LNK1120 and LNK2001 "unresolved external symbol error _mainCRTStartup"

[Jetsetivan]

Hi everyone,

For practice I am trying to code a simplified version of the template "std::list" but have come accross the LNK1120 + LNK2001 errors.

After looking in Visual Studio's documentation and some investigation, it seems the two most common causes are: 1) invalid calls in the code to things which don't exist, or 2) invalid project settings.

I can't seem to find any of these two problems in my code/project. On the other hand, I have also heard that these errors may be the result of some limitation in C++ where one template cannot call another one defined outside the calling header file, but I'm not sure about this last one.

In any case, I would really appreciate if someone could take a look at the following code and give me a hand. Thanks!

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

#include <iostream>
#include <string>
#include "Linked Node 13_9_1.h"

using namespace std;

template <typename T>
class LinkedList
{
public:
	LinkedList();
	~LinkedList();
	LinkedList(const LinkedList& rhs);

	void append(T copieddata);
	void printlist();
	void destroy();

private:
	LinkedNode* mFirst;
	LinkedNode* mLast;
};

template <typename T>
LinkedList<T>::LinkedList()
{
	mFirst = 0;
	mLast= 0;
}

template <typename T>
LinkedList<T>::~LinkedList()
{
	destroy();
}

template <typename T>
void LinkedList<T>::destroy()
{
	if (mFirst != 0 )
	{
		LinkedNode<T>* current = mFirst;
		while ( current != 0 )
		{
			LinkedNode<T>* oldnode = current;
			current = current->next;
			delete oldnode;
			oldnode = 0;
		}
	}
}

template <typename T>
void LinkedList<T>::printlist()
{
		LinkedNode<T>* current = mFirst;
		while ( current != 0 )
		{
			cout << current->data << " ";
			current = current->next;
		}
}

template <typename T>
void LinkedList<T>::append(T copieddata)
{
	LinkedNode<T>* newNode = new LinkedNode<T>;
	newNode->data = copieddata;
	if ( mFirst == 0 )
	{	
		mFirst = newNode;		mLast = newNode;
		newNode->next = 0;		newNode->prev = 0;
	}
	else 
	{	
		newNode->prev = mLast;	mLast = newNode;
		newNode->next = 0;		newNode->prev->next = newNode;
	}
}

template <typename T>
LinkedList<T>::(const LinkedList& rhs)
{
	if ( rhs.mFirst != 0)
	{
		append(rhs.mFirst->data);
		LinkedNode<T>* index = rhs.mFirst->next;
		while ( index != 0)
		{
			append(index->data);
			index = index->next;
		}
	}
}
		
#endif // LINKEDLIST_H

[Jetsetivan]

I seemed to have figured it out, C++ doesn't seem to like compiling header files alone (at least in terms of templates perhaps). I implemented a test source file with it and now it compiles fine.

Now, however, I have another problem (of course!): I run accross the following assertion failure after running the program in debug :

_BLOCK_TYPE_IS_VALID(pHead -> NBlockUse)

Although my test .cpp isn't shown here, in it I simply instantiate an object of LinkedList with the default constructor (which works fine).

On the other hand, I then instantiate another object using the class's copy constructor and it creates this error, any ideas?

Thanks to all,
Ivan

[Salem]

> On the other hand, I then instantiate another object using the class's copy constructor and it creates this error, any ideas?
You don't initialise mFirst in the current object before trying to append.

[Jetsetivan]

You're absolutely right I forgot to initialize, thanks for the tip :) I added mFirst = 0 and mLast= 0. The error, however, still persists.

I read that this may have to do with trying to delete a dyn mem allocation that was already deleted, but I don't see any problem with my destroy() routine....

[Salem]

What T are you using as the type for your list?

If it's a class, and it lacks a copy constructor, then your internal assignments are broken (when you copy the data)

[Jetsetivan]

What T are you using as the type for your list?

If it's a class, and it lacks a copy constructor, then your internal assignments are broken (when you copy the data)

Very true, for now I just designed the class to take simple types (i.e. chars, ints, floats....). Here's the source file for testing the template:

// TEST program for "Linked Node" & "Linked List"

#include <iostream>
#include <string>
#include "Linked List 13_9_1.h"

using namespace std;

int main()
{
	cout << "Creating a linked list of INTs with 5 elements:\n";
	LinkedList<int> tList;

	tList.append(3);
	tList.append(5);
	tList.append(7);
	tList.append(9);
	tList.append(11);
	tList.append(13);

	cout << "\nOutputting list: ";
	tList.printlist();

	cout << "\nCreating new list based on old list:\n";
	LinkedList<int> newList(tList);
	cout << "\nOutputting list: ";
	newList.printlist();
}