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<HTML><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><!-- Created on September, 12 2004 by texi2html 1.64 --><!-- Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author) Karl Berry <karl@freefriends.org> Olaf Bachmann <obachman@mathematik.uni-kl.de> and many others.Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>Send bugs and suggestions to <texi2html@mathematik.uni-kl.de> --><HEAD><TITLE>Autoconf, Automake, and Libtool: C Data Type Sizes</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: C Data Type Sizes"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: C Data Type Sizes"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META NAME="Generator" CONTENT="texi2html 1.64"><script language="Javascript"><!-- // Check the browser version. function checkVersion() { if (navigator.appVersion.charAt(0)>=3) return true; if (navigator.appVersion.charAt(0)>=4) return true; else return false; 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As of this writing, this mainly matters for thetypes <CODE>int</CODE> and <CODE>long</CODE>. A variable of type <CODE>int</CODE> must beat least 16 bits, and is often 32 bits. A variable of type <CODE>long</CODE>must be at least 32 bits, and is sometimes 64 bits.</P><P>The range of a 16 bit number is -32768 to 32767 for a signed number, or0 to 65535 for an unsigned number. If a variable may hold numberslarger than 16 bits, use <CODE>long</CODE> rather than <CODE>int</CODE>. Neverassume that <CODE>int</CODE> or <CODE>long</CODE> have a specific size, or that theywill overflow at a particular point. When appropriate, use variables ofsystem defined types rather than <CODE>int</CODE> or <CODE>long</CODE>:</P><P><DL COMPACT><DT><CODE>size_t</CODE><DD>Use this to hold the size of an object, as returned by <CODE>sizeof</CODE>.<DT><CODE>ptrdiff_t</CODE><DD>Use this to hold the difference between two pointers into the samearray.<DT><CODE>time_t</CODE><DD>Use this to hold a time value as returned by the <CODE>time</CODE> function.<DT><CODE>off_t</CODE><DD>On a Unix system, use this to hold a file position as returned by<CODE>lseek</CODE>.<DT><CODE>ssize_t</CODE><DD>Use this to hold the result of the Unix <CODE>read</CODE> or <CODE>write</CODE>functions.</DL><P>Some books on C recommend using typedefs to specify types of particularsizes, and then adjusting those typedefs on specific systems.GNU Autotools supports this using the <SAMP>`AC_CHECK_SIZEOF'</SAMP> macro.However, while we agree with using typedefs for clarity, we do notrecommend using them purely for portability. It is safest to rely onlyon the minimum size assumptions made by the C language, rather than toassume that a type of a specific size will always be available. Also,most C compilers will define <CODE>int</CODE> to be the most efficient typefor the system, so it is normally best to simply use <CODE>int</CODE> whenpossible.</P><P><A NAME="C Endianness"></A></TR></TABLE><BR> <FONT SIZE="-1">This document was generatedby <I>Gary V. Vaughan</I> on <I>September, 12 2004</I>using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html"><I>texi2html</I></A></BODY></HTML>⌨️ 快捷键说明
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