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A copy of the license is included in the section entitled "GNU 12Free Documentation License". --> 13<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 14<head> 15<title>STABS: Unions</title> 16 17<meta name="description" content="STABS: Unions"> 18<meta name="keywords" content="STABS: Unions"> 19<meta name="resource-type" content="document"> 20<meta name="distribution" content="global"> 21<meta name="Generator" content="makeinfo"> 22<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 23<link href="index.html#Top" rel="start" title="Top"> 24<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index"> 25<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 26<link href="Types.html#Types" rel="up" title="Types"> 27<link href="Function-Types.html#Function-Types" rel="next" title="Function Types"> 28<link href="Typedefs.html#Typedefs" rel="previous" title="Typedefs"> 29<style type="text/css"> 30<!-- 31a.summary-letter {text-decoration: none} 32blockquote.smallquotation {font-size: smaller} 33div.display {margin-left: 3.2em} 34div.example {margin-left: 3.2em} 35div.indentedblock {margin-left: 3.2em} 36div.lisp {margin-left: 3.2em} 37div.smalldisplay {margin-left: 3.2em} 38div.smallexample {margin-left: 3.2em} 39div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 40div.smalllisp {margin-left: 3.2em} 41kbd {font-style:oblique} 42pre.display {font-family: inherit} 43pre.format {font-family: inherit} 44pre.menu-comment {font-family: serif} 45pre.menu-preformatted {font-family: serif} 46pre.smalldisplay {font-family: inherit; font-size: smaller} 47pre.smallexample {font-size: smaller} 48pre.smallformat {font-family: inherit; font-size: smaller} 49pre.smalllisp {font-size: smaller} 50span.nocodebreak {white-space:nowrap} 51span.nolinebreak {white-space:nowrap} 52span.roman {font-family:serif; font-weight:normal} 53span.sansserif {font-family:sans-serif; font-weight:normal} 54ul.no-bullet {list-style: none} 55--> 56</style> 57 58 59</head> 60 61<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 62<a name="Unions"></a> 63<div class="header"> 64<p> 65Next: <a href="Function-Types.html#Function-Types" accesskey="n" rel="next">Function Types</a>, Previous: <a href="Typedefs.html#Typedefs" accesskey="p" rel="previous">Typedefs</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</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> 66</div> 67<hr> 68<a name="Unions-1"></a> 69<h3 class="section">5.10 Unions</h3> 70 71<div class="example"> 72<pre class="example">union u_tag { 73 int u_int; 74 float u_float; 75 char* u_char; 76} an_u; 77</pre></div> 78 79<p>This code generates a stab for a union tag and a stab for a union 80variable. Both use the <code>N_LSYM</code> stab type. If a union variable is 81scoped locally to the procedure in which it is defined, its stab is 82located immediately preceding the <code>N_LBRAC</code> for the procedure’s block 83start. 84</p> 85<p>The stab for the union tag, however, is located preceding the code for 86the procedure in which it is defined. The stab type is <code>N_LSYM</code>. This 87would seem to imply that the union type is file scope, like the struct 88type <code>s_tag</code>. This is not true. The contents and position of the stab 89for <code>u_type</code> do not convey any information about its procedure local 90scope. 91</p> 92<div class="smallexample"> 93<pre class="smallexample"># <span class="roman">128 is N_LSYM</span> 94.stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;", 95 128,0,0,0 96</pre></div> 97 98<p>The symbol descriptor ‘<samp>T</samp>’, following the ‘<samp>name:</samp>’ means that 99the stab describes an enumeration, structure, or union tag. The type 100descriptor ‘<samp>u</samp>’, following the ‘<samp>23=</samp>’ of the type definition, 101narrows it down to a union type definition. Following the ‘<samp>u</samp>’ is 102the number of bytes in the union. After that is a list of union element 103descriptions. Their format is ‘<samp><var>name</var>:<var>type</var>, <var>bit 104offset into the union</var>, <var>number of bytes for the element</var>;</samp>’. 105</p> 106<p>The stab for the union variable is: 107</p> 108<div class="example"> 109<pre class="example">.stabs "an_u:23",128,0,0,-20 # <span class="roman">128 is N_LSYM</span> 110</pre></div> 111 112<p>‘<samp>-20</samp>’ specifies where the variable is stored (see <a href="Stack-Variables.html#Stack-Variables">Stack Variables</a>). 113</p> 114 115 116 117</body> 118</html> 119