Delete Function in Doubly Linked List
Hello, I am having trouble with my doubly linked list program. My insert function seems to work fine, but where I'm having trouble is the delete function.. Problem is when i try to delete from the beginning or end of the list, the program crashes in the printbackwards. Depending on the order I try to delete, I can delete the middle characters first and then the program crashes after I try to delete the first and last characters. It seems to be a problem with my prevPtr, but I cannot see where I'm going wrong. Here are my insert/delete/printbackwards functions
Code:
void insert ( ListNodePtr *sPtr, char value)
{
ListNodePtr newPtr; /* pointer to a new node */
ListNodePtr previousPtr; /* pointer to previous node in list */
ListNodePtr currentPtr; /* pointer to current node on list */
newPtr = malloc( sizeof( ListNode )); /* create node */
if ( newPtr != NULL ) { /* is space available */
newPtr->data = value; /*place value in node */
newPtr->nextPtr = NULL; /*node does not link to another node */
newPtr->prevPtr = NULL;
previousPtr = NULL;
currentPtr = *sPtr;
/* loop to find the correct location in the list */
while (currentPtr != NULL && value > currentPtr->data ) {
previousPtr = currentPtr; /* walk to...*/
currentPtr = currentPtr->nextPtr; /* .....next node */
} /* end while */
/* insert new node at begining of list */
if ( previousPtr == NULL ) {
newPtr->nextPtr = *sPtr;
if(*sPtr != NULL)
(*sPtr)->prevPtr = newPtr;
*sPtr = newPtr;
} /* end if */
else { /* insert new node between previousPtr and currentPtr */
newPtr->prevPtr = previousPtr;
previousPtr->nextPtr = newPtr;
newPtr->nextPtr = currentPtr;
if (currentPtr != NULL)
currentPtr->prevPtr = newPtr;
} /* end else */
} /* end if */
else {
printf( "%c not inserted. No memory available.\n", value );
} /* end else */
} /* end function insert */
char delete ( ListNodePtr *sPtr, char value )
{
ListNodePtr previousPtr; /* pointer to previous node on list */
ListNodePtr currentPtr; /* pointer to current node on list */
ListNodePtr tempPtr; /* temperary node pointer */
/* delete first node */
if (value == ( *sPtr )->data) {
tempPtr = *sPtr; /* hold onto node being removed */
*sPtr = ( *sPtr )->nextPtr; /* de-thread the node */
free( tempPtr ); /* free the de-threaded node */
return value;
} /* end if */
else {
previousPtr = *sPtr;
currentPtr = ( *sPtr )->nextPtr;
/* loop to find correct location on list */
while ( currentPtr != NULL && currentPtr->data != value ) {
previousPtr = currentPtr; /* walk to ....*/
currentPtr = currentPtr->nextPtr; /*....next node*/
} /* end while */
/* delete node at currentPtr */
if ( currentPtr != NULL ) {
tempPtr = currentPtr;
previousPtr->nextPtr = currentPtr->nextPtr;
currentPtr = previousPtr;
currentPtr->nextPtr->prevPtr = previousPtr;
free ( tempPtr );
return value;
} /* end if */
} /* end else */
return '\0';
} /* end function delete */
void printBackwards ( ListNodePtr currentPtr )
{
ListNodePtr temp = NULL;
while ( currentPtr != NULL ) {
temp = currentPtr;
currentPtr = currentPtr->nextPtr;
}
printf( "\nThe list in reverse is:\n" );
printf( "NULL" );
currentPtr = temp;
while ( currentPtr != NULL) {
printf( " <-- %c", currentPtr->data );
currentPtr = currentPtr->prevPtr;
}
printf("\n\n");
} /* end function printBackwards */
