subject_45702.htm

来自「一些关于vc的问答」· HTM 代码 · 共 36 行

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序号：45702 发表者：罗兹维尔 发表日期：2003-07-02 23:16:00
<br>主题：重载operator+的疑惑
<br>内容：一半看到书上写的都是带两个参数的<BR>我自己写了一下带一个参数的，也可以阿<BR>不知道带两个好在那里？<BR><BR>MyString&amp; operator+(MyString &amp;str) //我写的
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回复者：擎天柱 回复日期：2003-07-03 08:11:37
<br>内容：参考CString::operator+<BR><BR>// NOTE: "operator+" is done as friend functions for simplicity<BR>//&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;There are three variants:<BR>//&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;CString + CString<BR>// and for ? = TCHAR, LPCTSTR<BR>//&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;CString + ?<BR>//&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;? + CString<BR><BR>void CString::ConcatCopy(int nSrc1Len, LPCTSTR lpszSrc1Data,<BR>&nbsp;&nbsp;&nbsp;&nbsp;int nSrc2Len, LPCTSTR lpszSrc2Data)<BR>{<BR>&nbsp;&nbsp;// -- master concatenation routine<BR>&nbsp;&nbsp;// Concatenate two sources<BR>&nbsp;&nbsp;// -- assume that 'this' is a new CString object<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;int nNewLen = nSrc1Len + nSrc2Len;<BR>&nbsp;&nbsp;&nbsp;&nbsp;if (nNewLen != 0)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;AllocBuffer(nNewLen);<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;memcpy(m_pchData, lpszSrc1Data, nSrc1Len*sizeof(TCHAR));<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;memcpy(m_pchData+nSrc1Len, lpszSrc2Data, nSrc2Len*sizeof(TCHAR));<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>}<BR><BR>CString AFXAPI operator+(const CString&amp; string1, const CString&amp; string2)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;CString s;<BR>&nbsp;&nbsp;&nbsp;&nbsp;s.ConcatCopy(string1.GetData()-&gt;nDataLength, string1.m_pchData,<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;string2.GetData()-&gt;nDataLength, string2.m_pchData);<BR>&nbsp;&nbsp;&nbsp;&nbsp;return s;<BR>}<BR><BR>CString AFXAPI operator+(const CString&amp; string, LPCTSTR lpsz)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;ASSERT(lpsz == NULL || AfxIsValidString(lpsz));<BR>&nbsp;&nbsp;&nbsp;&nbsp;CString s;<BR>&nbsp;&nbsp;&nbsp;&nbsp;s.ConcatCopy(string.GetData()-&gt;nDataLength, string.m_pchData,<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;CString::SafeStrlen(lpsz), lpsz);<BR>&nbsp;&nbsp;&nbsp;&nbsp;return s;<BR>}<BR><BR>CString AFXAPI operator+(LPCTSTR lpsz, const CString&amp; string)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;ASSERT(lpsz == NULL || AfxIsValidString(lpsz));<BR>&nbsp;&nbsp;&nbsp;&nbsp;CString s;<BR>&nbsp;&nbsp;&nbsp;&nbsp;s.ConcatCopy(CString::SafeStrlen(lpsz), lpsz, string.GetData()-&gt;nDataLength,<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;string.m_pchData);<BR>&nbsp;&nbsp;&nbsp;&nbsp;return s;<BR>}
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回复者：罗兹维尔 回复日期：2003-07-03 23:08:16
<br>内容：我看过CString里面的operate +<BR>不过还不懂为什么要两个参数，一个参数不也行吗<BR><BR>好像有点明白了，不知道对不对
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回复者：罗兹维尔 回复日期：2003-07-04 21:22:51
<br>内容：根据c的语法<BR><BR>int i = 1;<BR>int j = 2;<BR>i + j;<BR><BR>//i == 1;<BR><BR><BR>如果重载+后<BR>MyString str1 = "hello ";<BR>MyString str2 = "world";<BR><BR>// str1 + str2 == "hello world"<BR><BR>有伪c语法<BR>
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<font color=red>答案被接受</font><br>回复者：上海到深圳 回复日期：2003-07-05 21:23:46
<br>内容：在类中重载+则只需一个参数，如果在全局中重载+则只需两个参数
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回复者：Let's do better! 回复日期：2003-07-05 21:53:03
<br>内容：其实，两个参数的重载operator+函数是全局函数（类的友员函数），其两个参数是同一类的两个具体对象。形如add(a,b),结果在a中。<BR>而一个参数的重载operator+函数是类的成员函数，其一个参数是该类的一具体对象。形如a.add(b)),结果在a中。
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