lzw2.cpp

关于压缩与解压缩的源码 自己编的 适合数据结构学习 用到了散列

#include"LZW2.h"

#define codes 16777216
#define ByteSize 8
#define excess 4
#define alpha 256
#define mask 15

unsigned char s[codes];
unsigned int size;
int LeftOver;
int status=0;
element ht[codes];
ifstream in;
ofstream out;

void SetFiles(int argc,char*argv[])
{
	char OutputFile[50],InputFile[50];
	if(argc>=2)strcpy(InputFile,argv[1]);
	else
	{
		cout<<"Enter name of file to compress"<<endl;
		cout<<"Omit the extension .zzz"<<endl;
		cin>>InputFile;
	}
	if(strchr(InputFile,'.'))
	{
        cerr<<"File name has extension"<<endl;
		exit(1);
	}

	if(in.fail())
	{
		cerr<<"Cannot open"<<InputFile<<endl;
		exit(1);
	}
	strcpy(OutputFile,InputFile);
	strcat(InputFile,".zzz");
	in.open(InputFile,ios::binary);	
	strcat(OutputFile,".txt");
	out.open(OutputFile,ios::binary);
}

void Output(unsigned long code)
{
	size=-1;
	while(code>=alpha)
	{
		s[++size]=ht[code].suffix;
	    code=ht[code].prefix;
	}
	s[++size]=(char)code;
	for(int i=size;i>=0;i--)
		out.put(s[i]);
}

bool GetCode(unsigned long& code)
{
	unsigned char c,d,e;
	in.get(c);
	//cout<<c<<" ";
	if(in.eof())return false;
	in.get(d);
	if(status)code=(LeftOver<<ByteSize*2)|(c<<ByteSize)|d;
	else
	{
		in.get(e);
		//cout<<d<<endl;
		code=(c<<excess+ByteSize)|(d<<excess)|(e>>excess);
		LeftOver=e&mask;
	}
	status=1-status;
	return true;
}

void Decompress()
{
	unsigned long used=alpha;
	unsigned long pcode;
	unsigned long ccode;
	if(GetCode(pcode))
	{
		s[0]=(char)pcode;
		out.put(s[0]);
		size=0;

	    while(GetCode(ccode))
		{
		    if(ccode<used)
			{
			    Output(ccode);
                if(used<codes)
				{
				    ht[used].prefix=pcode;
				    ht[used++].suffix=s[size];
				}
			}
		    else
			{
			    ht[used].prefix=pcode;
			    ht[used++].suffix=s[size];
			    Output(ccode);
			}
		    pcode=ccode;
		}
	}
	out.close();
	in.close();
}

void main(int argc,char*argv[])
{
	SetFiles(argc,argv);
	Decompress();
}