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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN"><!-- This collection of hypertext pages is Copyright 1995-2005 by Steve Summit. --><!-- Content from the book "C Programming FAQs: Frequently Asked Questions" --><!-- (Addison-Wesley, 1995, ISBN 0-201-84519-9) is made available here by --><!-- permission of the author and the publisher as a service to the community. --><!-- It is intended to complement the use of the published text --><!-- and is protected by international copyright laws. --><!-- The on-line content may be accessed freely for personal use --><!-- but may not be published or retransmitted without explicit permission. --><!-- --><!-- this page built Sat Dec 24 21:47:47 2005 by faqproc version 2.7 --><!-- from source file miscbits.sgml dated Wed Dec 21 13:02:12 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/misc/hexio.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:04 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 20.10</title><link href="byteswap.html" rev=precedes><link href="base2.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="byteswap.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="base2.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../index-2.html"><img src="../images/buttontop.gif" alt="top/contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><hr><p><!-- qbegin --><h1>comp.lang.c FAQ list<font color=blue>·</font><!-- qtag -->Question 20.10</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I convert integers tobinary orhexadecimal?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Make sure you really know what you're asking.Integers are stored internally in binary,although for most purposes it is not incorrectto think of them as being inoctal, decimal, or hexadecimal,whichever is convenient.The base in which a number is expressed matters only when thatnumber is read in from or written out to the outside world,either in the form ofa source code constantor in the form of I/Operformed by a program.</p><p>In source code,a non-decimal base is indicatedbya leading <TT>0</TT> or <TT>0x</TT>(for octal or hexadecimal, respectively).During I/O, the base of a formatted number is controlledin the<TT>printf</TT>and <TT>scanf</TT>familyof functionsby the choice of format specifier(<TT>%d</TT>, <TT>%o</TT>, <TT>%x</TT>, etc.)and in the <TT>strtol</TT>and <TT>strtoul</TT>functionsby the third argument.During<em>binary</em> I/O,however, the base again becomes immaterial:if numbers are being read or written as individual bytes(typically with <TT>getc</TT> or <TT>putc</TT>),or as multi-byte words(typically with <TT>fread</TT> or <TT>fwrite</TT>),it is meaningless to ask what ``base'' they are in.</p><p>If what you need is formatted binary conversion,it's easy enough to do.Here is a little functionfor formattinga number in a requested base:<pre>char *baseconv(unsigned int num, int base){ static char retbuf[33]; char *p; if(base < 2 || base > 16) return NULL; p = &retbuf[sizeof(retbuf)-1]; *p = '\0'; do { *--p = "0123456789abcdef"[num % base]; num /= base; } while(num != 0); return p;}</pre>(Note that this function, as written,returns a pointer to static data,such that only one of its return values can be used at a time;see question <a href="../malloc/retaggr.html">7.5a</a>.A better size for the <TT>retbuf</TT> arraywould be <TT>sizeof(int)*CHAR_BIT+1</TT>;see question <a href="../stdio/sprintfsize.html">12.21</a>.)</p><p>For more information about ``binary'' I/O,seequestions <a href="../struct/io.html">2.11</a>, <a href="../stdio/binaryio.html">12.37</a>, and <a href="../stdio/extconform.html">12.42</a>.See also questions<a href="../charstring/asciivals.html">8.6</a>and<a href="../lib/itoa.html">13.1</a>.</p><p>Additional links:A<a href="btod.html">long reply</a>I sent to someone who was asking how to write a``binary to decimal'' conversion function</p><p>References:ISO Secs. 7.10.1.5,7.10.1.6<br></p><!-- aend --><p><hr><a href="byteswap.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="base2.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../questions.html"><img src="../images/buttontop.gif" alt="contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><br><!-- lastfooter --><a href="../about.html">about this FAQ list</a> <a href="../eskimo.html">about eskimo</a> <a href="../search.html">search</a> <a href="../feedback.html">feedback</a> <a href="copyright.html">copyright</a><p>Hosted by<a href="http://www.eskimo.com/"><img src="../../www.eskimo.com/img/link/eskitiny.gif" alt="Eskimo North"></a></body><!-- Mirrored from c-faq.com/misc/hexio.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:05 GMT --></html>⌨️ 快捷键说明
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