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diff --git a/share/doc/gcc/Local-Labels.html b/share/doc/gcc/Local-Labels.html new file mode 100644 index 0000000..9dacfc3 --- /dev/null +++ b/share/doc/gcc/Local-Labels.html @@ -0,0 +1,164 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +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 the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +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. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Local Labels</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Local Labels"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Local Labels"> +<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="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions"> +<link href="Labels-as-Values.html#Labels-as-Values" rel="next" title="Labels as Values"> +<link href="Statement-Exprs.html#Statement-Exprs" rel="previous" title="Statement Exprs"> +<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_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Local-Labels"></a> +<div class="header"> +<p> +Next: <a href="Labels-as-Values.html#Labels-as-Values" accesskey="n" rel="next">Labels as Values</a>, Previous: <a href="Statement-Exprs.html#Statement-Exprs" accesskey="p" rel="previous">Statement Exprs</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Locally-Declared-Labels"></a> +<h3 class="section">6.2 Locally Declared Labels</h3> +<a name="index-local-labels"></a> +<a name="index-macros_002c-local-labels"></a> + +<p>GCC allows you to declare <em>local labels</em> in any nested block +scope. A local label is just like an ordinary label, but you can +only reference it (with a <code>goto</code> statement, or by taking its +address) within the block in which it is declared. +</p> +<p>A local label declaration looks like this: +</p> +<div class="smallexample"> +<pre class="smallexample">__label__ <var>label</var>; +</pre></div> + +<p>or +</p> +<div class="smallexample"> +<pre class="smallexample">__label__ <var>label1</var>, <var>label2</var>, /* <span class="roman">…</span> */; +</pre></div> + +<p>Local label declarations must come at the beginning of the block, +before any ordinary declarations or statements. +</p> +<p>The label declaration defines the label <em>name</em>, but does not define +the label itself. You must do this in the usual way, with +<code><var>label</var>:</code>, within the statements of the statement expression. +</p> +<p>The local label feature is useful for complex macros. If a macro +contains nested loops, a <code>goto</code> can be useful for breaking out of +them. However, an ordinary label whose scope is the whole function +cannot be used: if the macro can be expanded several times in one +function, the label is multiply defined in that function. A +local label avoids this problem. For example: +</p> +<div class="smallexample"> +<pre class="smallexample">#define SEARCH(value, array, target) \ +do { \ + __label__ found; \ + typeof (target) _SEARCH_target = (target); \ + typeof (*(array)) *_SEARCH_array = (array); \ + int i, j; \ + int value; \ + for (i = 0; i < max; i++) \ + for (j = 0; j < max; j++) \ + if (_SEARCH_array[i][j] == _SEARCH_target) \ + { (value) = i; goto found; } \ + (value) = -1; \ + found:; \ +} while (0) +</pre></div> + +<p>This could also be written using a statement expression: +</p> +<div class="smallexample"> +<pre class="smallexample">#define SEARCH(array, target) \ +({ \ + __label__ found; \ + typeof (target) _SEARCH_target = (target); \ + typeof (*(array)) *_SEARCH_array = (array); \ + int i, j; \ + int value; \ + for (i = 0; i < max; i++) \ + for (j = 0; j < max; j++) \ + if (_SEARCH_array[i][j] == _SEARCH_target) \ + { value = i; goto found; } \ + value = -1; \ + found: \ + value; \ +}) +</pre></div> + +<p>Local label declarations also make the labels they declare visible to +nested functions, if there are any. See <a href="Nested-Functions.html#Nested-Functions">Nested Functions</a>, for details. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Labels-as-Values.html#Labels-as-Values" accesskey="n" rel="next">Labels as Values</a>, Previous: <a href="Statement-Exprs.html#Statement-Exprs" accesskey="p" rel="previous">Statement Exprs</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |