C++: Updating binary search tree using a recursive search function? - c++

Question

I'm in the middle of making a binary search tree that stores Items of type MechPart, which stores an int quantity and a string code. The MechParts are generated by reading from a text file and storing their data. A separate text file called MonthlyUpdate.txt is used to read a list of MechParts in the tree and then update their quantities. For example:
MechPart A0001's quantity = 12
MonthlyUpdate.txt says A0001's quantity = 6
Run an update function that finds A0001 in the tree
Replace it with the updated quantity value of 6 (12 - 6).
Here's the two functions that perform this task:
void DBInterface::updateFromFile(string f_Name)
{
ifstream file (f_Name.c_str());
string line;
MechPart tmp_mp;
if (file.is_open())
{
std::getline(file, line);
while (std::getline (file, line))
{
std::istringstream iss (line);
int q=0;
int pos=0;
pos = line.find('\t',0); //find position of blank space
string tmp_str = line.substr(0,pos); //create a substring
string tmp_str1 = line.substr((pos+1), string::npos);
stringstream ss (tmp_str1);
ss >> q;
tmp_mp.set_code(tmp_str); //set code
tmp_mp.set_quantity(q);
MechPart currentQuantity;
currentQuantity = tree.quantitySearch(tree.getRoot(), tmp_mp);
tmp_mp.set_quantity((currentQuantity.get_quantity()) + q);
tree.update(tree.getRoot(), tmp_mp);
cout << "Current node data: " << tmp_mp.get_code() << " | " << tmp_mp.get_quantity() << endl;
}
}
and BSTree.template:
template <typename Item>
Item BSTree<Item>::quantitySearch(BTNode<Item>* q_ptr, Item obj)
{
if (q_ptr == NULL)
{
//POINTER IS NULL
}
else if (q_ptr->data() == obj)
{
return q_ptr->data();
}
else if (obj > q_ptr->data())
{ //WORK ON RIGHT SIDE
quantitySearch(q_ptr->get_right(), obj);
}
else
{
//work on left side
quantitySearch(q_ptr->get_left(), obj);
}
}
The search goes through the tree and locates a MechPart with the same part name code as the parameter and then returns that MechPart.
I've been running the code through GDB debugger. I have it displaying currentQuantity.get_quantity() to validate the returned MechPart's quantity is correct, however i am getting very large numbers for some reason. What is also confusing me is that in the MechPart constructor it assigns a value of 0 to quantity.
Eventually the updateFromFile() function gives me a segmentation fault, so something is very wrong here but I can't work out what as yet.

Answer 1

Recursive functions need to return their recursive calls back up to their caller for them to work properly. Look at the classic factorial example of recursion:
int factorial(int n) {
if (n == 1) {
return 1;
}
else {
return n*factorial(n-1);
}
}
As others have pointed out, your quantitySearch function only returns q_ptr->data() but never returns the return value from the recursive quantitySearch calls. I would start there and I would strongly suggest adding in cout statements in the recursive function to get a complete picture of what's happening "under the hood"