Thread: Linker Error

This code (from the tutorials) gives me a linker error. I'm using VC++ 6.0

Here's the code:

#include <iostream.h>

struct node
{
int key_value;
node *left;
node *right;
};

class btree
{
node *root;
btree();
~btree();
void destroy_tree(node *leaf);
void insert(int key, node *leaf);
node *search(int key, node *leaf);
public:
void insert(int key);
node *search(int key);
void destroy_tree();
};

btree::btree()
{
root=NULL;
}

btree::~btree()
{
destroy_tree();
}

void destroy_tree(node *leaf)
{
if(leaf!=NULL)
{
destroy_tree(leaf->left);
destroy_tree(leaf->right);
delete leaf;
}
}

void btree::insert(int key, node *leaf)
{
if(key< leaf->key_value)
{
if(leaf->left!=NULL)
insert(key, leaf->left);
else
{
leaf->left=new node;
leaf->left->key_value=key;
leaf->left->left=NULL; //Sets the left child of the child node to null
leaf->left->right=NULL; //Sets the right child of the child node to null
}
}
else if(key>=leaf->key_value)
{
if(leaf->right!=NULL)
insert(key, leaf->right);
else
{
leaf->right=new node;
leaf->right->key_value=key;
leaf->right->left=NULL; //Sets the left child of the child node to null
leaf->right->right=NULL; //Sets the right child of the child node to null
}
}
}

node *btree::search(int key, node *leaf)
{
if(leaf!=NULL)
{
if(key==leaf->key_value)
return leaf;
if(key<leaf->key_value)
return search(key, leaf->left);
else
return search(key, leaf->right);
}
else return NULL;
}

void btree::insert(int key)
{
if(root!=NULL)
insert(key, root);
else
{
root=new node;
root->key_value=key;
root->left=NULL;
root->right=NULL;
}
}

node *btree::search(int key)
{
return search(key, root);
}

void btree::destroy_tree()
{
destroy_tree(root);
}

void main()
{
cout << "yeah"
}

and here's the error:

--------------------Configuration: search a tree - Win32 Debug--------------------
Compiling...
source.cpp
Linking...
source.obj : error LNK2001: unresolved external symbol "private: void __thiscall btree::destroy_tree(struct node *)" (?destroy_tree@btree@@AAEXPAUnode@@@Z)
Debug/search a tree.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

search a tree.exe - 2 error(s), 0 warning(s)

thanks.

unresolved external errord are fun...... b/c they don't tell you where the problem is generated,
Your Linker flags an error if your source code cannot be linked (attached) together, a lot of times it happens if you have few separete source files and start including one in the other....

There aren't any other files.

I just noticed an error, and it's not the one causing it, but it's the cout line in the main function. There isn't a ; at the end.

<code>
#include <iostream.h>

struct node
{
int key_value;
node *left;
node *right;
};

class btree
{
node *root;
btree();
~btree();
void destroy_tree(node *leaf);
void insert(int key, node *leaf);
node *search(int key, node *leaf);
public:
void insert(int key);
node *search(int key);
void destroy_tree();
};

btree::btree()
{
root=NULL;
}

btree::~btree()
{
destroy_tree();
}

void destroy_tree(node *leaf)
{
if(leaf!=NULL)
{
destroy_tree(leaf->left);
destroy_tree(leaf->right);
delete leaf;
}
}

void btree::insert(int key, node *leaf)
{
if(key< leaf->key_value)
{
if(leaf->left!=NULL)
insert(key, leaf->left);
else
{
leaf->left=new node;
leaf->left->key_value=key;
leaf->left->left=NULL; //Sets the left child of the child node to null
leaf->left->right=NULL; //Sets the right child of the child node to null
}
}
else if(key>=leaf->key_value)
{
if(leaf->right!=NULL)
insert(key, leaf->right);
else
{
leaf->right=new node;
leaf->right->key_value=key;
leaf->right->left=NULL; //Sets the left child of the child node to null
leaf->right->right=NULL; //Sets the right child of the child node to null
}
}
}

node *btree::search(int key, node *leaf)
{
if(leaf!=NULL)
{
if(key==leaf->key_value)
return leaf;
if(key<leaf->key_value)
return search(key, leaf->left);
else
return search(key, leaf->right);
}
else return NULL;
}

void btree::insert(int key)
{
if(root!=NULL)
insert(key, root);
else
{
root=new node;
root->key_value=key;
root->left=NULL;
root->right=NULL;
}
}

node *btree::search(int key)
{
return search(key, root);
}

void btree::destroy_tree()
{
destroy_tree(root);
}

void main()
{

}
</code>