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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: #008000">&nbsp;-----------------------------------------------</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory2(</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">**</SPAN><SPAN 
style="COLOR: #000000">p,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;num)<BR>{<BR>&nbsp;&nbsp;&nbsp;&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">char</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">)malloc(num);<BR>}<BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Test2(</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL;<BR>&nbsp;&nbsp;&nbsp;&nbsp;GetMemory2(</SPAN><SPAN 
style="COLOR: #000000">&amp;</SPAN><SPAN 
style="COLOR: #000000">str,&nbsp;</SPAN><SPAN 
style="COLOR: #800080">100</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;strcpy(str,&nbsp;</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">hello&nbsp;world</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;printf(str);<BR>&nbsp;&nbsp;&nbsp;&nbsp;free(str);<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory3(</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">&nbsp;p[]&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">hello&nbsp;world</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;p;<BR>}<BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Test3(</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL;<BR>&nbsp;&nbsp;&nbsp;&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory3();<BR>&nbsp;&nbsp;&nbsp;&nbsp;printf(str);<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory4(</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</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: #800000">"</SPAN><SPAN 
style="COLOR: #800000">hello&nbsp;world</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;p;<BR>}<BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Test4()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL;<BR>&nbsp;&nbsp;&nbsp;&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory4();<BR>&nbsp;&nbsp;&nbsp;&nbsp;printf(str);<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory5(</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</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">char</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">)malloc(</SPAN><SPAN 
style="COLOR: #800080">100</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;strcpy(p,</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">hello&nbsp;world</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;p;<BR>}<BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Test5()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL;<BR>&nbsp;&nbsp;&nbsp;&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GetMemory5();<BR>&nbsp;&nbsp;&nbsp;&nbsp;printf(str);<BR>&nbsp;&nbsp;&nbsp;&nbsp;free(str);<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;Test6(&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">char</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">)malloc(</SPAN><SPAN 
style="COLOR: #800080">100</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;strcpy(str,&nbsp;</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN style="COLOR: #800000">hello</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;free(str);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">if</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(str&nbsp;</SPAN><SPAN 
style="COLOR: #000000">!=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;NULL)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;strcpy(str,&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN style="COLOR: #800000">world</SPAN><SPAN 
style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">&nbsp;);<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf(str);<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestPointerAndReference()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;请问运行Test1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：程序崩溃。同时有内存泄漏。<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;因为在GetMemory1函数的调用过程中，其实是对实参指针p做了拷贝，拷贝为局部变量，<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;在函数内的操作是对局部变量的操作，局部变量与实参是两个不同的变量，相互不影响。<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;所以，当GetMemory1调用结束时，Test1函数中的&nbsp;str一直都是&nbsp;NULL。<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;strcpy(str,&nbsp;"hello&nbsp;world");将使程序崩溃。<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">Test1();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;请问运行Test2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：(1)能够输出hello&nbsp;world;&nbsp;(2)但是调用结束要对内存释放，否则内存泄漏;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//<BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Test2();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;请问运行Test3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：可能是乱码。<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GetMemory3返回的是指向“栈内存”的指针，<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;该指针的地址不是&nbsp;NULL，但其原现的内容已经被清除，新内容不可知。<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN style="COLOR: #008000">&nbsp;</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Test3();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;请问运行Test4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：(1)能够输出hello&nbsp;world; (2) 
此时的str指向了常量区，不需要程序员释放，程序结束自动释放。<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//<BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Test4();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;请问运行Test5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：(1)能够输出hello&nbsp;world;&nbsp;(2)但是调用结束要对内存释放，否则内存泄漏;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//<BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Test5();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;-----------------------------------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN
12345

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