search a Binary search tree

Question

I am trying to find a name within a key. I think it is retrieving it fine. however, its coming up as not found. maybe my code is wrong somewhere?

if (database.retrieve(name, aData))  // both contain the match

in main()

static void retrieveItem(char *name, data& aData)
{
cout << ">>> retrieve " << name << endl << endl;
if (database.retrieve(name, aData))            // name and aData both contain the match
    cout << aData << endl;
else
    cout << "not found\n";
cout << endl;
     }

     static void removeItem(char *name)
    {
cout << ">>> remove " << name << endl << endl;
if (database.remove(name))
    cout << name << " removed\n";
else
    cout << name << " not found\n";
cout << endl;
    }

   int main()
   {
   #ifdef _WIN32
// request memory leak report in Output Window after main returns
_CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF );
   #endif

data    aData;


     << "Database Of Great Computer Scientists\n\n";

database.insert(data("Ralston, Anthony"));
database.insert(data("Liang, Li"));
database.insert(data("Jones, Doug"));
database.insert(data("Goble, Colin"));
database.insert(data("Knuth, Donald"));
database.insert(data("Kay, Alan"));
database.insert(data("Von Neumann, John"));
database.insert(data("Trigoboff, Michael"));
database.insert(data("Turing, Alan"));
displayDatabase(true);
retrieveItem("Trigoboff, Michael", aData);
retrieveItem("Kaye, Danny", aData);

removeItem("Ralston, Anthony");
displayDatabase(true);

retrieve function...

bool BST::retrieve(const char *key, data &aData, int parent) const
 {

for(int index=0; index < maxsize+1; index++)
{

    if (!items[index].empty) 
    {


        if ( items[index].instanceData == key )
        {
            aData.setName(key);
            return true;                   // doesn't return right away
        }


    }

}


 }

and defined in data.cpp

bool operator== (const data& d1, const data& d2)
{

return strcmp(d1.getName(), d2.getName()) == 0;

}

so this bit of code inside main() is where it says not found when i think it should be working correctly. both name and aData contain the right name that was found..

static void retrieveItem(char *name, data& aData)
{
cout << ">>> retrieve " << name << endl << endl;
if (database.retrieve(name, aData))            // name and aData both contain the match
    cout << aData << endl;
else
    cout << "not found\n";
cout << endl;
     }

Answer 1

You should be using the BST to navigate through the tree - not looping over each item in your array, like others have said. Try something like:

bool retrieve(key, aData)
  retrieve(key, aData, parent)
  if (key == aData)
    return true
  else
    return false

bool retrieve(key, aData, parent)
  if (key == items[parent].name)
    aData.setName(key)
  else if (key < items[parent].name)
    retrieve(key, aData, 2*parent+1)
  else
    retrieve(key, aData, 2*parent+2)

That should work well! :)

Answer 2

I'm no C++ expert, but is your == operator actually being evaluated? It's meant to take two const data references, but you appear to be comparing whatever the type of items[index].instanceData is and a char*.

I suggest you put some logging into the operator and see if it's actually being called - I suspect it's not.

One option to take the == operator out of the equation temporarily would be to make the comparison explicit:

 if (strcmp(items[index].instanceData.getName(), key) == 0)
 {
     ...
 }

On another point, I can't see how this is actually doing a binary search at all. It looks to me like it's just a plain list - you're doing a linear search within retrieve instead of comparing the key and going left or right down the tree (or returning "found") depending on the result.

Answer 3

I can't tell for sure without seeing the code for BST, but this looks wrong:

for(int index=0; index < maxsize+1; index++)

With the traditional conventions, it should be:

for(int index=0; index < maxsize; index++)

Beside that, it also seems your function either returns true or some undefined boolean. You should probably have a return false; at the end of BST::retrieve.