Printing to File using BST.

[omGeeK]

So, I just started Binary Search Trees in class this week, and this is part of a sample program to print student names to the stdout. For my program that I have to do I must print to a file, now I have tried a lot of times and the problem is that when I create a file in my "processStu" function is there a way to keep the file open and not reopen or close everytime the function is called. Or should make a loop somehow? I'm stuck here, I'm thinking of writing a new function using completely different logic just want to know if i can do it this way somehow and save a lot of time.

-- In the sample all it calls is the printList function once to print the entire tree in inorder --

Regards
omGeeK

/*	==================== printList ======================  
	Prints the phone book.
	    Pre  list has been created (may be null)
	    Post printed
*/
void printList  (BST_TREE* list)
{
//	Statements 
	printf("\n*Name List*\n");
	BST_Traverse (list, processStu);
	printf("*End of List*\n");
	return;
}	// printList 

/*	=================== BST_Traverse =================== 
	Process tree using inorder traversal. 
	   Pre   Tree has been created (may be null) 
	         process ÒvisitsÓ nodes during traversal 
	   Post  Nodes processed in LNR (inorder) sequence 
*/
void BST_Traverse (BST_TREE* tree, 
                   void (*process) (void* dataPtr)) 
{
//	Statements 
	_traverse (tree->root, process);
	return;
}  // end BST_Traverse 

/*	=================== _traverse =================== 
	Inorder tree traversal. To process a node, we use 
	the function passed when traversal was called.
	   Pre   Tree has been created (may be null) 
	   Post  All nodes processed 
*/
void _traverse (NODE* root, 
                void (*process) (void* dataPtr)) 
{
//	Statements 
if  (root)
    {
     _traverse (root->left, process);
     process   (root->dataPtr);
     _traverse (root->right, process);
    } // if 
return;
}  // _traverse

/*	=================== processStu =====================  
	Print one student's data.
	    Pre  stu is a pointer to a student
	    Post data printed and line advanced
*/
void processStu (void* stuPtr)
{
//	Local Definitions 
	STUDENT aStu;
	
//	Statements 
	aStu = *(STUDENT*)stuPtr;
	printf("%-25s %s\n", 
	       aStu.name,aStu.phone);
	return;
}	// processStu

[rags_to_riches]

What "processStu" function? I don't see one. The answer is to open the FILE before you traverse the tree and pass the FILE pointer along to the functions.

[omGeeK]

Sorry forgot to put it in there, its there now.

[Salem]

A way to help callback functions like this (you pass a pointer to a function to some generic routine, and it calls your function), is to arrange it so that you can also pass a "void *userData" pointer along for the ride.

This user data pointer can be anything (it's void*). Use it to maintain any kind of context that your processing function needs from one call to the next.

In this example, the user data is just a FILE*

/*  ==================== printList ======================
    Prints the phone book.
        Pre  list has been created (may be null)
        Post printed
*/
void printList  (BST_TREE* list)
{
//  Statements
    printf("\n*Name List*\n");
    BST_Traverse (list, processStu,stdout);
    {
      FILE *fp = fopen("file.txt","w");
      BST_Traverse (list, processStu,fp);
      fclose(fp);
    }
    printf("*End of List*\n");
    return;
}   // printList

/*  =================== BST_Traverse ===================
    Process tree using inorder traversal.
       Pre   Tree has been created (may be null)
             process ÒvisitsÓ nodes during traversal
       Post  Nodes processed in LNR (inorder) sequence
*/
void BST_Traverse (BST_TREE* tree,
                   void (*process) (void* dataPtr, void *userData), void *userData)
{
//  Statements
    _traverse (tree->root, process, userData);
    return;
}  // end BST_Traverse

/*  =================== _traverse ===================
    Inorder tree traversal. To process a node, we use
    the function passed when traversal was called.
       Pre   Tree has been created (may be null)
       Post  All nodes processed
*/
void _traverse (NODE* root,
                void (*process) (void* dataPtr, void *userData), void *userData)
{
//  Statements
if  (root)
    {
     _traverse (root->left, process, userData);
     process   (root->dataPtr, userData);
     _traverse (root->right, process, userData);
    } // if
return;
}  // _traverse

/*  =================== processStu =====================
    Print one student's data.
        Pre  stu is a pointer to a student
        Post data printed and line advanced
*/
void processStu (void* stuPtr, void *userData)
{
//  Local Definitions
    STUDENT aStu;

//  Statements
    aStu = *(STUDENT*)stuPtr;
    fprintf(userData, "%-25s %s\n",
           aStu.name,aStu.phone);
    return;
}   // processStu

[omGeeK]

Thanks helped alot man