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diff --git a/share/doc/cppinternals/Line-Numbering.html b/share/doc/cppinternals/Line-Numbering.html new file mode 100644 index 0000000..606a8b0 --- /dev/null +++ b/share/doc/cppinternals/Line-Numbering.html @@ -0,0 +1,158 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The GNU C Preprocessor Internals: Line Numbering</title> + +<meta name="description" content="The GNU C Preprocessor Internals: Line Numbering"> +<meta name="keywords" content="The GNU C Preprocessor Internals: Line Numbering"> +<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="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="index.html#Top" rel="up" title="Top"> +<link href="Guard-Macros.html#Guard-Macros" rel="next" title="Guard Macros"> +<link href="Token-Spacing.html#Token-Spacing" rel="previous" title="Token Spacing"> +<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="Line-Numbering"></a> +<div class="header"> +<p> +Next: <a href="Guard-Macros.html#Guard-Macros" accesskey="n" rel="next">Guard Macros</a>, Previous: <a href="Token-Spacing.html#Token-Spacing" accesskey="p" rel="previous">Token Spacing</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="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Line-numbering"></a> +<h2 class="unnumbered">Line numbering</h2> +<a name="index-line-numbers"></a> + +<a name="Just-which-line-number-anyway_003f"></a> +<h3 class="section">Just which line number anyway?</h3> + +<p>There are three reasonable requirements a cpplib client might have for +the line number of a token passed to it: +</p> +<ul> +<li> The source line it was lexed on. +</li><li> The line it is output on. This can be different to the line it was +lexed on if, for example, there are intervening escaped newlines or +C-style comments. For example: + +<div class="smallexample"> +<pre class="smallexample">foo /* <span class="roman">A long +comment</span> */ bar \ +baz +⇒ +foo bar baz +</pre></div> + +</li><li> If the token results from a macro expansion, the line of the macro name, +or possibly the line of the closing parenthesis in the case of +function-like macro expansion. +</li></ul> + +<p>The <code>cpp_token</code> structure contains <code>line</code> and <code>col</code> +members. The lexer fills these in with the line and column of the first +character of the token. Consequently, but maybe unexpectedly, a token +from the replacement list of a macro expansion carries the location of +the token within the <code>#define</code> directive, because cpplib expands a +macro by returning pointers to the tokens in its replacement list. The +current implementation of cpplib assigns tokens created from built-in +macros and the ‘<samp>#</samp>’ and ‘<samp>##</samp>’ operators the location of the most +recently lexed token. This is a because they are allocated from the +lexer’s token runs, and because of the way the diagnostic routines infer +the appropriate location to report. +</p> +<p>The diagnostic routines in cpplib display the location of the most +recently <em>lexed</em> token, unless they are passed a specific line and +column to report. For diagnostics regarding tokens that arise from +macro expansions, it might also be helpful for the user to see the +original location in the macro definition that the token came from. +Since that is exactly the information each token carries, such an +enhancement could be made relatively easily in future. +</p> +<p>The stand-alone preprocessor faces a similar problem when determining +the correct line to output the token on: the position attached to a +token is fairly useless if the token came from a macro expansion. All +tokens on a logical line should be output on its first physical line, so +the token’s reported location is also wrong if it is part of a physical +line other than the first. +</p> +<p>To solve these issues, cpplib provides a callback that is generated +whenever it lexes a preprocessing token that starts a new logical line +other than a directive. It passes this token (which may be a +<code>CPP_EOF</code> token indicating the end of the translation unit) to the +callback routine, which can then use the line and column of this token +to produce correct output. +</p> +<a name="Representation-of-line-numbers"></a> +<h3 class="section">Representation of line numbers</h3> + +<p>As mentioned above, cpplib stores with each token the line number that +it was lexed on. In fact, this number is not the number of the line in +the source file, but instead bears more resemblance to the number of the +line in the translation unit. +</p> +<p>The preprocessor maintains a monotonic increasing line count, which is +incremented at every new line character (and also at the end of any +buffer that does not end in a new line). Since a line number of zero is +useful to indicate certain special states and conditions, this variable +starts counting from one. +</p> +<p>This variable therefore uniquely enumerates each line in the translation +unit. With some simple infrastructure, it is straight forward to map +from this to the original source file and line number pair, saving space +whenever line number information needs to be saved. The code the +implements this mapping lies in the files <samp>line-map.cc</samp> and +<samp>line-map.h</samp>. +</p> +<p>Command-line macros and assertions are implemented by pushing a buffer +containing the right hand side of an equivalent <code>#define</code> or +<code>#assert</code> directive. Some built-in macros are handled similarly. +Since these are all processed before the first line of the main input +file, it will typically have an assigned line closer to twenty than to +one. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Guard-Macros.html#Guard-Macros" accesskey="n" rel="next">Guard Macros</a>, Previous: <a href="Token-Spacing.html#Token-Spacing" accesskey="p" rel="previous">Token Spacing</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="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |