subject_38895.htm

一些关于vc的问答

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序号：38895 发表者：IEEE 发表日期：2003-05-06 21:08:44
<br>主题：C++问题
<br>内容：#include "iostream.h"<BR>#include "string.h"<BR>class A<BR>{<BR>public:<BR>&nbsp;&nbsp;&nbsp;&nbsp;virtual&nbsp;&nbsp;&nbsp;&nbsp; ~A() {cout&lt;&lt;"A::~A() called!\n";}<BR>};<BR><BR>class B:public A<BR>{<BR>public:<BR>&nbsp;&nbsp;&nbsp;&nbsp;B(int i) {buf=new char[i];}<BR>&nbsp;&nbsp;&nbsp;&nbsp;~B() {delete []buf; cout&lt;&lt;"B::~B() called!\n";}<BR>private:<BR>&nbsp;&nbsp;&nbsp;&nbsp;char *buf;<BR>};<BR><BR>void fun (A *a) { delete a; }<BR><BR>void main()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;A *a=new B(15);<BR>&nbsp;&nbsp;&nbsp;&nbsp;//B b(19);<BR>&nbsp;&nbsp;&nbsp;&nbsp;//a=&amp;b;<BR>&nbsp;&nbsp;&nbsp;&nbsp;fun(a);<BR>}<BR>该程序运行时，析构函数的调用实现了多态性，编译通过，运行正常。<BR>但是将其中的两条注释掉的语句加入main()之后，编译通过，但运行时出了问题！<BR>&nbsp;&nbsp;&nbsp;&nbsp;请指点。
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回复者：Justin Le 回复日期：2003-05-06 21:53:53
<br>内容：//可以运行，没明白你的意思<BR>#include "iostream.h"<BR>#include "string.h"<BR>#include &lt;stdio.h&gt;<BR>class A<BR>{<BR>public:<BR>&nbsp;&nbsp;&nbsp;&nbsp;virtual&nbsp;&nbsp;&nbsp;&nbsp; ~A() {cout&lt;&lt;"A::~A() called!\n";}<BR>};<BR><BR>class B:public A<BR>{<BR>public:<BR>&nbsp;&nbsp;&nbsp;&nbsp;B(int i) {printf("in B %d\n",i);buf=new char[i];}<BR>&nbsp;&nbsp;&nbsp;&nbsp;~B() {delete []buf; cout&lt;&lt;"B::~B() called!\n";}<BR>private:<BR>&nbsp;&nbsp;&nbsp;&nbsp;char *buf;<BR>};<BR><BR>void fun (A *a) { delete a; }<BR><BR>void main()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;A *a=new B(15);<BR>&nbsp;&nbsp;&nbsp;&nbsp;B b(19);<BR>&nbsp;&nbsp;&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;a=&amp;b;<BR>&nbsp;&nbsp;&nbsp;&nbsp;fun(a);<BR>}<BR>
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<font color=red>答案被接受</font><br>回复者：ArthurTu 回复日期：2003-05-06 23:04:05
<br>内容：A *a=new B(15);<BR>&nbsp;&nbsp;&nbsp;&nbsp;B b(19);<BR>&nbsp;&nbsp;&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;a=&amp;b;<BR>fun(a);<BR>pointer a开始指向new出来的一个B的实例，然后有把他指向另外一个B的实例（还不是new出来的）！然后又在fun里面delete不是new出来的这个实例！<BR>不错才怪！
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回复者：IEEE 回复日期：2003-05-10 10:00:13
<br>内容：我已经找到答案了，谢谢大家！
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