提示 error LNK2001: 无法解析的外部符号 "class Linklist link" (?link@@3VLinklist@@

struct node
{
    CString num,name,photo;
    node *next;
};
class Linklist
{
private:
    node *p;
public:
    node *head;
    Linklist();
    bool add(CString a,CString b);
    bool add(CString a,CString b,CString c);
    bool del(CString a);
    bool del(CString a,CString b);
    node* find(CString a);
    node* find(CString a,CString b);
    bool change(CString a,CString b,CString c);
};


#include "stdafx.h"
#include"linklist.h"
Linklist::Linklist()
{
    head=new node;
    head->next=NULL;
}
node* Linklist::find(CString a)
{
    node *p;
    for(p=head->next;p!=NULL;p=p->next)
    {
        if(p->num==a) return p;
    }
    return p;
}
node* Linklist::find(CString a,CString b)
{
    node *p;
    for(p=head->next;p!=NULL;p=p->next)
    {
        if(p->name==b) return p;
    }
    return p;
}
bool Linklist::add(CString a, CString b)
{
    node *p=find(a);
    if(p!=NULL) return 0;
    else
    {
        node *q=new node;
        q->next=head->next;
        head->next=q;
        q->num=a;
        q->name=b;
        return 1;
    }
}
bool Linklist::add(CString a, CString b,CString c)
{
    node *p=find(a);
    if(p!=NULL) return 0;
    else
    {
        node *q=new node;
        q->next=head->next;
        head->next=q;
        q->num=a;
        q->name=b;
        q->photo=c;
        return 1;
    }
}
bool Linklist::del(CString a)
{
    node *p,*q;
    for(p=head->next,q=head;p!=NULL;p=p->next,q=q->next)
    {
        if(p->num==a)
        {
            q->next=p->next;
            delete p;
            return 1;
        }
    }
    return 0;
}
bool Linklist::del(CString a, CString b)
{
    node *p,*q;
    for(p=head->next,q=head;p!=NULL;p=p->next,q=q->next)
    {
        if(p->name==b)
        {
            q->next=p->next;//MessageBox(NULL,_T("ok"),_T("ok"),MB_ICONWARNING);
            delete p;
            return 1;
        }
    }
    return 0;
}
bool Linklist::change(CString a, CString b, CString c)
{
    node *p=find(a);
    if(p==NULL) return 0;
    else
    {
        p->num=a;
        p->name=b;
        p->photo=c;
        return 1;
    }
}


// bhtDlg.cpp : 实现文件
//
#include "stdafx.h"
#include "bht.h"
#include "bhtDlg.h"
#include "linklist.h"
extern Linklist link;
#ifdef _DEBUG
#define new DEBUG_NEW
#endif

// 用于应用程序“关于”菜单项的CAboutDlg 对话框
class CAboutDlg : public CDialog
{
public:
    CAboutDlg();
// 对话框数据
    enum { IDD = IDD_ABOUTBOX };
    protected:
    virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV 支持
// 实现
protected:
    DECLARE_MESSAGE_MAP()
};
CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
}
void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
    CDialog::DoDataExchange(pDX);
}
BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
END_MESSAGE_MAP()

// CbhtDlg 对话框


CbhtDlg::CbhtDlg(CWnd* pParent /*=NULL*/)
    : CDialog(CbhtDlg::IDD, pParent)
    , t_num(_T(""))
    , t_photo(_T(""))
    , t_name(_T(""))
{
    m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}
void CbhtDlg::DoDataExchange(CDataExchange* pDX)
{
    CDialog::DoDataExchange(pDX);
    DDX_Text(pDX, IDC_EDIT1, t_num);
    DDV_MaxChars(pDX, t_num, 100);
    DDX_Text(pDX, IDC_EDIT3, t_photo);
    DDX_Text(pDX, IDC_EDIT2, t_name);
    DDX_Control(pDX, IDC_LIST1, x_list);
    DDX_Control(pDX, IDC_photo, m_photo);
}
BEGIN_MESSAGE_MAP(CbhtDlg, CDialog)
    ON_WM_SYSCOMMAND()
    ON_WM_PAINT()
    ON_WM_QUERYDRAGICON()
    //}}AFX_MSG_MAP
    ON_BN_CLICKED(IDC_BUTTON2, &CbhtDlg::OnBnClickedButton2)
    ON_BN_CLICKED(IDC_BUTTON3, &CbhtDlg::OnBnClickedButton3)
    ON_BN_CLICKED(IDC_BUTTON4, &CbhtDlg::OnBnClickedButton4)
    ON_BN_CLICKED(IDC_BUTTON5, &CbhtDlg::OnBnClickedButton5)
    ON_BN_CLICKED(IDC_BUTTON1, &CbhtDlg::OnBnClickedButton1)
END_MESSAGE_MAP()

// CbhtDlg 消息处理程序
BOOL CbhtDlg::OnInitDialog()
{
    CDialog::OnInitDialog();
    // 将“关于...”菜单项添加到系统菜单中。
    DWORD dwStyle = x_list.GetExtendedStyle();
    dwStyle |= LVS_EX_FULLROWSELECT;//选中某行使整行高亮（只适用与report风格的listctrl）
    dwStyle |= LVS_EX_GRIDLINES;//网格线（只适用与report风格的listctrl）
    x_list.SetExtendedStyle(dwStyle); //设置扩展风格
    x_list.InsertColumn(0,"学号",LVCFMT_LEFT,95,0);
    x_list.InsertColumn(1,"姓名",LVCFMT_LEFT,85,1);
    // IDM_ABOUTBOX 必须在系统命令范围内。
    ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
    ASSERT(IDM_ABOUTBOX < 0xF000);
    CMenu* pSysMenu = GetSystemMenu(FALSE);
    if (pSysMenu != NULL)
    {
        CString strAboutMenu;
        strAboutMenu.LoadString(IDS_ABOUTBOX);
        if (!strAboutMenu.IsEmpty())
        {
            pSysMenu->AppendMenu(MF_SEPARATOR);
            pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
        }
    }
    // 设置此对话框的图标。当应用程序主窗口不是对话框时，框架将自动
    //  执行此操作
    SetIcon(m_hIcon, TRUE);            // 设置大图标
    SetIcon(m_hIcon, FALSE);        // 设置小图标
    // TODO: 在此添加额外的初始化代码
    return TRUE;  // 除非将焦点设置到控件，否则返回TRUE
}
void CbhtDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
    if ((nID & 0xFFF0) == IDM_ABOUTBOX)
    {
        CAboutDlg dlgAbout;
        dlgAbout.DoModal();
    }
    else
    {
        CDialog::OnSysCommand(nID, lParam);
    }
}
// 如果向对话框添加最小化按钮，则需要下面的代码
//  来绘制该图标。对于使用文档/视图模型的MFC 应用程序，
//  这将由框架自动完成。
void CbhtDlg::OnPaint()
{
    if (IsIconic())
    {
        CPaintDC dc(this); // 用于绘制的设备上下文
        SendMessage(WM_ICONERASEBKGND, reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);
        // 使图标在工作区矩形中居中
        int cxIcon = GetSystemMetrics(SM_CXICON);
        int cyIcon = GetSystemMetrics(SM_CYICON);
        CRect rect;
        GetClientRect(&rect);
        int x = (rect.Width() - cxIcon + 1) / 2;
        int y = (rect.Height() - cyIcon + 1) / 2;
        // 绘制图标
        dc.DrawIcon(x, y, m_hIcon);
    }
    else
    {
        CDialog::OnPaint();
    }
}
//当用户拖动最小化窗口时系统调用此函数取得光标
//显示。
HCURSOR CbhtDlg::OnQueryDragIcon()
{
    return static_cast<HCURSOR>(m_hIcon);
}

void CbhtDlg::OnBnClickedButton2()
{
    // TODO: 在此添加控件通知处理程序代码'
    UpdateData(true);
    if(t_num.IsEmpty()) MessageBox("学号不能为空","错误",MB_ICONWARNING);
    else if(t_name.IsEmpty()) MessageBox("姓名不能为空","错误",MB_ICONWARNING);
    else if(t_photo.IsEmpty())
    {
        if(link.add(t_num,t_name))
        {
            x_list.InsertItem(0,t_num);
            x_list.SetItemText(0,1,t_name);
        }
        else MessageBox("该数据已存在","错误",MB_ICONWARNING);
    }
    else
    {
        if(link.add(t_num,t_name,t_photo))
        {
            x_list.InsertItem(0,t_num);
            x_list.SetItemText(0,1,t_name);
        }
        else MessageBox("该数据已存在","错误",MB_ICONWARNING);
    }
    UpdateData(false);
}
void CbhtDlg::OnBnClickedButton3()
{
    // TODO: 在此添加控件通知处理程序代码
    UpdateData(true);
    if(t_num.IsEmpty()) MessageBox("学号不能为空","错误",MB_ICONWARNING);
    else if(t_name.IsEmpty()) MessageBox("姓名不能为空","错误",MB_ICONWARNING);
    else
    {
        if(link.del(t_num,t_name))
        {
            MessageBox("删除成功");
            for(int i=0;;i++)
                if(x_list.GetItemText(i,0)==t_num) {x_list.DeleteItem(i);break;}
        }
        else MessageBox("该数据不存在","错误",MB_ICONWARNING);
    }
    UpdateData(false);
}
void CbhtDlg::OnBnClickedButton4()
{
    // TODO: 在此添加控件通知处理程序代码
    UpdateData(true);
    node *p;
    if(!t_num.IsEmpty()) p=link.find(t_num);
    else if(!t_name.IsEmpty()) p=link.find(t_num,t_name);
    else {MessageBox("学号和姓名不能全为空","提示");return;}
    if(p==NULL) MessageBox("没有找到该数据","提示");
    else
    {
        t_num=p->num;t_name=p->name;t_photo=p->photo;
        if(!t_photo.IsEmpty()) photo_show();
    }
    UpdateData(false);
}
void CbhtDlg::OnBnClickedButton5()
{
    // TODO: 在此添加控件通知处理程序代码
    UpdateData(true);
    if(!t_name.IsEmpty()&&!t_num.IsEmpty())
    {
        if(link.change(t_num,t_name,t_photo))
        {
            MessageBox("修改成功","提示");
            for(int i=0;;i++)
                if(x_list.GetItemText(i,0)==t_num)
                {
                    x_list.SetItemText(i,0,t_num);
                    x_list.SetItemText(i,1,t_name);
                    break;
                }
                if(!t_photo.IsEmpty()) photo_show();
        }
        else MessageBox("该学号不存在","错误");
    }
    else {MessageBox("学号或姓名不能为空","提示");return;}
    UpdateData(false);
}
void CbhtDlg::OnBnClickedButton1()
{
    // TODO: 在此添加控件通知处理程序代码
    UpdateData(true);
    CFileDialog m_file(true,"bmp",NULL,NULL,"位图文件(.bmp)|*.bmp",this);
    if(m_file.DoModal()==IDOK)
    {
        CString pathname=m_file.GetPathName();
        t_photo=pathname;
    }
    photo_show();
    UpdateData(false);
}
void CbhtDlg::photo_show()
{
    HBITMAP hbitmap=(HBITMAP)::LoadImage(AfxGetInstanceHandle(),t_photo,IMAGE_BITMAP,0,0,LR_LOADFROMFILE|LR_DEFAULTCOLOR|LR_DEFAULTSIZE);
    m_photo.SetBitmap(hbitmap);
    /*CRect rect,imageRect;
    m_photo.GetWindowRect(imageRect);
    this->GetWindowRect(rect);
    rect.right=imageRect.right+20;
    rect.bottom=imageRect.bottom+20;
    this->MoveWindow(rect);*/
}