| <html lang="en"> |
| <head> |
| <title>Deleted Code - The C Preprocessor</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The C Preprocessor"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Conditionals.html#Conditionals" title="Conditionals"> |
| <link rel="prev" href="Conditional-Syntax.html#Conditional-Syntax" title="Conditional Syntax"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, |
| 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, |
| 2008, 2009, 2010 |
| 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 1.2 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. |
| --> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Deleted-Code"></a> |
| <p> |
| Previous: <a rel="previous" accesskey="p" href="Conditional-Syntax.html#Conditional-Syntax">Conditional Syntax</a>, |
| Up: <a rel="up" accesskey="u" href="Conditionals.html#Conditionals">Conditionals</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">4.3 Deleted Code</h3> |
| |
| <p><a name="index-commenting-out-code-92"></a> |
| If you replace or delete a part of the program but want to keep the old |
| code around for future reference, you often cannot simply comment it |
| out. Block comments do not nest, so the first comment inside the old |
| code will end the commenting-out. The probable result is a flood of |
| syntax errors. |
| |
| <p>One way to avoid this problem is to use an always-false conditional |
| instead. For instance, put <code>#if 0</code> before the deleted code and |
| <code>#endif</code> after it. This works even if the code being turned |
| off contains conditionals, but they must be entire conditionals |
| (balanced ‘<samp><span class="samp">#if</span></samp>’ and ‘<samp><span class="samp">#endif</span></samp>’). |
| |
| <p>Some people use <code>#ifdef notdef</code> instead. This is risky, because |
| <code>notdef</code> might be accidentally defined as a macro, and then the |
| conditional would succeed. <code>#if 0</code> can be counted on to fail. |
| |
| <p>Do not use <code>#if 0</code> for comments which are not C code. Use a real |
| comment, instead. The interior of <code>#if 0</code> must consist of complete |
| tokens; in particular, single-quote characters must balance. Comments |
| often contain unbalanced single-quote characters (known in English as |
| apostrophes). These confuse <code>#if 0</code>. They don't confuse |
| ‘<samp><span class="samp">/*</span></samp>’. |
| |
| </body></html> |
| |
