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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gcc/Nested-Functions.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gcc/Nested-Functions.html b/share/doc/gcc/Nested-Functions.html new file mode 100644 index 0000000..e416d13 --- /dev/null +++ b/share/doc/gcc/Nested-Functions.html @@ -0,0 +1,215 @@ +<!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): Nested Functions</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Nested Functions"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Nested Functions"> +<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="Nonlocal-Gotos.html#Nonlocal-Gotos" rel="next" title="Nonlocal Gotos"> +<link href="Labels-as-Values.html#Labels-as-Values" rel="previous" title="Labels as Values"> +<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="Nested-Functions"></a> +<div class="header"> +<p> +Next: <a href="Nonlocal-Gotos.html#Nonlocal-Gotos" accesskey="n" rel="next">Nonlocal Gotos</a>, Previous: <a href="Labels-as-Values.html#Labels-as-Values" accesskey="p" rel="previous">Labels as Values</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="Nested-Functions-1"></a> +<h3 class="section">6.4 Nested Functions</h3> +<a name="index-nested-functions"></a> +<a name="index-downward-funargs"></a> +<a name="index-thunks"></a> + +<p>A <em>nested function</em> is a function defined inside another function. +Nested functions are supported as an extension in GNU C, but are not +supported by GNU C++. +</p> +<p>The nested function’s name is local to the block where it is defined. +For example, here we define a nested function named <code>square</code>, and +call it twice: +</p> +<div class="smallexample"> +<pre class="smallexample">foo (double a, double b) +{ + double square (double z) { return z * z; } + + return square (a) + square (b); +} +</pre></div> + +<p>The nested function can access all the variables of the containing +function that are visible at the point of its definition. This is +called <em>lexical scoping</em>. For example, here we show a nested +function which uses an inherited variable named <code>offset</code>: +</p> +<div class="smallexample"> +<pre class="smallexample">bar (int *array, int offset, int size) +{ + int access (int *array, int index) + { return array[index + offset]; } + int i; + /* <span class="roman">…</span> */ + for (i = 0; i < size; i++) + /* <span class="roman">…</span> */ access (array, i) /* <span class="roman">…</span> */ +} +</pre></div> + +<p>Nested function definitions are permitted within functions in the places +where variable definitions are allowed; that is, in any block, mixed +with the other declarations and statements in the block. +</p> +<p>It is possible to call the nested function from outside the scope of its +name by storing its address or passing the address to another function: +</p> +<div class="smallexample"> +<pre class="smallexample">hack (int *array, int size) +{ + void store (int index, int value) + { array[index] = value; } + + intermediate (store, size); +} +</pre></div> + +<p>Here, the function <code>intermediate</code> receives the address of +<code>store</code> as an argument. If <code>intermediate</code> calls <code>store</code>, +the arguments given to <code>store</code> are used to store into <code>array</code>. +But this technique works only so long as the containing function +(<code>hack</code>, in this example) does not exit. +</p> +<p>If you try to call the nested function through its address after the +containing function exits, all hell breaks loose. If you try +to call it after a containing scope level exits, and if it refers +to some of the variables that are no longer in scope, you may be lucky, +but it’s not wise to take the risk. If, however, the nested function +does not refer to anything that has gone out of scope, you should be +safe. +</p> +<p>GCC implements taking the address of a nested function using a technique +called <em>trampolines</em>. This technique was described in +<cite>Lexical Closures for C++</cite> (Thomas M. Breuel, USENIX +C++ Conference Proceedings, October 17-21, 1988). +</p> +<p>A nested function can jump to a label inherited from a containing +function, provided the label is explicitly declared in the containing +function (see <a href="Local-Labels.html#Local-Labels">Local Labels</a>). Such a jump returns instantly to the +containing function, exiting the nested function that did the +<code>goto</code> and any intermediate functions as well. Here is an example: +</p> +<div class="smallexample"> +<pre class="smallexample">bar (int *array, int offset, int size) +{ + __label__ failure; + int access (int *array, int index) + { + if (index > size) + goto failure; + return array[index + offset]; + } + int i; + /* <span class="roman">…</span> */ + for (i = 0; i < size; i++) + /* <span class="roman">…</span> */ access (array, i) /* <span class="roman">…</span> */ + /* <span class="roman">…</span> */ + return 0; + + /* <span class="roman">Control comes here from <code>access</code> + if it detects an error.</span> */ + failure: + return -1; +} +</pre></div> + +<p>A nested function always has no linkage. Declaring one with +<code>extern</code> or <code>static</code> is erroneous. If you need to declare the nested function +before its definition, use <code>auto</code> (which is otherwise meaningless +for function declarations). +</p> +<div class="smallexample"> +<pre class="smallexample">bar (int *array, int offset, int size) +{ + __label__ failure; + auto int access (int *, int); + /* <span class="roman">…</span> */ + int access (int *array, int index) + { + if (index > size) + goto failure; + return array[index + offset]; + } + /* <span class="roman">…</span> */ +} +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Nonlocal-Gotos.html#Nonlocal-Gotos" accesskey="n" rel="next">Nonlocal Gotos</a>, Previous: <a href="Labels-as-Values.html#Labels-as-Values" accesskey="p" rel="previous">Labels as Values</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> |