📄 [c++对象模型][2]指针与引用 - itech's blog - 博客园.htm

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style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;请问运行Test6函数会有什么样的结果？<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000"><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;答：篡改动态内存区的内容，后果难以预料，非常危险。<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000"><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;因为free(str);之后，str成为野指针，<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;if(str&nbsp;!=&nbsp;NULL)语句不起作用。<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//<BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Test6();<BR><BR>}&nbsp;</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>三 C++指针与引用</P>
<P>引用，其实是变量的别名，与变量是同一个东东。例如 int i = 10; int &amp;a = i; int &amp;b = i; 这样 
a，b为i的引用，即a，b为i的别名，还有 int * pi = new int(10); int *&amp; pa = pi; int *&amp; pb 
= pi; 
此时pa，pb为pi的别名。在C++中引入了引用概念后，我们不仅可以定义引用变量，相应的函数的传递方式也增加了按引用传递，当参数以引用方式传递时，函数调用时不对实参进行拷贝，传入函数内的变量与实参是同一个变量。下面的实例演示了指针和引用在C++的使用。</P>
<P>&nbsp;</P>
<DIV class=cnblogs_code><IMG id=Code_Closed_Image_230154 style="DISPLAY: none" 
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width=11 align=top><IMG id=Code_Open_Image_230154 
onclick="this.style.display='none'; document.getElementById('Code_Open_Text_230154').style.display='none'; getElementById('Code_Closed_Image_230154').style.display='inline'; getElementById('Code_Closed_Text_230154').style.display='inline';" 
height=16 
src="[C++对象模型][2]指针与引用 - iTech's Blog - 博客园.files/ExpandedBlockStart.gif" 
width=11 align=top><SPAN class=cnblogs_code_Collapse 
id=Code_Closed_Text_230154>Code</SPAN><SPAN id=Code_Open_Text_230154><BR><!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--><SPAN 
style="COLOR: #0000ff">#pragma</SPAN><SPAN 
style="COLOR: #000000">&nbsp;once</SPAN><SPAN 
style="COLOR: #000000"><BR>#include&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN 
style="COLOR: #000000">iostream</SPAN><SPAN 
style="COLOR: #000000">&gt;</SPAN><SPAN 
style="COLOR: #000000"><BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">class</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Point<BR>{<BR></SPAN><SPAN 
style="COLOR: #0000ff">public</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;Point(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_x&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_y&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;SetX(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_x&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;SetY(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_y&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;PrintPoint()<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;std::cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">The&nbsp;Point&nbsp;is&nbsp;:&nbsp;</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">'</SPAN><SPAN 
style="COLOR: #800000">(</SPAN><SPAN style="COLOR: #800000">'</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;_x&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">'</SPAN><SPAN 
style="COLOR: #800000">,</SPAN><SPAN style="COLOR: #800000">'</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;_y&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">'</SPAN><SPAN 
style="COLOR: #800000">)</SPAN><SPAN style="COLOR: #800000">'</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;std::endl;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;PrintPointAdress()<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;std::cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">The&nbsp;Point's&nbsp;adress&nbsp;is&nbsp;:&nbsp;</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">this</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;std::endl;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR></SPAN><SPAN 
style="COLOR: #0000ff">private</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;_x;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;_y;<BR>};<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;默认按值传递，当传入时对对像进行了拷贝，函数内只是对所拷贝值的修改，所以实参没被修改。</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ChangeValue(Point&nbsp;pt,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.SetX(x);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.SetY(y);<BR>}<BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;按引用传递，函数内外同一值，所以修改了实参。</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ChangeValueByReference(Point</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pt,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.SetX(x);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.SetY(y);<BR>}<BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;通过传递指针，虽然实参指针传入时也产生了拷贝，但是在函数内通过指针任然修改了指针所指的值。</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ChangeValueByPointer(Point&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pt,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">SetX(x);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">SetY(y);<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestChangeValue()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;Point&nbsp;pt(</SPAN><SPAN 
style="COLOR: #800080">10</SPAN><SPAN style="COLOR: #000000">,</SPAN><SPAN 
style="COLOR: #800080">10</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.PrintPoint();<BR>&nbsp;&nbsp;&nbsp;&nbsp;ChangeValue(pt,</SPAN><SPAN 
style="COLOR: #800080">100</SPAN><SPAN style="COLOR: #000000">,</SPAN><SPAN 
style="COLOR: #800080">100</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.PrintPoint();<BR>&nbsp;&nbsp;&nbsp;&nbsp;ChangeValueByReference(pt,</SPAN><SPAN 
style="COLOR: #800080">200</SPAN><SPAN style="COLOR: #000000">,</SPAN><SPAN 
style="COLOR: #800080">200</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.PrintPoint();<BR>&nbsp;&nbsp;&nbsp;&nbsp;ChangeValueByPointer(</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN style="COLOR: #000000">pt,</SPAN><SPAN 
style="COLOR: #800080">300</SPAN><SPAN style="COLOR: #000000">,</SPAN><SPAN 
style="COLOR: #800080">300</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pt.PrintPoint();<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;按引用传递，所以指针可以被返回。</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ChangePointerByReference(Point&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pPt,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;pPt&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Point(x,&nbsp;y);<BR>}<BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;对二级指针拷贝，但是二级指针指向的一级指针被返回。</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ChangePointerByTwoLevelPointer(Point&nbsp;</SPAN><SPAN 
style="COLOR: #000000">**</SPAN><SPAN 
style="COLOR: #000000">pPt,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pPt&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Point(x,&nbsp;y);<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestChangePointer()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;Point&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pPt&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL;<BR>&nbsp;&nbsp;&nbsp;&nbsp;ChangePointerByReference(pPt,&nbsp;</SPAN><SPAN 
style="COLOR: #800080">1000</SPAN><SPAN style="COLOR: #000000">,</SPAN><SPAN 
style="COLOR: #800080">1000</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pPt</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">PrintPoint();<BR>&nbsp;&nbsp;&nbsp;&nbsp;pPt</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">PrintPointAdress();<BR>&nbsp;&nbsp;&nbsp;&nbsp;delete&nbsp;pPt;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pPt&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">p&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">(</SPAN><SPAN 
style="COLOR: #800080">10</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">int&nbsp;*p2&nbsp;=&nbsp;new&nbsp;int(10);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">int&nbsp;*p3&nbsp;=&nbsp;new&nbsp;int(10);</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000"><BR>&nbsp;&nbsp;&nbsp;&nbsp;ChangePointerByTwoLevelPointer(</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">pPt,&nbsp;</SPAN><SPAN 
style="COLOR: #800080">2000</SPAN><SPAN style="COLOR: #000000">,</SPAN><SPAN 
style="COLOR: #800080">2000</SPAN><SPAN
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