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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/cpp/Conditionals.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
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diff --git a/share/doc/cpp/Conditionals.html b/share/doc/cpp/Conditionals.html new file mode 100644 index 0000000..d07835a --- /dev/null +++ b/share/doc/cpp/Conditionals.html @@ -0,0 +1,126 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1987-2023 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. A copy of +the license is included in the +section entitled "GNU Free Documentation License". + +This manual contains no Invariant Sections. The Front-Cover Texts are +(a) (see below), and the Back-Cover Texts are (b) (see below). + +(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>The C Preprocessor: Conditionals</title> + +<meta name="description" content="The C Preprocessor: Conditionals"> +<meta name="keywords" content="The C Preprocessor: Conditionals"> +<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="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="index.html#Top" rel="up" title="Top"> +<link href="Conditional-Uses.html#Conditional-Uses" rel="next" title="Conditional Uses"> +<link href="Newlines-in-Arguments.html#Newlines-in-Arguments" rel="previous" title="Newlines in Arguments"> +<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="Conditionals"></a> +<div class="header"> +<p> +Next: <a href="Diagnostics.html#Diagnostics" accesskey="n" rel="next">Diagnostics</a>, Previous: <a href="Macros.html#Macros" accesskey="p" rel="previous">Macros</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Conditionals-1"></a> +<h2 class="chapter">4 Conditionals</h2> +<a name="index-conditionals"></a> + +<p>A <em>conditional</em> is a directive that instructs the preprocessor to +select whether or not to include a chunk of code in the final token +stream passed to the compiler. Preprocessor conditionals can test +arithmetic expressions, or whether a name is defined as a macro, or both +simultaneously using the special <code>defined</code> operator. +</p> +<p>A conditional in the C preprocessor resembles in some ways an <code>if</code> +statement in C, but it is important to understand the difference between +them. The condition in an <code>if</code> statement is tested during the +execution of your program. Its purpose is to allow your program to +behave differently from run to run, depending on the data it is +operating on. The condition in a preprocessing conditional directive is +tested when your program is compiled. Its purpose is to allow different +code to be included in the program depending on the situation at the +time of compilation. +</p> +<p>However, the distinction is becoming less clear. Modern compilers often +do test <code>if</code> statements when a program is compiled, if their +conditions are known not to vary at run time, and eliminate code which +can never be executed. If you can count on your compiler to do this, +you may find that your program is more readable if you use <code>if</code> +statements with constant conditions (perhaps determined by macros). Of +course, you can only use this to exclude code, not type definitions or +other preprocessing directives, and you can only do it if the code +remains syntactically valid when it is not to be used. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="Conditional-Uses.html#Conditional-Uses" accesskey="1">Conditional Uses</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Conditional-Syntax.html#Conditional-Syntax" accesskey="2">Conditional Syntax</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Deleted-Code.html#Deleted-Code" accesskey="3">Deleted Code</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +</table> + +<hr> +<div class="header"> +<p> +Next: <a href="Diagnostics.html#Diagnostics" accesskey="n" rel="next">Diagnostics</a>, Previous: <a href="Macros.html#Macros" accesskey="p" rel="previous">Macros</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |