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document [imgName].src = imgOff; } }// --></SCRIPT></HEAD><BODY LANG="EN" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#6688AA" VLINK="#336688" ALINK="#808080"><A NAME="SEC51"></A><TABLE BORDER=0 CELLPADDING=0 CELLSPACING=10><TR VALIGN="TOP"><TD ALIGN="MIDDLE" WIDTH=50 BGCOLOR="#e6e6e6"><TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_50.html#SEC50" onMouseover="img_act('prev')" onMouseout="img_inact('prev')"><IMG SRC="prev.png" BORDER="0" ALT="Back: Fallback Function Implementations" ALIGN="MIDDLE" NAME="prev"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_52.html#SEC52" onMouseover="img_act('next')" onMouseout="img_inact('next')"><IMG SRC="next.png" BORDER="0" ALT="Forward: A Simple Shell Builders Library" ALIGN="MIDDLE" NAME="next"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"> <TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><IMG SRC="inactive.png" BORDER="0" ALT="FastBack: " ALIGN="MIDDLE" NAME="inactive"></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_45.html#SEC45" onMouseover="img_act('up')" onMouseout="img_inact('up')"><IMG SRC="up.png" BORDER="0" ALT="Up: GNU Autotools in Practice" ALIGN="MIDDLE" NAME="up"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_52.html#SEC52" onMouseover="img_act('forward')" onMouseout="img_inact('forward')"><IMG SRC="forward.png" BORDER="0" ALT="FastForward: A Simple Shell Builders Library" ALIGN="MIDDLE" NAME="forward"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook.html#SEC_Top" onMouseover="img_act('home')" onMouseout="img_inact('home')"><IMG SRC="home.png" BORDER="0" ALT="Top: Autoconf, Automake, and Libtool" ALIGN="MIDDLE" NAME="home"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_toc.html#SEC_Contents" onMouseover="img_act('toc')" onMouseout="img_inact('toc')"><IMG SRC="toc.png" BORDER="0" ALT="Contents: Table of Contents" ALIGN="MIDDLE" NAME="toc"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_285.html#SEC285" onMouseover="img_act('index')" onMouseout="img_inact('index')"><IMG SRC="index.png" BORDER="0" ALT="Index: Index" ALIGN="MIDDLE" NAME="index"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_abt.html#SEC_About" onMouseover="img_act('help')" onMouseout="img_inact('help')"><IMG SRC="help.png" BORDER="0" ALT="About: About this document" ALIGN="MIDDLE" NAME="help"></A></TD></TR></TABLE></TD><TD ALIGN="LEFT"><H3> 9.1.6 K&R Compilers </H3><!--docid::SEC51::--><P>K&R C is the name now used to describe the original C language specifiedby Brian Kernighan and Dennis Ritchie (hence, `<EM>K&R</EM>'). I haveyet to see a C compiler that doesn't support code written in the K&Rstyle, yet it has fallen very much into disuse in favor of the newerANSI C standard. Although it is increasingly common for vendors to<EM>unbundle</EM> their ANSI C compiler, the GCCproject<A NAME="DOCF11" HREF="autobook_fot.html#FOOT11">(11)</A> is available for all of the architectures I have everused.</P><P>There are four differences between the two C standards:</P><P><OL><LI>ANSI C expects full type specification in function prototypes, suchas you might supply in a library header file:<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>extern int functionname (const char *parameter1, size_t parameter 2);</pre></td></tr></table></P><P>The nearest equivalent in K&R style C is a forward declaration, whichallows you to use a function before its corresponding definition:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>extern int functionname ();</pre></td></tr></table></P><P>As you can imagine, K&R has very bad type safety, and does not performany checks that only function arguments of the correct type are used.</P><P><LI>The function headers of each function definition are writtendifferently. Where you might see the following written in ANSI C:<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>intfunctionname (const char *parameter1, size_t parameter2){ ...}</pre></td></tr></table></P><P>K&R expects the parameter type declarations separately, like this:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>intfunctionname (parameter1, parameter2) const char *parameter1; size_t parameter2;{ ...}</pre></td></tr></table></P><P><LI>There is no concept of an untyped pointer in K&R C. Where you might beused to seeing <SAMP>`void *'</SAMP> pointers in ANSI code, you are forcedto overload the meaning of <SAMP>`char *'</SAMP> for K&R compilers.<P><LI>Variadic functions are handled with a different API in K&R C,imported with <SAMP>`#include <varargs.h>'</SAMP>. A K&R variadic functiondefinition looks like this:<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>intfunctionname (va_alist) va_dcl{⌨️ 快捷键说明
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