帮忙看下这个类多次调用是否有问题

[xfxfxy]

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
};

[ouyh12345]

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

[xfxfxy]

我在别的地方直接定义一个临时变量来使用这个类的。
可是多次调用后，会在
bRight = m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
bRight = false 了。
bRight是调试时添加的变量。我想确认下为什么会出现false这种情况。如何解决掉？
是不是使用SelectObject()有问题，需要做其它操作？

[xfxfxy]

我在别的地方直接定义一个临时变量来使用这个类的---描述错误。
---------------
定义一个临时变量：为类的对象。

[schlafenhamster]

我也有个：

#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:  [e-mail]
// 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 Context

class 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_)

你比较比较看看

[写不动代码的人]

和你多次调用没关系吧

[傻X]

有严重的内存泄漏吧
1.DeleteObject的使用
2.注意ReleaseDC和DeleteDC的使用

[xfxfxy]

6楼能否明示如何解决这个问题？
这个的确是存在内存泄露的问题，我觉得程序挂掉还有个原因：有什么资源使用了没有回收的问题。

[xfxfxy]

4楼的这个也有同样的问题，

[xfxfxy]

感谢各位的帮助，问题已经解决。不是这个类的问题。
是上层的问题。上层在构造里使用了new,在析构使用的del，可是一直没有调用析构才导致程序挂掉。