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diff --git a/share/doc/cpp/Obsolete-Features.html b/share/doc/cpp/Obsolete-Features.html new file mode 100644 index 0000000..4a64af5 --- /dev/null +++ b/share/doc/cpp/Obsolete-Features.html @@ -0,0 +1,175 @@ +<!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: Obsolete Features</title> + +<meta name="description" content="The C Preprocessor: Obsolete Features"> +<meta name="keywords" content="The C Preprocessor: Obsolete Features"> +<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="Implementation-Details.html#Implementation-Details" rel="up" title="Implementation Details"> +<link href="Invocation.html#Invocation" rel="next" title="Invocation"> +<link href="Implementation-limits.html#Implementation-limits" rel="previous" title="Implementation limits"> +<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="Obsolete-Features"></a> +<div class="header"> +<p> +Previous: <a href="Implementation-limits.html#Implementation-limits" accesskey="p" rel="previous">Implementation limits</a>, Up: <a href="Implementation-Details.html#Implementation-Details" accesskey="u" rel="up">Implementation Details</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="Obsolete-Features-1"></a> +<h3 class="section">11.3 Obsolete Features</h3> + +<p>CPP has some features which are present mainly for compatibility with +older programs. We discourage their use in new code. In some cases, +we plan to remove the feature in a future version of GCC. +</p> +<a name="Assertions"></a> +<h4 class="subsection">11.3.1 Assertions</h4> +<a name="index-assertions"></a> + +<p><em>Assertions</em> are a deprecated alternative to macros in writing +conditionals to test what sort of computer or system the compiled +program will run on. Assertions are usually predefined, but you can +define them with preprocessing directives or command-line options. +</p> +<p>Assertions were intended to provide a more systematic way to describe +the compiler’s target system and we added them for compatibility with +existing compilers. In practice they are just as unpredictable as the +system-specific predefined macros. In addition, they are not part of +any standard, and only a few compilers support them. +Therefore, the use of assertions is <strong>less</strong> portable than the use +of system-specific predefined macros. We recommend you do not use them at +all. +</p> +<a name="index-predicates"></a> +<p>An assertion looks like this: +</p> +<div class="smallexample"> +<pre class="smallexample">#<var>predicate</var> (<var>answer</var>) +</pre></div> + +<p><var>predicate</var> must be a single identifier. <var>answer</var> can be any +sequence of tokens; all characters are significant except for leading +and trailing whitespace, and differences in internal whitespace +sequences are ignored. (This is similar to the rules governing macro +redefinition.) Thus, <code>(x + y)</code> is different from <code>(x+y)</code> but +equivalent to <code>( x + y )<!-- /@w --></code>. Parentheses do not nest inside an +answer. +</p> +<a name="index-testing-predicates"></a> +<p>To test an assertion, you write it in an ‘<samp>#if</samp>’. For example, this +conditional succeeds if either <code>vax</code> or <code>ns16000</code> has been +asserted as an answer for <code>machine</code>. +</p> +<div class="smallexample"> +<pre class="smallexample">#if #machine (vax) || #machine (ns16000) +</pre></div> + +<p>You can test whether <em>any</em> answer is asserted for a predicate by +omitting the answer in the conditional: +</p> +<div class="smallexample"> +<pre class="smallexample">#if #machine +</pre></div> + +<a name="index-_0023assert"></a> +<p>Assertions are made with the ‘<samp>#assert</samp>’ directive. Its sole +argument is the assertion to make, without the leading ‘<samp>#</samp>’ that +identifies assertions in conditionals. +</p> +<div class="smallexample"> +<pre class="smallexample">#assert <var>predicate</var> (<var>answer</var>) +</pre></div> + +<p>You may make several assertions with the same predicate and different +answers. Subsequent assertions do not override previous ones for the +same predicate. All the answers for any given predicate are +simultaneously true. +</p> +<a name="index-assertions_002c-canceling"></a> +<a name="index-_0023unassert"></a> +<p>Assertions can be canceled with the ‘<samp>#unassert</samp>’ directive. It +has the same syntax as ‘<samp>#assert</samp>’. In that form it cancels only the +answer which was specified on the ‘<samp>#unassert</samp>’ line; other answers +for that predicate remain true. You can cancel an entire predicate by +leaving out the answer: +</p> +<div class="smallexample"> +<pre class="smallexample">#unassert <var>predicate</var> +</pre></div> + +<p>In either form, if no such assertion has been made, ‘<samp>#unassert</samp>’ has +no effect. +</p> +<p>You can also make or cancel assertions using command-line options. +See <a href="Invocation.html#Invocation">Invocation</a>. +</p> +<hr> +<div class="header"> +<p> +Previous: <a href="Implementation-limits.html#Implementation-limits" accesskey="p" rel="previous">Implementation limits</a>, Up: <a href="Implementation-Details.html#Implementation-Details" accesskey="u" rel="up">Implementation Details</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> |