用C++实现数据无损压缩、解压（使用LZW算法） - 图文

WriteCode(dest, 0); free(Omega.string); free(t.string); return BytePt; }

unsigned int LZWCoder::Decode(char *src, unsigned int *len, char *dest) {

unsigned int code, oldcode; TStr t, s; BytePt = 0; BitPt = 0; OutBytes = 0; t.string = NULL; t.len = 0; s.string = NULL; s.len = 0; InitStrTable();

while((code = GetNextCode(src)) != 257) {

if(code == 256) {

InitStrTable();

code = GetNextCode(src); if(code == 257) break; StrFromCode(&s, code); WriteString(dest, s); oldcode = code; } else {

if(code <= ItemPt) {

StrFromCode(&s, code); WriteString(dest, s); StrFromCode(&t, oldcode);

StrJoinChar(&t, s.string[0]); AddTableEntry(t); switch(ItemPt) {

case 511: Bits = 10; break; case 1023: Bits = 11; break; case 2047: Bits = 12; break; }

oldcode = code; } else {

StrFromCode(&s, oldcode); StrJoinChar(&s, s.string[0]); WriteString(dest, s); AddTableEntry(s); switch(ItemPt) {

case 511: Bits = 10; break; case 1023: Bits = 11; break; case 2047: Bits = 12; break; }

oldcode = code; } } }

free(t.string); free(s.string);

*len = BytePt + (BitPt != 0); return OutBytes; }

LZWCoder::LZWCoder() {

unsigned int i;

for(i = 0; i < 4097; i ++)

{

StrTable[i].string = NULL; StrTable[i].len = 0; } }

LZWCoder::~LZWCoder() {

unsigned int i;

for(i = 0; i < 4097; i ++) free(StrTable[i].string); } 用法：

LZWCoder *Coder; Coder = new LZWCoder(); 然后用

Coder->Encode(char *src, unsigned int len, char *dest); Coder->Decode(char *src, unsigned int *len, char *dest);

进行压缩或解压。Encode函数中，src是输入数据的指针，len是输入数据的长度，dest是输出数据的指针。函数返回输出数据的长度。Decode函数中各参数与Encode类似，但*len会返回解压过程使用了输入数据的字节数（一般等于压缩时输出数据的长度）。使用时把要压缩的数据分成每段8K来处理，效果会比较好。 算法实现没做优化，速度比较慢。