subject_61919.htm

vc

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序号：61919 发表者：lixiaofei 发表日期：2003-11-23 10:29:36
<br>主题：请教各位高手：为什么在VC.net中这句话throw new CException;通不过？
<br>内容：这是书中的源代码，在VC6+XP下通过<BR>VC.net中出错提示为： f:\图形图像\ch08\demo_viewdib\cdib.cpp(438): error C2259: “CException” : 不能实例化抽象类<BR><BR>/////////////////////////////////////////////<BR>//这个函数从文件中将DIB读进CDib对象中，文件<BR>//被成功的打开。<BR>//参数<BR>//pFile：指向包含DIB文件的指针<BR>////////////////////////////////////////////<BR>BOOL CDib::ReadFile(CFile* pFile)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;//读文件头得到BITMAPINFOHEADER和颜色表的大小<BR>&nbsp;&nbsp;&nbsp;&nbsp;//读BITMAPINFOHEADER得到图像小、尺寸和颜色表<BR>&nbsp;&nbsp;&nbsp;&nbsp;//读取图像信息<BR>&nbsp;&nbsp;&nbsp;&nbsp;InitDestroy();<BR>&nbsp;&nbsp;&nbsp;&nbsp;int counts, size;<BR>&nbsp;&nbsp;&nbsp;&nbsp;BITMAPFILEHEADER bmfh;<BR>&nbsp;&nbsp;&nbsp;&nbsp;try {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counts = pFile-&gt;Read((LPVOID) &amp;bmfh, <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sizeof(BITMAPFILEHEADER));<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if(counts != sizeof(BITMAPFILEHEADER)) {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;throw new CException;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if(bmfh.bfType != 0x4d42) {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;throw new CException;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;size = bmfh.bfOffBits - sizeof(BITMAPFILEHEADER);<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m_lpBMPHdr = (LPBITMAPINFOHEADER) new char[size];<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// BITMAPINFOHEADER和颜色表<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counts = pFile-&gt;Read(m_lpBMPHdr, size); <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ComputeImage();<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ComputePaletteSize(m_lpBMPHdr-&gt;biBitCount);<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;SetWinPalette();<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m_lpDIBits = (LPBYTE) new char[m_dwImageSize];<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counts = pFile-&gt;Read(m_lpDIBits, m_dwImageSize); <BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;catch(CException* pe) {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;AfxMessageBox(&#34;Read error&#34;);<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pe-&gt;Delete();<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return FALSE;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;return TRUE;<BR>}
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<font color=red>答案被接受</font><br>回复者：红苹果 回复日期：2003-11-23 11:31:25
<br>内容：CException在VC.net已经是一个抽象类，不能直接定义其对象，必须使用它的派生类来定义对象。比如，对于文件操作应该用CFileException* pe<BR><BR>所谓抽象类就是类中含有纯虚函数的类，也就是有虚函数被申明了，但没有被定义，如：<BR>virtual void dump( )=0;<BR>就是一个纯虚函数，申明该函数的类就是抽象类，这种类只能作为基类，不能直接使用。
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回复者：lixiaofei 回复日期：2003-11-23 17:48:58
<br>内容：谢谢你！另外再向你请教两个问题，望不吝赐教<BR>1〉编译警告<BR>在BOOL CDemo_ViewDibApp::InitInstance()中，下面的语句为什么有问题<BR>{#ifdef _AFXDLL<BR>&nbsp;&nbsp;&nbsp;&nbsp;Enable3dControls();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Call this when using MFC in a shared DLL<BR>#else<BR>&nbsp;&nbsp;&nbsp;&nbsp;Enable3dControlsStatic();&nbsp;&nbsp;&nbsp;&nbsp;// Call this when linking to MFC statically<BR>这一句话编译警告：f:\图形图像\ch08\demo_viewdib\demo_viewdib.cpp(60): warning C4996: “CWinApp::Enable3dControlsStatic”被声明为否决的<BR>#endif<BR>2〉编译警告<BR>//存储图像<BR>void CDib::Serialize(CArchive&amp; ar)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;DWORD pos;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pos = ar.GetFile()-&gt;GetPosition();//这一句编译警告<BR>f:\图形图像\ch08\demo_viewdib\cdib.cpp(541): warning C4244: “=” : 从“ULONGLONG”转换到“DWORD”，可能丢失数据<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;TRACE(&#34;CDib::Serialize -- pos = %d\n&#34;, pos);<BR>&nbsp;&nbsp;&nbsp;&nbsp;ar.Flush();<BR>&nbsp;&nbsp;&nbsp;&nbsp;pos = ar.GetFile()-&gt;GetPosition();//这一句编译警告与上一句相同<BR>&nbsp;&nbsp;&nbsp;&nbsp;TRACE(&#34;CDib::Serialize -- pos = %d\n&#34;, pos);<BR>&nbsp;&nbsp;&nbsp;&nbsp;if(ar.IsStoring()) {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;WriteFile(ar.GetFile());//WriteFile（）自定义的函数<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ReadFile(ar.GetFile());<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>}
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回复者：红苹果 回复日期：2003-11-23 18:35:11
<br>内容：1.<BR>{#ifdef _AFXDLL<BR>&nbsp;&nbsp;&nbsp;&nbsp;Enable3dControls();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Call this when using MFC in a shared DLL<BR>#else<BR>&nbsp;&nbsp;&nbsp;&nbsp;Enable3dControlsStatic();&nbsp;&nbsp;&nbsp;&nbsp;// Call this when linking to MFC statically<BR>这一句话编译警告：f:\图形图像\ch08\demo_viewdib\demo_viewdib.cpp(60): warning C4996: “CWinApp::Enable3dControlsStatic”被声明为否决的<BR>#endif<BR><BR>在VC.NET的新版MFC中改动较多，同样VC.NET已经不支持Enable3dControls或Enable3dControlsStatic函数，具体我也不清楚，你查查MSDN,我机器上没有.NET.不过这个警告可以不管。<BR><BR>2.<BR>&nbsp;&nbsp;&nbsp;&nbsp;pos = ar.GetFile()-&gt;GetPosition();//这一句编译警告<BR>f:\图形图像\ch08\demo_viewdib\cdib.cpp(541): warning C4244: “=” : 从“ULONGLONG”转换到“DWORD”，可能丢失数据<BR><BR>为了管理更大的文件，新版MFC的CFile的文件参数都是64为的了，GetPosition返回的是一个64位的无符号整型，而DWORD只是一个32位的无符号整型。这个警告可以不予理睬，只要你的文件不大于4GByte.
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回复者：lixiaofei 回复日期：2003-11-24 19:47:44
<br>内容：谢谢你，红苹果，你知道的真多，以后还望你继续多指导指导！
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