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

📁 最为全面的c++内存模型探秘。不管是初学者还是老手
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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><BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestPointerAndReference2()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;TestChangeValue();<BR>&nbsp;&nbsp;&nbsp;&nbsp;TestChangePointer();<BR>}</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>运行结果如下：</P>
<P><IMG 
src="[C++对象模型][2]指针与引用 - iTech's Blog - 博客园.files/2009022020155223.png"></P>
<P>四 函数参数传递方式，函数中return语句和拷贝构造函数的关系</P>
<P>通过上面的2个实例，如果还有人对函数的参数传递方式和return有疑问的啊，可以对下面的代码亲自debug。</P>
<P>&nbsp;</P>
<DIV class=cnblogs_code><IMG id=Code_Closed_Image_201842 style="DISPLAY: none" 
onclick="this.style.display='none'; document.getElementById('Code_Closed_Text_201842').style.display='none'; document.getElementById('Code_Open_Image_201842').style.display='inline'; document.getElementById('Code_Open_Text_201842').style.display='inline';" 
height=16 src="[C++对象模型][2]指针与引用 - iTech's Blog - 博客园.files/ContractedBlock.gif" 
width=11 align=top><IMG id=Code_Open_Image_201842 
onclick="this.style.display='none'; document.getElementById('Code_Open_Text_201842').style.display='none'; getElementById('Code_Closed_Image_201842').style.display='inline'; getElementById('Code_Closed_Text_201842').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_201842>Code</SPAN><SPAN id=Code_Open_Text_201842><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;CopyAndAssign<BR>{<BR></SPAN><SPAN 
style="COLOR: #0000ff">public</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssign(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;i)<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;i;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssign(</SPAN><SPAN 
style="COLOR: #0000ff">const</SPAN><SPAN 
style="COLOR: #000000">&nbsp;CopyAndAssign</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ca)<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">拷贝构造！</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;&nbsp;&nbsp;&nbsp;&nbsp;x&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ca.x;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssign</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">operator</SPAN><SPAN style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">(</SPAN><SPAN style="COLOR: #0000ff">const</SPAN><SPAN 
style="COLOR: #000000">&nbsp;CopyAndAssign</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ca)<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">赋值操作符</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;&nbsp;&nbsp;&nbsp;&nbsp;x&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ca.x;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #0000ff">this</SPAN><SPAN 
style="COLOR: #000000">;<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>};<BR><BR>CopyAndAssign&nbsp;ReturnCopyAndAssign()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssign&nbsp;temp(</SPAN><SPAN 
style="COLOR: #800080">20</SPAN><SPAN 
style="COLOR: #000000">);&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;构造</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;temp;<BR>}<BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;CopyAndAssignAsParameter(CopyAndAssign&nbsp;ca)<BR>{<BR>}<BR><BR>CopyAndAssign</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ReturnCopyAndAssignByReference()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssign&nbsp;temp(</SPAN><SPAN 
style="COLOR: #800080">20</SPAN><SPAN 
style="COLOR: #000000">);&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;构造</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;temp;<BR>}<BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;CopyAndAssignAsParameterByReference(CopyAndAssign</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ca)<BR>{<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestCopyAndAssign()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssign&nbsp;c1(</SPAN><SPAN 
style="COLOR: #800080">10</SPAN><SPAN 
style="COLOR: #000000">);&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;构造</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssignAsParameter(c1);&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;拷贝构造</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;ReturnCopyAndAssign();&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;拷贝构造</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000"><BR>&nbsp;&nbsp;&nbsp;&nbsp;CopyAndAssignAsParameterByReference(c1);&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;ReturnCopyAndAssignByReference();&nbsp;<BR>}</SPAN></SPAN></DIV>
<P>亲自debug，效果会更好，运行结果如下：</P>
<P>&nbsp;</P>
<P><IMG 
src="[C++对象模型][2]指针与引用 - iTech's Blog - 博客园.files/2009022020204333.png"></P>
<P>五 总结</P>
<P><SPAN style="COLOR: #ff0000">1) 指针也是变量，它存储其他变量的地址。例如int *p = new int(10); 
p是指针变量，p实际是存储了一个int变量的地址。<BR>2）引用其实是一个别名，跟原对象是同一个东东。例如 std::string str = 
"hello"; std::string &amp; strR = 
str;此时strR跟str其实是同一个东东，strR可以看成是str的一个小名。<BR>3）函数默认的传参方式为按值传递，即当实参传入是其实是做了拷贝,函数内其实是对所拷贝对象的操作。例如 
void Increase(int x) { x++; } 调用时 int i = 10; Increase(i); 
Increase函数内部其实是对i的一个拷贝（我们假设为ii）进行++。所以在函数调用结束后原来的i的值仍然保持不变。<BR>4）函数的传参方式可以显示的指定按引用来传递，按引用传递时，函数内即对实参的操作，没有拷贝操作，所以函数内对实参的修改，当然后调用结束后反映到实参上。例如void 
Increase(int &amp; x) { x++;} 调用 int i = 10; 
Increase(i);此时Increase内部的++即是对i的操作，所以函数调用结束后i的值被修改。<BR>5）函数中如果有return返回变量时，其实所返回的也是一个拷贝。所以当使用return返回对象时一定要考虑所返回对象的拷贝构造函数是否能够满足要求。</SPAN></P>
<P>六 使用注意</P>
<P><SPAN style="COLOR: #ff0000">1) malloc/free一起使用。</SPAN></P>
<P><SPAN style="COLOR: #ff0000">2）new/delete一起使用。</SPAN></P>
<P><SPAN style="COLOR: #ff0000">3）对于new中有[]时，相应的必须使用delete[]来释放。</SPAN></P>
<P><SPAN 
style="COLOR: #ff0000">4）用free或delete释放了内存之后，立即将指针设置为NULL，防止产生“野指针”。</SPAN></P>
<P><SPAN style="COLOR: #ff0000">5）对指针的使用前，应该检查是否为空，空指针可能导致程序崩溃。</SPAN></P>
<P><SPAN style="COLOR: #ff0000">6）非内置类型的参数传递，使用const引用代替一般变量。</SPAN></P>
<P>七 谢谢！<B><BR></B></P>
<P><B><BR></B></P>
<DIV id=MySignature>
<P>感谢，Thanks！<BR><BR>作者：<A href="http://itech.cnblogs.com/">iTech</A><BR>出处：<A 
href="http://itech.cnblogs.com/">http://itech.cnblogs.com/</A> 
<BR>转载：本文版权归作者iTech所有，转载请注明出处，不得用于商业用途！</P></DIV>
<DIV id=EntryTag>Tag标签: <A 
href="http://www.cnblogs.com/itech/tag/[Cpp对象模型]/">[Cpp对象模型]</A></DIV></DIV>
<DIV class=postDesc>posted @ 2009-02-20 09:11 <A 
href="http://www.cnblogs.com/itech/">iTech</A> 阅读(118) <A 
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