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<!DOCTYPE HTML PUBLIC "html.dtd"><HTML><HEAD><TITLE>The Data Compression Book-:The Dawn Age: Minimum Redundancy Coding</TITLE><META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW"><SCRIPT><!--function displayWindow(url, width, height) { var Win = window.open(url,"displayWindow",'width=' + width +',height=' + height + ',resizable=1,scrollbars=yes');}//--></SCRIPT></HEAD><BODY BGCOLOR="#FFFFFF" VLINK="#DD0000" TEXT="#000000" LINK="#DD0000" ALINK="#FF0000"><TD WIDTH="540" VALIGN="TOP"><!-- <CENTER><TABLE><TR><TD><FORM METHOD="GET" ACTION="http://search.itknowledge.com/excite/cgi-bin/AT-foldocsearch.cgi"><INPUT NAME="search" SIZE="20" VALUE=""><BR><CENTER><INPUT NAME="searchButton" TYPE="submit" VALUE="Glossary Search"></CENTER><INPUT NAME="source" TYPE="hidden" VALUE="local" CHECKED> <INPUT NAME="bltext" TYPE="hidden" VALUE="Back to Search"><INPUT NAME="sp" TYPE="hidden" VALUE="sp"></FORM></TD><TD><IMG SRC="http://www.itknowledge.com/images/dotclear.gif" WIDTH="15" HEIGHT="1"></TD><TD><FORM METHOD="POST" ACTION="http://search.itknowledge.com/excite/cgi-bin/AT-subscriptionsearch.cgi"><INPUT NAME="search" SIZE="20" VALUE=""><BR><CENTER><INPUT NAME="searchButton" TYPE="submit" VALUE=" Book Search "></CENTER><INPUT NAME="source" TYPE="hidden" VALUE="local" CHECKED> <INPUT NAME="backlink" TYPE="hidden" VALUE="http://search.itknowledge.com:80/excite/AT-subscriptionquery.html"><INPUT NAME="bltext" TYPE="hidden" VALUE="Back to Search"><INPUT NAME="sp" TYPE="hidden" VALUE="sp"></FORM></TD></TR></TABLE></CENTER> --><!-- ISBN=1558514341//--><!-- TITLE=The Data Compression Book-//--><!-- AUTHOR=Mark Nelson//--><!-- PUBLISHER=IDG Books Worldwide, Inc.//--><!-- IMPRINT=M & T Books//--><!-- CHAPTER=3//--><!-- PAGES=046-050//--><!-- UNASSIGNED1//--><!-- UNASSIGNED2//--><CENTER><TABLE BORDER><TR><TD><A HREF="043-046.html">Previous</A></TD><TD><A HREF="../ewtoc.html">Table of Contents</A></TD><TD><A HREF="050-054.html">Next</A></TD></TR></TABLE></CENTER><P><BR></P><P>In MAIN-C.C, a compression module supplies three things: a Usage string, which can print out a list of parameters, etc.; a CompressionName string, which lets the MAIN-C.C program print out the compression method; and a CompressFile() routine, which actually compresses the file. In this chapter, these routines are in a file called HUFF.C, which implements an order 0 model with a Huffman coder. MAIN-C.C is shown below.</P><!-- CODE //--><PRE>/*********************** Start of MAIN-C.C **********************//** This is the driver program used when testing compression algorithms.* In order to cut back on repetitive code, this version of main is* used with all of the compression routines. In order to turn it into* a real program, it needs to have another module that supplies one* routine and two strings, namely:** void CompressFile( FILE *input, BIT_FILE *output,* int argc, char *argv );* char *Usage;* char *CompressionName;** The main() routine supplied here has the job of checking for valid* input and output files, opening them, and then calling the* compression routine. If the files are not present, or no arguments* are supplied, it prints out an error message, which includes the* Usage string supplied by the compression module. All of the* routines and strings needed by this routine are defined in the* main.h header file.** After this is built into a compression program of any sort, the* program can be called like this:** main-c infile outfile [ options ]**/#include <stdio.h>#include <stdlib.h>#include <string.h>#include "bitio.h"#include "errhand.h"#include "main.h"#ifdef ___STDC___void usage_exit( char *prog_name );void print_ratios( char *input, char *output );long file_size( char *name );#elsevoid usage_exit();void print_ratios();long file_size();#endifint main( argc, argv )int argc;char *argv[];{ BIT_FILE *ouput; FILE *input; setbuf( stdout, NULL ); if ( argc < 3 ) usage_exit( argv[ 0 ] ); input = fopen(argv [ 1 ], "rb" ); if ( input == NULL ) fatal_error( "Error opening %s for input/n", argv[ 1 ] ); output = OpenOutputBitFile( argv[ 2 ] ); if ( output == NULL ) fatal error( "Error opening %s for input/n", argv[ 2 ] ); printf( "\nCompressing %s to %s\n", argv[ 1 ], argv[ 2 ] ); printf( "Using %s\n, CompressionName ); argc -= 3; argv += 3; CompressFile( input, output, argc, argv ); CloseOutputBitFile( output ); fclose( input ); print_ratios( argv[ 1 ], argv[ 2 ] ); return( 0 );}/** This routine just wants to print out the usage message that is* called for when the program is run with no parameters. The first* part of the Usage statement is supposed to be just the program* name. argv[ 0 ] generally holds the fully qualified path name* of the program being run. I make a half-hearted attempt to strip* out that path info and file extension before printing it. It should* get the general idea across.*/void usage_exit( prog_name )char *prog_name;{ char *short_name; char *extension; short_name = strrchr( prog_name, '\\' ); if (short_name == NULL ) short_name = strrchr( prog_name, '/' ); if (short_name == NULL ) short_name = strrchr( prog_name, ':' ); if (short_name != NULL ) short_name++; else short_name = prog_name; extension = strrchr( short_name, '.' ); if ( extension != NULL ) *extension = '\0'; printf( "\nUsage: %s %s\n", short_name, Usage ); exit( 0 );}/** This routine is used by main to get the size of a file after it has* been closed. It does all the work, and returns a long. The main* program gets the file size for the plain text, and the size of the* compressed file, and prints the ratio.*/#ifndef SEEK_END#define SEEK_END 2#endiflong file_size( name )char *name;{ long eof ftell; FILE *file; file = fopen( name, "r"); if ( file == NULL ) return( OL ); fseek( file, OL, SEEK_END ); eof_ftell = ftell( file ); fclose( file ); return( eof_ftell );}/** This routine prints out the compression ratios after the input and* output files have been closed.*/void print_ratios( input, output )char *input;char *output;{ long input_size; long output_size; int ratio; input_size = file_size( input ); if ( input_size == 0 ) input_size = 1; output_size = file_size * 100L / input_size ); ratio = 100 - (int) ( output_size * 100L / input_size ); printf( "\nInput bytes: %ld\n", input_size ); printf( "Output bytes: %ld/n", output_size ); if ( output_size == 0 ) output_size = 1; printf( "Compression ratio: %d%%\n", ratio );/*********************** End of MAIN-C.C *************************/</PRE><!-- END CODE //--><P><BR></P><CENTER><TABLE BORDER><TR><TD><A HREF="043-046.html">Previous</A></TD><TD><A HREF="../ewtoc.html">Table of Contents</A></TD><TD><A HREF="050-054.html">Next</A></TD></TR></TABLE></CENTER></TD></TR></TABLE></BODY></HTML>⌨️ 快捷键说明
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