Thread: insert linked list - segment violation

what is wrong with this function? This function insert a new node in the linked list, but it'not works.

Code:

void insertFrontierAstar ( FrontierNodePtr *headPtr, TreeNodePtr ptr )
{
	FrontierNodePtr currentPtr, previousPtr;
	
	FrontierNodePtr newPtr;

	newPtr = malloc ( sizeof ( FrontierNode ) );

	if ( newPtr == NULL )                            
	{
		printf( "can't allocate memory for FrontierNodePtr\nexit program\n" );
		exit ( 3 );
	}

	else
	{
		newPtr->leaf = ptr;
		newPtr->next = NULL;

		previousPtr = NULL;
		currentPtr = *headPtr;

		while ( currentPtr != NULL && currentPtr->leaf->sum < newPtr->leaf->sum )
		{
			previousPtr = currentPtr;
			currentPtr = currentPtr->next;
		}

		if ( previousPtr == NULL )
		{
			newPtr->next = *headPtr;
			*headPtr = newPtr;
			return;
		}

		if ( currentPtr->leaf->sum > newPtr->leaf->sum )
		{
			previousPtr->next = newPtr;
			newPtr->next = currentPtr;
		}

		if ( currentPtr->leaf->sum == newPtr->leaf->sum )
		{
			while ( currentPtr->leaf->g >= newPtr->leaf->g )
			{
				previousPtr = currentPtr;
				currentPtr = currentPtr->next;
			}

			previousPtr->next = newPtr;
			newPtr->next = currentPtr;

		}





	}



}

thank you in advance

Code:

		if ( currentPtr->leaf->sum > newPtr->leaf->sum )
		{
			previousPtr->next = newPtr;
			newPtr->next = currentPtr;
		}

		if ( currentPtr->leaf->sum == newPtr->leaf->sum )
		{
			while ( currentPtr->leaf->g >= newPtr->leaf->g )
			{
				previousPtr = currentPtr;
				currentPtr = currentPtr->next;
			}

			previousPtr->next = newPtr;
			newPtr->next = currentPtr;

		}

This section can be entered with currentPtr == NULL - which will cause segmentation fault, of course.

--
Mats

thank You Mats, for quick response. I' will check it

Before dereferencing any pointers, be sure to check them for NULL!

well, i learn my lesson, thank you Mats (again) and Elysia, you are the best,
here is my function, completed and running.

Code:

void insertFrontierAstar ( FrontierNodePtr *headPtr, FrontierNodePtr *tailPtr, TreeNodePtr ptr )
{
	FrontierNodePtr currentPtr, previousPtr;  
	FrontierNodePtr newPtr;

	newPtr = malloc ( sizeof ( FrontierNode ) );

	if ( newPtr == NULL )                             
	{
		printf( "can't allocate memory for FrontierNodePtr\nexit program\n" );
		exit ( 3 );
	}

	else
	{
		newPtr->leaf = ptr;
		newPtr->next = NULL;

		if ( *headPtr == NULL )
		{
			newPtr->next = *headPtr;
			*headPtr = newPtr;
		}

		else
		{
			previousPtr = NULL;
			currentPtr = *headPtr;

			if ( currentPtr->leaf->sum > newPtr->leaf->sum )
			{
				newPtr->next = *headPtr;
				*headPtr = newPtr;
			}

			else if ( currentPtr->leaf->sum < newPtr->leaf->sum )
			{
				while ( currentPtr != NULL && currentPtr->leaf->sum < newPtr->leaf->sum )
				{
					previousPtr = currentPtr;
					currentPtr = currentPtr->next;
				}

				if ( currentPtr == NULL )
				{
					( *tailPtr )->next = newPtr;
					*tailPtr = newPtr;
				}

				else if ( currentPtr != NULL && currentPtr->leaf->sum > newPtr->leaf->sum )
				{
					previousPtr->next = newPtr;
					newPtr->next = currentPtr;
				}

				else if ( currentPtr != NULL && currentPtr->leaf->sum == newPtr->leaf->sum )
				{
					while ( currentPtr != NULL && currentPtr->leaf->sum == newPtr->leaf->sum
							&& currentPtr->leaf->g >= newPtr->leaf->g )
					{
						previousPtr = currentPtr;
						currentPtr = currentPtr->next;
					}

					if ( currentPtr == NULL )
					{
						( *tailPtr )->next = newPtr;
						*tailPtr = newPtr;
					}

					else
					{
						previousPtr->next = newPtr;
						newPtr->next = currentPtr;
					}
				}
			}

			else
			{
				while ( currentPtr != NULL && currentPtr->leaf->sum == newPtr->leaf->sum
							&& currentPtr->leaf->g >= newPtr->leaf->g )
				{
					previousPtr = currentPtr;
					currentPtr = currentPtr->next;
				}

				if ( currentPtr == NULL )
				{
					( *tailPtr )->next = newPtr;
					*tailPtr = newPtr;
				}

				else if ( previousPtr == NULL )
				{
					newPtr->next = *headPtr;
					*headPtr = newPtr;
				}

				else
				{
					previousPtr->next = newPtr;
					newPtr->next = currentPtr;
				}
			}
		}

	}



}