Thread: working with void pointers

I have the following functions :

Code:

typedef struct
{
char authors[5][40]; // first and last names of the author
char title[150]; // title of the publication
unsigned int year; // year of the publication
char isbn[15]; // publication code
} PubEntryT;


NodeST *findS(ListST *L, void *pKey, void * (*itemKey)(void *pItem), int(*keyCmp)(void *pKey1, void *pKey2))
// returns a pointer to the cell having a key equal to the one pointed to by pKey – if such a node exists
// on the list – or NULL if it cannot find such a node.
{
  NodeST *p;

  if (L != NULL)
   {
   if (L->first != NULL)
    {
      p = L->first;
     while ( p != NULL)
      {

        if ( keyCmp ( itemKey (p->Item),pKey) == 0)
              break;
         p=p->next;
      }
    }
    else {
           //errorSmessage(2);
           return NULL;
         }
  }
  return p;
}


void *itemKeyIsbn(void *pItem)
{ // for returning the isbn field of a book record
return ((PubEntryT *) pItem)->isbn;
}

int keyCmpStr(void *pKey1, void *pKey2)
{ // comparison of two ASCIIZ string keys; good for author or isbn comparison
return strcmp((char *)pKey1, (char *)pKey2);
}

I have to call this functions to find the node with a given key (a certain isbn, for example) and I use this call:

p = findS(L, pItem->Item,itemKeyIsbn(pItem),keyCmpStr(pItem->Item, pItem->Item)));
I'm not sure that my call is correct. In fact, I get segmentation fault in findS at the line

Code:

 
( keyCmp ( itemKey (p->Item),pKey) == 0)

Your findS function can return garbage if L is NULL, since it will return an uninitialized p. You do need to make sure that the pItem in your main function exists, because if you try to call pItem->Item when pItem is NULL (or uninitialized), then your program will die.

I didn't even look at the bit that wasn't in tags. That call should actually be

Code:

p = findS(L, pItem->Item, itemKeyIsbn, keyCmpStr);

You don't try to call a function when you want to pass a function name.

Originally Posted by HowardL

Oh I don't know , isn't findS() expecting pointer values to be returned by the functions in it's arguments:

Well, yes. But this function is not expecting an int* or a void * to be passed in, it's expecting a function so that the functions can be called by the function itself.