📄 copy-assignment.html

📁 自己收集的linux入门到学懂高级编程书集包括linux程序设计第三版
💻 HTML
字号:
<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright &copy; 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.   <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below).  A copy of the license isincluded in the section entitled "GNU Free Documentation License".   <p>(a) The FSF's Front-Cover Text is:   <p>A GNU Manual   <p>(b) The FSF's Back-Cover Text is:   <p>You have freedom to copy and modify this GNU Manual, like GNU     software.  Copies published by the Free Software Foundation raise     funds for GNU development.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!--  pre.display { font-family:inherit }  pre.format  { font-family:inherit }  pre.smalldisplay { font-family:inherit; font-size:smaller }  pre.smallformat  { font-family:inherit; font-size:smaller }  pre.smallexample { font-size:smaller }  pre.smalllisp    { font-size:smaller }--></style></head><body><div class="node"><p>Node:&nbsp;<a name="Copy%20Assignment">Copy Assignment</a>,Previous:&nbsp;<a rel="previous" accesskey="p" href="Temporaries.html#Temporaries">Temporaries</a>,Up:&nbsp;<a rel="up" accesskey="u" href="C---Misunderstandings.html#C++%20Misunderstandings">C++ Misunderstandings</a><hr><br></div><h3 class="subsection">Implicit Copy-Assignment for Virtual Bases</h4><p>When a base class is virtual, only one subobject of the base classbelongs to each full object.  Also, the constructors and destructors areinvoked only once, and called from the most-derived class.  However, suchobjects behave unspecified when being assigned.  For example:<pre class="smallexample">     struct Base{       char *name;       Base(char *n) : name(strdup(n)){}       Base&amp; operator= (const Base&amp; other){        free (name);        name = strdup (other.name);       }     };          struct A:virtual Base{       int val;       A():Base("A"){}     };          struct B:virtual Base{       int bval;       B():Base("B"){}     };          struct Derived:public A, public B{       Derived():Base("Derived"){}     };          void func(Derived &amp;d1, Derived &amp;d2)     {       d1 = d2;     }     </pre>   <p>The C++ standard specifies that <code>Base::Base</code> is only called oncewhen constructing or copy-constructing a Derived object.  It isunspecified whether <code>Base::operator=</code> is called more than once whenthe implicit copy-assignment for Derived objects is invoked (as it isinside <code>func</code> in the example).   <p>G++ implements the "intuitive" algorithm for copy-assignment: assign alldirect bases, then assign all members.  In that algorithm, the virtualbase subobject can be encountered more than once.  In the example, copyingproceeds in the following order: <code>val</code>, <code>name</code> (via<code>strdup</code>), <code>bval</code>, and <code>name</code> again.   <p>If application code relies on copy-assignment, a user-definedcopy-assignment operator removes any uncertainties.  With such anoperator, the application can define whether and how the virtual basesubobject is assigned.   </body></html>
⌨️ 快捷键说明

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