使用memset要小心

iteye_4515

于 2008-12-17 21:12:00 发布

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本文记录了一次程序重构后出现的 CString 析构函数断言失败问题，通过分析发现构造函数中不当使用 memset 导致 CString 的 m_pchData 成员变量被置为 NULL，最终引发析构时的断言失败。

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<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta name="ProgId" content="Word.Document"> <meta name="Generator" content="Microsoft Word 12"> <meta name="Originator" content="Microsoft Word 12"> <link rel="File-List" href="file:///C:%5CDOCUME%7E1%5CADMINI%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_filelist.xml"> <link rel="themeData" href="file:///C:%5CDOCUME%7E1%5CADMINI%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_themedata.thmx"> <link rel="colorSchemeMapping" href="file:///C:%5CDOCUME%7E1%5CADMINI%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_colorschememapping.xml"> <smallfrac m:val="off"><dispdef><lmargin m:val="0"><rmargin m:val="0"><defjc m:val="centerGroup"><wrapindent m:val="1440"><intlim m:val="subSup"><narylim m:val="undOvr"></narylim></intlim></wrapindent><style>  </style> <span style="font-size: 10.5pt; font-family: 宋体;">今天把程序重构了。运行一下，没想到程序到了退出的时候触发了一个</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">ASSERT</span><span style="font-size: 10.5pt; font-family: 宋体;">。看看栈信息，运行到了</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">CString</span><span style="font-size: 10.5pt; font-family: 宋体;">的析构函数：</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US"><br style=""><div class="highlighter"><ol class="highlighter-cpp" start="1"> <li><span>CString::~CString()</span></li> <li class="alt"> <span></span><span class="comment">//freeanyattacheddata</span><span></span> </li> <li><span>{</span></li> <li class="alt"> <span></span><span class="keyword">if</span><span>(GetData()!=_afxDataNil)</span> </li> <li><span>{</span></li> <li class="alt"> <span></span><span class="keyword">if</span><span>(InterlockedDecrement(&GetData()->nRefs)<=0)</span> </li> <li><span>FreeData(GetData());</span></li> <li class="alt"><span>}</span></li> <li><span>}</span></li> <li class="alt"> <span></span><br> </li> <li> <span>_AFX_INLINECStringData*CString::GetData()</span><span class="keyword">const</span><span></span> </li> <li class="alt"> <span>{ASSERT(m_pchData!=NULL);</span><span class="keyword">return</span><span>((CStringData*)m_pchData)-1;}</span> </li> <li> <span></span><br> </li> <li class="alt"> <span></span><span class="keyword">class</span><span>ImageItem</span> </li> <li><span>{</span></li> <li class="alt"> <span></span><span class="keyword">public</span><span>:</span> </li> <li><span>ImageItem();</span></li> <li class="alt"><span>~ImageItem();</span></li> <li> <span>unsigned</span><span class="datatypes">int</span><span>id;</span> </li> <li class="alt"> <span>unsigned</span><span class="datatypes">int</span><span>x;</span> </li> <li> <span>unsigned</span><span class="datatypes">int</span><span>y;</span> </li> <li class="alt"><span>CStringfilename;</span></li> <li> <span></span><span class="datatypes">HDC</span><span>hdc;</span> </li> <li class="alt"><span>BITMAPbmp;</span></li> <li> <span></span><span class="datatypes">HBITMAP</span><span>hbmp;</span> </li> <li class="alt"> <span></span><span class="datatypes">HBITMAP</span><span>hOldBmp;</span> </li> <li><span>};</span></li> <li class="alt"> <span></span><span class="keyword">class</span><span>ImageList</span> </li> <li><span>{</span></li> <li class="alt"> <span></span><span class="keyword">public</span><span>:</span> </li> <li><span>ImageList();</span></li> <li class="alt"><span>~ImageList();</span></li> <li><span>ImageItemimages[128];</span></li> <li class="alt"> <span></span><span class="datatypes">int</span><span>m_imageCount;</span> </li> <li><span>};</span></li> <li class="alt"> <span></span><br> </li> <li><span>ImageList::ImageList()</span></li> <li class="alt"><span>{</span></li> <li> <span>memset(images,0,</span><span class="keyword">sizeof</span><span>(images));</span> </li> <li class="alt"><span>m_imageCount=0;</span></li> <li><span>}</span></li> <li class="alt"> <span></span><br> </li> </ol></div></span><meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta name="ProgId" content="Word.Document"> <meta name="Generator" content="Microsoft Word 12"> <meta name="Originator" content="Microsoft Word 12"> <link rel="File-List" href="file:///C:%5CDOCUME%7E1%5CADMINI%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_filelist.xml"> <link rel="themeData" href="file:///C:%5CDOCUME%7E1%5CADMINI%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_themedata.thmx"> <link rel="colorSchemeMapping" href="file:///C:%5CDOCUME%7E1%5CADMINI%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_colorschememapping.xml"> <smallfrac m:val="off"><dispdef><lmargin m:val="0"><rmargin m:val="0"><defjc m:val="centerGroup"><wrapindent m:val="1440"><intlim m:val="subSup"><narylim m:val="undOvr"></narylim></intlim></wrapindent><style>  </style> <span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">m_pchData</span><span style="font-size: 10.5pt; font-family: 宋体;">竟然等于</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">NULL</span><span style="font-size: 10.5pt; font-family: 宋体;">，怎么想也不明白。然后找新春帮忙看，原来是</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">ImageList</span><span style="font-size: 10.5pt; font-family: 宋体;">的构造函数里将</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">CString</span><span style="font-size: 10.5pt; font-family: 宋体;">给</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US">memset</span><span style="font-size: 10.5pt; font-family: 宋体;">了，编译期自然不会报错，而这个错误到了析构的时候才被发现。真是搞笑。看来以后要memset的时候要小心点。</span><span style='font-size: 10.5pt; font-family: "Calibri","sans-serif";' lang="EN-US"><br style=""><br style=""></span></defjc></rmargin></lmargin></dispdef></smallfrac></defjc></rmargin></lmargin></dispdef></smallfrac>

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