subject_37850.htm

vc

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序号：37850 发表者：heavenkiller 发表日期：2003-04-28 22:04:22
<br>主题：教教我!!教教我!!教教我!!
<br>内容：有这样一个类的实现：<BR><BR>class NullObject:public Object<BR>{<BR>private:<BR>&nbsp;&nbsp;&nbsp;&nbsp;static NullObject instance;<BR>&nbsp;&nbsp;&nbsp;&nbsp;NullObject();<BR>protected:<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; int ...<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ....<BR>public:<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...<BR><BR>NullObject NullObject::instance; //什么意思？<BR><BR>NullObject::NullObject ()<BR>&nbsp;&nbsp;&nbsp;&nbsp;{}<BR><BR>bool NullObject::IsNull () const<BR>&nbsp;&nbsp;&nbsp;&nbsp;{ return true; }<BR><BR>int NullObject::CompareTo (Object const&amp;) const<BR>&nbsp;&nbsp;&nbsp;&nbsp;{ return 0; } <BR><BR>//HashValue NullObject::Hash () const<BR> //&nbsp;&nbsp; { return 0; }<BR><BR>void NullObject::Put (ostream&amp; s) const<BR>&nbsp;&nbsp;&nbsp;&nbsp;{ s &lt;&lt; "NullObject"; }<BR><BR>NullObject&amp; NullObject::Instance ()<BR>&nbsp;&nbsp;&nbsp;&nbsp;{ return instance; }<BR><BR>其中NullObject NullObject::instance; 这一句是什么意思？这个格式怎么这么特别，既不是初始化，也不是成员函数!哪位大虾行行好，教教我!!
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<font color=red>答案被接受</font><br>回复者：wowow 回复日期：2003-04-29 09:02:27
<br>内容：在类中，static变量要放在定义的外面进行初始化。<BR>第一个NullObject表示变量类型，这句话会调用NullObject的构造函数初始化instance。
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