| <html lang="en"> |
| <head> |
| <title>Formatted Output Basics - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Formatted-Output.html#Formatted-Output" title="Formatted Output"> |
| <link rel="next" href="Output-Conversion-Syntax.html#Output-Conversion-Syntax" title="Output Conversion Syntax"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 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 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <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="Formatted-Output-Basics"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Output-Conversion-Syntax.html#Output-Conversion-Syntax">Output Conversion Syntax</a>, |
| Up: <a rel="up" accesskey="u" href="Formatted-Output.html#Formatted-Output">Formatted Output</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">12.12.1 Formatted Output Basics</h4> |
| |
| <p>The <code>printf</code> function can be used to print any number of arguments. |
| The template string argument you supply in a call provides |
| information not only about the number of additional arguments, but also |
| about their types and what style should be used for printing them. |
| |
| <p>Ordinary characters in the template string are simply written to the |
| output stream as-is, while <dfn>conversion specifications</dfn> introduced by |
| a ‘<samp><span class="samp">%</span></samp>’ character in the template cause subsequent arguments to be |
| formatted and written to the output stream. For example, |
| <a name="index-conversion-specifications-_0028_0040code_007bprintf_007d_0029-1019"></a> |
| <pre class="smallexample"> int pct = 37; |
| char filename[] = "foo.txt"; |
| printf ("Processing of `%s' is %d%% finished.\nPlease be patient.\n", |
| filename, pct); |
| </pre> |
| <p class="noindent">produces output like |
| |
| <pre class="smallexample"> Processing of `foo.txt' is 37% finished. |
| Please be patient. |
| </pre> |
| <p>This example shows the use of the ‘<samp><span class="samp">%d</span></samp>’ conversion to specify that |
| an <code>int</code> argument should be printed in decimal notation, the |
| ‘<samp><span class="samp">%s</span></samp>’ conversion to specify printing of a string argument, and |
| the ‘<samp><span class="samp">%%</span></samp>’ conversion to print a literal ‘<samp><span class="samp">%</span></samp>’ character. |
| |
| <p>There are also conversions for printing an integer argument as an |
| unsigned value in octal, decimal, or hexadecimal radix (‘<samp><span class="samp">%o</span></samp>’, |
| ‘<samp><span class="samp">%u</span></samp>’, or ‘<samp><span class="samp">%x</span></samp>’, respectively); or as a character value |
| (‘<samp><span class="samp">%c</span></samp>’). |
| |
| <p>Floating-point numbers can be printed in normal, fixed-point notation |
| using the ‘<samp><span class="samp">%f</span></samp>’ conversion or in exponential notation using the |
| ‘<samp><span class="samp">%e</span></samp>’ conversion. The ‘<samp><span class="samp">%g</span></samp>’ conversion uses either ‘<samp><span class="samp">%e</span></samp>’ |
| or ‘<samp><span class="samp">%f</span></samp>’ format, depending on what is more appropriate for the |
| magnitude of the particular number. |
| |
| <p>You can control formatting more precisely by writing <dfn>modifiers</dfn> |
| between the ‘<samp><span class="samp">%</span></samp>’ and the character that indicates which conversion |
| to apply. These slightly alter the ordinary behavior of the conversion. |
| For example, most conversion specifications permit you to specify a |
| minimum field width and a flag indicating whether you want the result |
| left- or right-justified within the field. |
| |
| <p>The specific flags and modifiers that are permitted and their |
| interpretation vary depending on the particular conversion. They're all |
| described in more detail in the following sections. Don't worry if this |
| all seems excessively complicated at first; you can almost always get |
| reasonable free-format output without using any of the modifiers at all. |
| The modifiers are mostly used to make the output look “prettier” in |
| tables. |
| |
| </body></html> |
| |
