使用Zlib实现压缩和解压缩

墨蓝 2022-08-13 14:41 311阅读 0赞

压缩流程:  
1.使用zlib做压缩,先调用deflateInit(),这个函数必须在使用deflate之前,zalloc,zfree和opaque等字段都是在deflateInit被初始化

的,deflateInit将分配按照顺序分配内存空间,每次分配256K

2.deflateInit有-1 到 9的几个压缩级别,低压缩级别可以获得更快的执行,但是压缩比例低,Z\_DEFAULT\_COMPRESSION为-1,平衡压缩比例与

速度可以把Level设为6,Level 0实际上没有压缩.另外你也可以使用deflateInit2()来代替DeflateInit().

3.设计一个循环压缩数据,里面只掉用一次deflate(),并且在循环末尾检测是否到达文件底部.

4.读入文件,读入的byte量放到avail\_in里面,next\_in存放指向这些的字节的指针,使用feof()检测是否到底,为了防止发生任何内存泄漏,请

使用delateEnd()

5.内部循环将我们读入的数据压缩,当没有数据可以压缩的时候,avail\_in里面的值为0.

6.avail\_out指向压缩数据量大小,next\_out指向压缩的数据

7.调用deflate(),该函数第二个参数如果为Z\_NO\_FLUSH的时候数据处于压缩状态,一但为Z\_FINISH,deflate()将把压缩数据传到输出

流,deflate的返回值为Z\_OK和Z\_STREAM\_END是正确的

解压缩流程:  
1.初始化z\_stream与压缩过程相同,但是不用设定压缩level,avail\_in和next\_in需要在inflateInit()之前初始化

2.读入数据填充strm结构,如果到达文件尾跳出外围循环并报告一个Error

3.内层循环实现与压缩相同的功能,将所有输入数据解压成输出数据

4.调用inflate()函数,这里不需要调整flush参数,但要注意inflate的返回值.

代码:

#include "zconf.h"
    #include "zlib.h"
    #include <string.h>
    // The one and only application object
    
    CWinApp theApp;
    
    using namespace std;
    
    #if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
    #  include <fcntl.h>
    #  include <io.h>
    #  define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
    #else
    #  define SET_BINARY_MODE(file)
    #endif
    
    #define CHUNK 16384
    int def(FILE * source, FILE *dest, int level)
    {
     int ret, flush;
     unsigned have;
     z_stream strm;
     unsigned char in[CHUNK];
     unsigned char out[CHUNK];
     /*allocate defalte state*/
     strm.zalloc = Z_NULL;
     strm.zfree = Z_NULL;
     strm.opaque = Z_NULL;
     ret = deflateInit(&strm,level);
     if (ret != Z_OK)
      return ret;
     
     do 
     {
      strm.avail_in = fread (in, 1, CHUNK, source);
      if (ferror(source))
      {
       (void)deflateEnd(&strm);
       return Z_ERRNO;
      }
      flush = feof(source)?Z_FINISH:Z_NO_FLUSH;
      strm.next_in = in;
      do
      {
       strm.avail_out = CHUNK;
       strm.next_out = out;
       ret = deflate(&strm,flush);
       have = CHUNK - strm.avail_out;
       if (fwrite(out,1,have,dest) != have || ferror(dest))
       {
        (void)deflateEnd(&strm);
        return Z_ERRNO;
       }
       //The way we tell that deflate() has no more output is by seeing that it did not fill the output
    
    buffer,
       //leaving avail_out greater than zero.
      }while(strm.avail_out == 0);
     }while(flush != Z_FINISH);
     (void)deflateEnd(&strm);
     return Z_OK;
    }
    
    int inf(FILE * source, FILE * dest)
    {
     int ret;
     unsigned have;
     z_stream strm;
     unsigned char in[CHUNK];
     unsigned char out[CHUNK];
    
     strm.zalloc = Z_NULL;
     strm.zfree = Z_NULL;
     strm.opaque = Z_NULL;
     strm.avail_in = 0;
     strm.next_in = Z_NULL;
     ret = inflateInit(&strm);
     if (ret != Z_OK)
      return ret;
     do
     {
      strm.avail_in = fread(in,1,CHUNK,source);
      if (ferror(source))
      {
       (void)inflateEnd(&strm);
       return Z_ERRNO;
      }
      if (0 == strm.avail_in)
       break;
      strm.next_in = in;
      do
      {
       strm.avail_out = CHUNK;
       strm.next_out = out;
    
       ret = inflate(&strm, Z_NO_FLUSH);
       switch(ret)
       {
        case Z_NEED_DICT:
         ret = Z_DATA_ERROR;
        case Z_DATA_ERROR:
        case Z_MEM_ERROR:
         (void)inflateEnd(&strm);
         return ret;
       }
       have = CHUNK - strm.avail_out;
       if (fwrite(out,1,have,dest) != have || ferror(dest))
       {
        (void)inflateEnd(&strm);
        return Z_ERRNO;
       }
      }while (strm.avail_out == 0);
     }while(ret != Z_STREAM_END);
     (void)inflateEnd(&strm);
     return ret = Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
    }
    
    void zerr(int ret)
    {
        fputs("zpipe: ", stderr);
        switch (ret) {
        case Z_ERRNO:
            if (ferror(stdin))
                fputs("error reading stdin/n", stderr);
            if (ferror(stdout))
                fputs("error writing stdout/n", stderr);
            break;
        case Z_STREAM_ERROR:
            fputs("invalid compression level/n", stderr);
            break;
        case Z_DATA_ERROR:
            fputs("invalid or incomplete deflate data/n", stderr);
            break;
        case Z_MEM_ERROR:
            fputs("out of memory/n", stderr);
            break;
        case Z_VERSION_ERROR:
            fputs("zlib version mismatch!/n", stderr);
        }
    }
    
    int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
    {
     int nRetCode = 0;
    
     // initialize MFC and print and error on failure
     if (!AfxWinInit(::GetModuleHandle(NULL), NULL, ::GetCommandLine(), 0))
     {
      // TODO: change error code to suit your needs
      _tprintf(_T("Fatal Error: MFC initialization failed/n"));
      nRetCode = 1;
     }
     else
     {
      // TODO: code your application's behavior here.
     }
     int ret;
     SET_BINARY_MODE(stdin);
     SET_BINARY_MODE(stdout);
    
     if (argc == 1)
     {
      ret = def(stdin,stdout,Z_DEFAULT_COMPRESSION);
      if (ret != Z_OK)
       zerr(ret);
      return ret;
     }else if (argc == 2 && strcmp(argv[1],"-d") == 0)
     {
      ret = inf(stdin,stdout);
      if (ret != Z_OK)
       zerr(ret);
      return ret;
     }else
     {
           fputs("zpipe usage: zpipe [-d] < source > dest/n", stderr);
     }
     return nRetCode;
    }

转帖：http://blog.163.com/cp7618@yeah/blog/static/702347772011114103910635/