GetTickCount函数为啥总是返回0 ？

直接贴代码：
C/C++ code

void CframeDlg::OnBnClickedButtonFrame()
{
      m_Time_Start=GetTickCount();

    CDC* pDC=GetDlgItem(IDC_PLAYERXCTRL1)->GetWindowDC();
    HDC  m_hDC=pDC->GetSafeHdc();
    Screen2IplImage(m_hDC,"E://监控录像//xiaowenchao.bmp",m_Width,m_Height);
    ReleaseDC(pDC);
    DrawPic2hDC(m_Frame, IDC_STATIC_SHOWIMAGE);

    for(int i=0;i<10000;i++){}

    m_Time_End=GetTickCount();
    CString time_consumed;
    m_Time_Consumed=m_Time_End-m_Time_Start;
    time_consumed.Format("%d",m_Time_Consumed);
    MessageBox(time_consumed);
}

其中
C/C++ code

public:
    DWORD m_Time_Start;
public:
    DWORD m_Time_End;
public:
    DWORD m_Time_Consumed;

已经定义为成员变量，且 m_Time_Start=GetTickCount();已经在oninitialdlg（）中初始化，m_Time_End初始化为0；
但是MessageBox（）每次弹出0（经常是这个值）或者15、16。
请大家帮忙~

论坛对此问题解释如下：

What might be happening is that your program runs too fast for it to update, due to its limited resolution.

You can debug the problem by putting a call to Sleep before the second GetTickCount, to see if the difference is now not 0. 

补充一下，GetTickCount并不准确，建议改用timeGetTime。
C/C++ code

DWORD timeGetTime(void);

m_Time_Start=GetTickCount();
和
m_Time_End=GetTickCount();
之间耗时太少，正常的
加大循环延时就看出效果了
for(int i=0;i<10000000;i++){}
在我机器上 才看出效果来