*Construct) (struct _CWndView * _this);
  void (*Destruct) (struct _CWndView * _this);
  void (*SendMessage) (struct _CWndView * _this, unsigned int Msg, 
    unsigned int wParam, long lParam);
  void (*New) (struct _CWndView * _this);

} CWndView;

void 
mWndViewConstructor(CWndView * _this) 
{
  // assignment of resources ‹
}

void 
mWndViewDestructor(CWndView * _this) 
{
  free(_this->m_pButton);
}

void 
mWndViewWndProc(CWndView * _this, unsigned int Msg, unsigned int wParam, 
  long lParam) 
{
  switch (wParam) 
  {
     case ID_OPTION1:
       _this->m_pButton->GotFocus(_this->m_pButton, "Option1", 0);
       printf(" _____________________________\n");
       _this->m_pButton->GotFocus(_this->m_pButton, "Option1", 1);
       printf("(                             )\n");
       _this->m_pButton->GotFocus(_this->m_pButton, "Option1", 2);
       printf("(                             )\n");
       _this->m_pButton->GotFocus(_this->m_pButton, "Option1", 3);
       printf("(      %s                 )\n", (char *) lParam);

       _this->m_pButton->Paint(_this->m_pButton, "Option2", 0);
       printf("(                             )\n");
       _this->m_pButton->Paint(_this->m_pButton, "Option2", 1);
       printf("(                             )\n");
       _this->m_pButton->Paint(_this->m_pButton, "Option2", 2);
       printf("(                             )\n");
       _this->m_pButton->Paint(_this->m_pButton, "Option2", 3);
       printf("(_____________________________)\n\n\n");
       break;

     case ID_OPTION2:
       _this->m_pButton->Paint(_this->m_pButton, "Option1", 0);
       printf(" _____________________________\n");
       _this->m_pButton->Paint(_this->m_pButton, "Option1", 1);
       printf("(                             )\n");
       _this->m_pButton->Paint(_this->m_pButton, "Option1", 2);
       printf("(                             )\n");
       _this->m_pButton->Paint(_this->m_pButton, "Option1", 3);
       printf("(      %s                 )\n", (char *)lParam);

       _this->m_pButton->GotFocus(_this->m_pButton, "Option2", 0);
       printf("(                             )\n");
       _this->m_pButton->GotFocus(_this->m_pButton, "Option2", 1);
       printf("(                             )\n");
       _this->m_pButton->GotFocus(_this->m_pButton, "Option2", 2);
       printf("(                             )\n");
       _this->m_pButton->GotFocus(_this->m_pButton, "Option2", 3);
       printf("(_____________________________)\n\n\n");
       break;
  }
}

void 
mWndViewNew(CWndView * _this) 
{
  _this->m_pButton = (CButton *) malloc(sizeof(CButton));

  _this->m_pButton->New = mButtonNew;  // Assign new functional pointer
  _this->m_pButton->New(_this->m_pButton);   

  _this->Construct = mWndViewConstructor;
  _this->Destruct = mWndViewDestructor;
  _this->SendMessage = mWndViewWndProc;
}