帮忙看下这个类多次调用是否有问题
class CMemDCEx : public CDC
{
public:
CMemDCEx(CDC* pDC, const CRect* pRect = NULL, BOOL transparent = FALSE)
{
ASSERT(pDC != NULL);

m_pDC = pDC;
m_pOldBitmap = NULL;
m_bMemDC = !pDC->IsPrinting();

// get the rectangle to draw
if (pRect == NULL)
{
pDC->GetClipBox(&m_rect);
}
else
{
m_rect = *pRect;
}
BOOL bRight = TRUE;
if (m_bMemDC)
{
// create a memory DC
CreateCompatibleDC(pDC);
pDC->LPtoDP(&m_rect);

bRight = m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());

if (bRight)
{
m_pOldBitmap = SelectObject(&m_bitmap);

SetMapMode(pDC->GetMapMode());
pDC->DPtoLP(&m_rect);
SetWindowOrg(m_rect.left, m_rect.top);
}
else
{
int iCount = 0;
}
}
else
{
// make a copy of the relevent parts of the current DC for printing
m_bPrinting = pDC->m_bPrinting;
m_hDC = pDC->m_hDC;
m_hAttribDC = pDC->m_hAttribDC;
}

SetBkMode(TRANSPARENT);

// fill background
if (transparent)
{
BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(), m_pDC, 0, 0, SRCCOPY);
}
else
{
FillSolidRect(m_rect, pDC->GetBkColor()); // not needed in OPAQUE mode?
}
}

~CMemDCEx()
{
if (m_bMemDC)
{
// copy the offscreen bitmap onto the screen
m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
this, m_rect.left, m_rect.top, SRCCOPY);

// swap back the original bitmap
SelectObject(m_pOldBitmap);
}
else
{
// all we need to do is replace the DC with an illegal value, this keeps us from accidently
// deleting the handles associated with the CDC that was passed to the constructor
m_hDC = m_hAttribDC = NULL;
}
}

private:
CBitmap m_bitmap; // offscreen bitmap
CBitmap* m_pOldBitmap; // bitmap originally found in CMemDCEx
CDC* m_pDC; // saves CDC passed in constructor
CRect m_rect; // rectangle of drawing area
BOOL m_bMemDC; // TRUE if CDC really is a Memory DC
};

[解决办法]
怎样多次调用？
如果需要多次绘图，把方法从构造函数和析构函数中提取出来，弄成成员函数
[解决办法]
我也有个：

C/C++ code

#if !defined(AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_)#define AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_#if _MSC_VER >= 1000#pragma once#endif // _MSC_VER >= 1000// MemDC.h : header file////////////////////////////////////////////////////// CMemDC - memory DC//// Author: Keith Rule// Email:  keithr@europa.com// Copyright 1996-1997, Keith Rule//// You may freely use or modify this code provided this// Copyright is included in all derived versions.//// History - 10/3/97 Fixed scrolling bug.//                   Added print support.//           25 feb 98 - fixed minor assertion bug//// This class implements a memory Device Contextclass CMemDC : public CDC{public:    // constructor sets up the memory DC    CMemDC(CDC* pDC) : CDC()    {        ASSERT(pDC != NULL);        m_pDC = pDC;        m_pOldBitmap = NULL;#ifndef _WIN32_WCE_NO_PRINTING        m_bMemDC = !pDC->IsPrinting();#else        m_bMemDC = FALSE;#endif        if (m_bMemDC)    // Create a Memory DC        {            pDC->GetClipBox(&m_rect);            CreateCompatibleDC(pDC);            m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());            m_pOldBitmap = SelectObject(&m_bitmap);#ifndef _WIN32_WCE            SetWindowOrg(m_rect.left, m_rect.top);#endif            // EFW - Bug fix - Fill background in case the user has overridden            // WM_ERASEBKGND.  We end up with garbage otherwise.            // CJM - moved to fix a bug in the fix.            FillSolidRect(m_rect, pDC->GetBkColor());        }        else        // Make a copy of the relevent parts of the current DC for printing        {#if !defined(_WIN32_WCE) || ((_WIN32_WCE > 201) && !defined(_WIN32_WCE_NO_PRINTING))            m_bPrinting = pDC->m_bPrinting;#endif            m_hDC       = pDC->m_hDC;            m_hAttribDC = pDC->m_hAttribDC;        }    }    // Destructor copies the contents of the mem DC to the original DC    ~CMemDC()    {        if (m_bMemDC)        {            // Copy the offscreen bitmap onto the screen.            m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),                          this, m_rect.left, m_rect.top, SRCCOPY);            //Swap back the original bitmap.            SelectObject(m_pOldBitmap);        } else {            // All we need to do is replace the DC with an illegal value,            // this keeps us from accidently deleting the handles associated with            // the CDC that was passed to the constructor.            m_hDC = m_hAttribDC = NULL;        }    }    // Allow usage as a pointer    CMemDC* operator->() {return this;}            // Allow usage as a pointer    operator CMemDC*() {return this;}private:    CBitmap  m_bitmap;      // Offscreen bitmap    CBitmap* m_pOldBitmap;  // bitmap originally found in CMemDC    CDC*     m_pDC;         // Saves CDC passed in constructor    CRect    m_rect;        // Rectangle of drawing area.    BOOL     m_bMemDC;      // TRUE if CDC really is a Memory DC.};///////////////////////////////////////////////////////////////////////////////{{AFX_INSERT_LOCATION}}// Microsoft Developer Studio will insert additional declarations immediately before the previous line.#endif // !defined(AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_) 
 
[解决办法]
和你多次调用没关系吧
[解决办法]
有严重的内存泄漏吧
1.DeleteObject的使用
2.注意ReleaseDC和DeleteDC的使用