C/C++ Users Group Library 1996 July/C-C++ Users Group Library July 1996.iso/listings/v_08_03/8n03110a

Text File | 1990-03-18 | 5KB | 259 lines

*****Listing 3*****

// LIST.CPP - implementation of non-specific double linked lists

#include <stream.hpp>
#include <stddef.h>
#include <string.h>
#include "list.hpp"

LIST::LIST()      // constructor
   {
   head = curr = tail = NULL;
   }

LIST::~LIST()     // destructor
   {
   struct listelem *work;

   while(head != NULL)
      {
      delete_data(head);
      work = head->next;
      delete head;
      head = work;
      }
   }

void *LIST::get_head(unsigned int &sz)
   {
   curr = head;
   return get_curr(sz);
   }

void *LIST::get_curr(unsigned int &sz)
   {
   if(curr == NULL)
      {
      sz = 0;
      return NULL;
      }
   sz = curr->size;
   return curr->data;
   }

void *LIST::get_tail(unsigned int &sz)
   {
   curr = tail;
   return get_curr(sz);
   }

void *LIST::get_prev(unsigned int &sz)
   {
   if(curr->prev != NULL)
      {
      curr = curr->prev;
      return get_curr(sz);
      }
   else
      {
      sz = 0;
      return NULL;
      }
   }

void *LIST::get_next(unsigned int &sz)
   {
   if(curr->next != NULL)
      {
      curr = curr->next;
      return get_curr(sz);
      }
   else
      {
      sz = 0;
      return NULL;
      }
   }

void LIST::add_before(void *vptr, unsigned int sz)
   {
   struct listelem *lptr;

   lptr = new struct listelem;
   if(lptr == NULL)
      exit(99);         // ugly - should be fixed later

   lptr->size = sz;
   create_data(lptr);
   copy_data(lptr,vptr);

   // rearrange pointers

   if(curr != NULL)
      {
      lptr->prev = curr->prev;
      lptr->next = curr;

      if(lptr->prev != NULL)
         lptr->prev->next = lptr;
      else
         head = lptr;

      curr->prev = lptr;
      }
   else     // curr == NULL - must be first element in list
      {
      lptr->prev = lptr->next = NULL;
      head = curr = tail = lptr;
      }
   }

void LIST::add_after(void *vptr, unsigned int sz)
   {
   struct listelem *lptr;

   lptr = new struct listelem;
   if(lptr == NULL)
      exit(99);         // ugly - should be fixed later

   lptr->size = sz;
   create_data(lptr);
   copy_data(lptr,vptr);

   // rearrange pointers

   if(curr != NULL)
      {
      lptr->prev = curr;
      lptr->next = curr->next;

      curr->next = lptr;

      if(lptr->next != NULL)
         lptr->next->prev = lptr;
      else
         tail = lptr;
      }
   else     // curr == NULL - must be first element in list
      {
      lptr->prev = lptr->next = NULL;
      head = curr = tail = lptr;
      }
   }

void LIST::add_head(void *vptr, unsigned int sz)
   {
   struct listelem *lptr;

   lptr = new struct listelem;
   if(lptr == NULL)
      exit(99);         // ugly - should be fixed later

   lptr->size = sz;
   create_data(lptr);
   copy_data(lptr,vptr);

   if(head != NULL)
      {
      lptr->prev = NULL;
      lptr->next = head;
      head->prev = lptr;
      head = lptr;
      }
   else
      {
      lptr->prev = lptr->next = NULL;
      head = curr = tail = lptr;
      }
   }

void LIST::add_tail(void *vptr, unsigned int sz)
   {
   struct listelem *lptr;

   lptr = new struct listelem;
   if(lptr == NULL)
      exit(99);         // ugly - should be fixed later

   lptr->size = sz;
   create_data(lptr);
   copy_data(lptr,vptr);

   if(tail != NULL)
      {
      lptr->next = NULL;
      lptr->prev = tail;
      tail->next = lptr;
      tail = lptr;
      }
   else
      {
      lptr->prev = lptr->next = NULL;
      head = curr = tail = lptr;
      }
   }

void LIST::delete_curr()
   {
   struct listelem *lptr;

   if(curr == NULL)
      return;

   lptr = curr;

   if(curr->prev != NULL)
      curr->prev->next = curr->next;
   else
      head = curr->next;

   if(curr->next != NULL)
      curr->next->prev = curr->prev;
   else
      tail = curr->prev;

   if(curr->prev != NULL)
      curr = curr->prev;
   else if(curr->next != NULL)
      curr = curr->next;
   else if(head == NULL && tail == NULL)
      curr = NULL;      // list is now empty
   else
      {
      cerr << "LIST::delete_curr() : deletion sequence error\n";
      exit(99);
      }

   delete_data(lptr);
   delete lptr;
   }

// The following three functions should be replaced in all derived classes.
// create_data() should allocate and initialize space for a new instance of
// the class being stored in the list (implying that you should derive a new
// class for each type of object).  delete_data() should handle the destruction
// of class instances stored in a list.  copy_data() must take care of copying
// a complete class instance from one place to another - it must properly
// handle the situation where a class being stored in a list has
// dynamically-allocated storage.  As written these functions should properly
// handle all simple types (that is, types which have no dynamic storage).

void LIST::create_data(struct listelem *lptr)
   {
   lptr->data = new char[lptr->size];
   if(lptr->data == NULL)
      exit(99);
   }

void LIST::delete_data(struct listelem *lptr)
   {
   if(lptr->data != NULL)
      delete lptr->data;
   }

void LIST::copy_data(struct listelem *lptr, void *from)
   {
   memcpy(lptr->data,from,lptr->size);
   }