fatal error LNK1120: 2 unresolved externals错误 帮忙看看

#include "stdafx.h"
#include<iostream.h>

const int defaultSize = 100;

class LinearList
{
public:
// LinearList();
// ~LinearList();
virtual int Size()const = 0;
virtual int Length()const = 0;
virtual int Locate(int i)const = 0;
virtual int Search(int&x)const = 0;
virtual bool getData(int i,int& x)const = 0 ;
virtual bool setData(int i,int& x) = 0;
virtual bool Insert(int i,int& x) = 0;
virtual bool Remove(int i,int& x) = 0;
virtual bool IsEmpty()const = 0;
virtual bool IsFull()const = 0;
virtual void Sort() = 0;
virtual void input() = 0;
virtual void output() = 0;
// virtual LinearList operator=(LinearList& L) = 0;

};
struct LinkNode
{
int data;
LinkNode* link;
LinkNode (LinkNode * ptr = NULL){link = ptr;}
LinkNode(const int item,LinkNode * ptr = NULL)
{data = item;link = ptr;}
};
<

error LNK2001 fatal error LNK1120 fatal error LNK1120: 4 unresolved externals Fatal error FATAL ERROR错误 FATAL ERROR是什么错误？ autocad r14 fatal error VC fatal error C1070 VC++: fatal error C1189 FATAL ERROR 浩方魔兽! stop: c000021a {fatal system error}