wwwtc1.htm

来自「C++builder学习资料C++builder」· HTM 代码 · 共 83 行

HTM
83 行
字号 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<HTML><HEAD><TITLE>What's Wrong With This Code? Volume #1</TITLE>

<META content="text/html; charset=gb2312" http-equiv=Content-Type>

<META content="Harold Howe" name=Author>

<META content="MSHTML 5.00.2614.3500" name=GENERATOR></HEAD>

<BODY>

<CENTER>

<TABLE border=0 cellPadding=0 cellSpacing=0 width=640>

  <TBODY>

  <TR>

    <TD>

      <H2>What's Wrong With This Code? Volume #1 </H2>

      <H4>The assignment operator </H4>

      <P>Experienced programmers will tell you that most C++ classes should 

      contain, at a minimum, a default constructor, a copy constructor, an 

      assignment operator, and a destructor. The following code example contains 

      a class called <TT>Foo</TT> that attempts to follow these guidelines. The 

      code also contains a factory method called <TT>GetAFoo</TT>, whose sole 

      purpose is to create and return new <TT>Foo</TT> objects. </P><PRE><FONT color=green>#include &lt;iostream&gt;</FONT>



<B>using</B> <B>namespace</B> std<B>;</B>



<B>class</B> Foo

<B>{</B>

<B>public</B><B>:</B>

    Foo<B>(</B><B>)</B>

    <B>{</B>

        cout <B>&lt;&lt;</B> <FONT color=blue>"default constructor"</FONT> <B>&lt;&lt;</B> endl<B>;</B>

    <B>}</B>



    Foo<B>(</B><B>const</B> Foo <B>&amp;</B><B>)</B>

    <B>{</B>

        cout <B>&lt;&lt;</B> <FONT color=blue>"copy construction"</FONT> <B>&lt;&lt;</B> endl<B>;</B>

    <B>}</B>



    <B>~</B>Foo<B>(</B><B>)</B>

    <B>{</B>

        cout <B>&lt;&lt;</B> <FONT color=blue>"destructor"</FONT> <B>&lt;&lt;</B> endl<B>;</B>

    <B>}</B>



    Foo<B>&amp;</B> <B>operator</B><B>=</B><B>(</B>Foo <B>&amp;</B>rhs<B>)</B>

    <B>{</B>

        cout <B>&lt;&lt;</B> <FONT color=blue>"assignment"</FONT> <B>&lt;&lt;</B> endl<B>;</B>

        <B>return</B> <B>*</B><B>this</B><B>;</B>

    <B>}</B>

<B>}</B><B>;</B>





Foo GetAFoo<B>(</B><B>)</B>

<B>{</B>

    Foo foo<B>;</B>

    <B>return</B> foo<B>;</B>

<B>}</B>





<B>int</B> main<B>(</B><B>)</B>

<B>{</B>

    Foo foo1<B>;</B>

    Foo foo2<B>;</B>

    foo1 <B>=</B> GetAFoo<B>(</B><B>)</B><B>;</B>   <FONT color=navy>// generates compiler error</FONT>

    foo2 <B>=</B> foo1<B>;</B>        <FONT color=navy>// compiles OK</FONT>

    <B>return</B> <FONT color=blue>0</FONT><B>;</B>

<B>}</B>

</PRE>

      <P>Notice that the <TT>Foo</TT> class provides a default constructor, a 

      copy constructor, a destructor, and an assignment operator. Despite our 

      best intentions, the code contains a couple of problems. First and 

      foremost, it does not compile. The compiler error is: </P><PRE>[C++ Error] broken.cpp(43):

E2285 Could not find a match for 'Foo::operator =(Foo)'.

</PRE>

      <P>The <TT>Foo</TT> class clearly provides an assignment operator that 

      allows you to assign one <TT>Foo</TT> object to another. But the compiler 

      complains that it can't find an assignment operator for the assignment to 

      <TT>foo1</TT>. This seems strange, since the assignment to <TT>foo2</TT> 

      compiles fine. So what's the difference between the two? Can you find the 

      problem and fix the code so it compiles without error? </P>

      <P>In addition to fixing the compilation error, see if you can streamline 

      the code a little bit. There are at least two places where you could 

      improve the runtime performance of the program by making only minor 

      changes to the source. </P>

      <H4><A href="wwwtc1answer.htm" 

      target=_top>Answer</A> </H4></TD></TR></TBODY></TABLE></CENTER></BODY></HTML>

wwwtc1.htm - 源码说明

本页面展示了「C++builder学习资料C++builder」中的 wwwtc1.htm 源码文件，采用 HTM 编程语言编写，共 83 行代码。您可以在线阅读完整代码内容，也可以返回资源详情页下载完整源码包进行本地学习和开发。

虫虫下载站收录了大量与builder相关的技术资源，包括源代码、技术文档、电路图等，是电子工程师和嵌入式开发者的专业学习平台。

⌨️ 快捷键说明

复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?