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<TD align=left width=300><B>关键字:</B><BR>Effective C++ </TD>
<TD align=middle width=120><B>贴文时间</B><BR>2001-7-2 21:01:37 </TD>
<TD align=middle width=80><B>文章类型: </B><BR>翻译 </TD>
<TD align=middle width=100><B>给贴子投票 </B><BR><A
href="http://www.csdn.net/develop/addscore.asp?id=8614">投票</A> </TD></TR>
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<TD> lostmouse 翻译 </TD>
<TD vAlign=top colSpan=3><B>出处: </B><A
href="http://www.csdn.net/develop/article/8/Effective%20C++%202e%20electronic%20book">Effective
C++ 2e electronic book </A></TD></TR>
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<P>条款8. 写operator new和operator delete时要遵循常规</P>
<P>自己重写operator new时(条款10解释了为什么有时要重写它)，很重要的一点是函数提供的行为要和系统缺省的operator
new一致。实际做起来也就是：要有正确的返回值；可用内存不够时要调用出错处理函数(见条款7)；处理好0字节内存请求的情况。此外，还要避免不小心隐藏了标准形式的new，不过这是条款9的话题。</P>
<P>有关返回值的部分很简单。如果内存分配请求成功，就返回指向内存的指针；如果失败，则遵循条款7的规定抛出一个std::bad_alloc类型的异常。</P>
<P>但事情也不是那么简单。因为operator
new实际上会不只一次地尝试着去分配内存，它要在每次失败后调用出错处理函数，还期望出错处理函数能想办法释放别处的内存。只有在指向出错处理函数的指针为空的情况下，operator
new才抛出异常。</P>
<P>另外，C++标准要求，即使在请求分配0字节内存时，operator
new也要返回一个合法指针。(实际上，这个听起来怪怪的要求确实给C++语言其它地方带来了简便)</P>
<P>这样，非类成员形式的operator new的伪代码看起来会象下面这样：<BR>void * operator new(size_t
size) // operator
new还可能有其它参数<BR>{
</P>
<P> if (size == 0)
{
// 处理0字节请求时，<BR> size =
1;
// 把它当作1个字节请求来处理<BR>
}
<BR> while (1) {<BR> 分配size字节内存;</P>
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