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diff --git a/share/doc/stabs/Virtual-Base-Classes.html b/share/doc/stabs/Virtual-Base-Classes.html new file mode 100644 index 0000000..5244ad4 --- /dev/null +++ b/share/doc/stabs/Virtual-Base-Classes.html @@ -0,0 +1,125 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1992-2023 Free Software Foundation, Inc. +Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon, +and David MacKenzie. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +Texts. A copy of the license is included in the section entitled "GNU +Free Documentation License". --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>STABS: Virtual Base Classes</title> + +<meta name="description" content="STABS: Virtual Base Classes"> +<meta name="keywords" content="STABS: Virtual Base Classes"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Cplusplus.html#Cplusplus" rel="up" title="Cplusplus"> +<link href="Static-Members.html#Static-Members" rel="next" title="Static Members"> +<link href="Inheritance.html#Inheritance" rel="previous" title="Inheritance"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Virtual-Base-Classes"></a> +<div class="header"> +<p> +Next: <a href="Static-Members.html#Static-Members" accesskey="n" rel="next">Static Members</a>, Previous: <a href="Inheritance.html#Inheritance" accesskey="p" rel="previous">Inheritance</a>, Up: <a href="Cplusplus.html#Cplusplus" accesskey="u" rel="up">Cplusplus</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Virtual-Base-Classes-1"></a> +<h3 class="section">8.13 Virtual Base Classes</h3> + +<p>A derived class object consists of a concatenation in memory of the data +areas defined by each base class, starting with the leftmost and ending +with the rightmost in the list of base classes. The exception to this +rule is for virtual inheritance. In the example above, class <code>D</code> +inherits virtually from base class <code>B</code>. This means that an +instance of a <code>D</code> object will not contain its own <code>B</code> part but +merely a pointer to a <code>B</code> part, known as a virtual base pointer. +</p> +<p>In a derived class stab, the base offset part of the derivation +information, described above, shows how the base class parts are +ordered. The base offset for a virtual base class is always given as 0. +Notice that the base offset for <code>B</code> is given as 0 even though +<code>B</code> is not the first base class. The first base class <code>A</code> +starts at offset 0. +</p> +<p>The field information part of the stab for class <code>D</code> describes the field +which is the pointer to the virtual base class <code>B</code>. The vbase pointer +name is ‘<samp>$vb</samp>’ followed by a type reference to the virtual base class. +Since the type id for <code>B</code> in this example is 25, the vbase pointer name +is ‘<samp>$vb25</samp>’. +</p> +<div class="smallexample"> +<pre class="smallexample">.stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:1, + 160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i; + 2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;28;;D_virt: + :32:i;2A*-2147483646;31;;;~%20;",128,0,0,0 +</pre></div> + +<p>Following the name and a semicolon is a type reference describing the +type of the virtual base class pointer, in this case 24. Type 24 was +defined earlier as the type of the <code>B</code> class <code>this</code> pointer. The +<code>this</code> pointer for a class is a pointer to the class type. +</p> +<div class="example"> +<pre class="example">.stabs "this:P24=*25=xsB:",64,0,0,8 +</pre></div> + +<p>Finally the field offset part of the vbase pointer field description +shows that the vbase pointer is the first field in the <code>D</code> object, +before any data fields defined by the class. The layout of a <code>D</code> +class object is a follows, <code>Adat</code> at 0, the vtable pointer for +<code>A</code> at 32, <code>Cdat</code> at 64, the vtable pointer for C at 96, the +virtual base pointer for <code>B</code> at 128, and <code>Ddat</code> at 160. +</p> + +<hr> +<div class="header"> +<p> +Next: <a href="Static-Members.html#Static-Members" accesskey="n" rel="next">Static Members</a>, Previous: <a href="Inheritance.html#Inheritance" accesskey="p" rel="previous">Inheritance</a>, Up: <a href="Cplusplus.html#Cplusplus" accesskey="u" rel="up">Cplusplus</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |