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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>Rationale</title></head><body><basefont size="3"> <center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group</font></center><hr size="2" noshade><h3><a name="tag_01_05"></a>File Format Notation</h3><p>The notation for spaces allows some flexibility for application output. Note that an empty character position in <i>format</i>represents one or more <blank>s on the output (not <i>white space</i>, which can include <newline>s). Therefore,another utility that reads that output as its input must be prepared to parse the data using <a href="../functions/scanf.html"><i>scanf</i>()</a>, <a href="../utilities/awk.html"><i>awk</i></a>, and so on. The <tt>'<img src="../images/delta.gif" border="0">'</tt> character is used when exactly one <space> is output.</p><p>The treatment of integers and spaces is different from the <a href="../functions/printf.html"><i>printf</i>()</a> function inthat they can be surrounded with <blank>s. This was done so that, given a format such as:</p><blockquote><pre><tt>"%d\n",<</tt><i>foo</i><tt>></tt></pre></blockquote><p>the implementation could use a <a href="../functions/printf.html"><i>printf</i>()</a> call such as:</p><blockquote><pre><tt>printf("%6d\n", foo);</tt></pre></blockquote><p>and still conform. This notation is thus somewhat like <a href="../functions/scanf.html"><i>scanf</i>()</a> in addition to <ahref="../functions/printf.html"><i>printf</i>()</a>.</p><p>The <a href="../functions/printf.html"><i>printf</i>()</a> function was chosen as a model because most of the standarddevelopers were familiar with it. One difference from the C function <a href="../functions/printf.html"><i>printf</i>()</a> is thatthe <tt>l</tt> and <tt>h</tt> conversion specifier characters are not used. As expressed by the Shell and Utilities volume ofIEEE Std 1003.1-2001, there is no differentiation between decimal values for type <b>int</b>, type <b>long</b>, or type<b>short</b>. The conversion specifications <tt>%d</tt> or <tt>%i</tt> should be interpreted as an arbitrary length sequence ofdigits. Also, no distinction is made between single precision and double precision numbers ( <b>float</b> or <b>double</b> in C).These are simply referred to as floating-point numbers.</p><p>Many of the output descriptions in the Shell and Utilities volume of IEEE Std 1003.1-2001 use the term ``line'', suchas:</p><blockquote><pre><tt>"%s", <input line></tt></pre></blockquote><p>Since the definition of <i>line</i> includes the trailing <newline> already, there is no need to include a <tt>'\n'</tt>in the format; a double <newline> would otherwise result.</p><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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