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zlib库压缩和解压字符串STL string的实例详解

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zlib库压缩和解压字符串STL string的实例详解 。

场景 。

1.一般在使用文本json传输数据, 数据量特别大时,传输的过程就特别耗时, 因为带宽或者socket的缓存是有限制的, 数据量越大, 传输时间就越长. 网站一般使用gzip来压缩成二进制. 。

说明 。

1.zlib库可以实现gzip和zip方式的压缩, 这里只介绍zip方式的二进制压缩, 压缩比还是比较可观的, 一般写客户端程序已足够. 。

2.修改了一下zpipe.c的实现, 其实就是把读文件改为读字符串, 写文件改为写字符串即可. 。

例子 。

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// test_zlib.cpp : 定义控制台应用程序的入口点。
//
 
#include "stdafx.h"
 
#include <string>
#include <iostream>
#include <memory>
#include <assert.h>
#include "zlib.h"
 
 
 
// E:\software\Lib\compress\zlib-1.2.5\src\examples
// zpipe.c
 
#define CHUNK 16384
 
/* Compress from file source to file dest until EOF on source.
   def() returns Z_OK on success, Z_MEM_ERROR if memory could not be
   allocated for processing, Z_STREAM_ERROR if an invalid compression
   level is supplied, Z_VERSION_ERROR if the version of zlib.h and the
   version of the library linked do not match, or Z_ERRNO if there is
   an error reading or writing the files. */
int CompressString( const char * in_str, size_t in_len,
   std::string& out_str, int level)
{
   if (!in_str)
     return Z_DATA_ERROR;
 
   int ret, flush;
   unsigned have;
   z_stream strm;
 
   unsigned char out[CHUNK];
 
   /* allocate deflate state */
   strm.zalloc = Z_NULL;
   strm.zfree = Z_NULL;
   strm.opaque = Z_NULL;
   ret = deflateInit(&strm, level);
   if (ret != Z_OK)
     return ret;
 
   std::shared_ptr<z_stream> sp_strm(&strm,[](z_stream* strm){
      ( void )deflateEnd(strm);
   });
   const char * end = in_str+in_len;
 
   size_t pos_index = 0;
   size_t distance = 0;
   /* compress until end of file */
   do {
     distance = end - in_str;
     strm.avail_in = (distance>=CHUNK)?CHUNK:distance;
     strm.next_in = (Bytef*)in_str;
 
     // next pos
     in_str+= strm.avail_in;
     flush = (in_str == end) ? Z_FINISH : Z_NO_FLUSH;
 
     /* run deflate() on input until output buffer not full, finish
       compression if all of source has been read in */
     do {
       strm.avail_out = CHUNK;
       strm.next_out = out;
       ret = deflate(&strm, flush);  /* no bad return value */
       if (ret == Z_STREAM_ERROR)
         break ;
       have = CHUNK - strm.avail_out;
       out_str.append(( const char *)out,have);
     } while (strm.avail_out == 0);
     if (strm.avail_in != 0);   /* all input will be used */
       break ;
 
     /* done when last data in file processed */
   } while (flush != Z_FINISH);
   if (ret != Z_STREAM_END) /* stream will be complete */
     return Z_STREAM_ERROR;
 
   /* clean up and return */
   return Z_OK;
}
 
/* Decompress from file source to file dest until stream ends or EOF.
   inf() returns Z_OK on success, Z_MEM_ERROR if memory could not be
   allocated for processing, Z_DATA_ERROR if the deflate data is
   invalid or incomplete, Z_VERSION_ERROR if the version of zlib.h and
   the version of the library linked do not match, or Z_ERRNO if there
   is an error reading or writing the files. */
int DecompressString( const char * in_str, size_t in_len, std::string& out_str)
{
   if (!in_str)
     return Z_DATA_ERROR;
 
   int ret;
   unsigned have;
   z_stream strm;
   unsigned char out[CHUNK];
 
   /* allocate inflate state */
   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;
 
   std::shared_ptr<z_stream> sp_strm(&strm,[](z_stream* strm){
      ( void )inflateEnd(strm);
   });
 
   const char * end = in_str+in_len;
 
   size_t pos_index = 0;
   size_t distance = 0;
 
   int flush = 0;
   /* decompress until deflate stream ends or end of file */
   do {
     distance = end - in_str;
     strm.avail_in = (distance>=CHUNK)?CHUNK:distance;
     strm.next_in = (Bytef*)in_str;
 
     // next pos
     in_str+= strm.avail_in;
     flush = (in_str == end) ? Z_FINISH : Z_NO_FLUSH;
 
     /* run inflate() on input until output buffer not full */
     do {
       strm.avail_out = CHUNK;
       strm.next_out = out;
       ret = inflate(&strm, Z_NO_FLUSH);
       if (ret == Z_STREAM_ERROR) /* state not clobbered */
         break ;
       switch (ret) {
       case Z_NEED_DICT:
         ret = Z_DATA_ERROR;   /* and fall through */
       case Z_DATA_ERROR:
       case Z_MEM_ERROR:
         return ret;
       }
       have = CHUNK - strm.avail_out;
       out_str.append(( const char *)out,have);
     } while (strm.avail_out == 0);
 
     /* done when inflate() says it's done */
   } while (flush != Z_FINISH);
 
   /* clean up and return */
   return ret == Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
}
 
 
int _tmain( int argc, _TCHAR* argv[])
{
   const char * buf = "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "01010101010101010101010000000000000000000000000000011111111111111"
     "qwertyuiop[]" ;
 
   std::cout << "========= CompressString ===========" << std::endl;
   std::cout << "Source Buffer Size: " << strlen (buf) << std::endl;
   std::string out_compress;
   assert (CompressString(buf, strlen (buf),out_compress,Z_DEFAULT_COMPRESSION) == Z_OK);
   std::cout << "Compress Buffer Size: " << out_compress.size() << std::endl;
 
   std::cout << "========= DecompressString ===========" << std::endl;
   std::string out_decompress;
   assert (DecompressString(out_compress.c_str(),out_compress.size(),out_decompress) == Z_OK);
   std::cout << "Decompress Buffer Size: " << out_decompress.size() << std::endl;
   assert (!out_decompress.compare(buf));
 
   return 0;
}

输出

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========= CompressString ===========
Source Buffer Size: 662
Compress Buffer Size: 38
========= DecompressString ===========
Decompress Buffer Size: 662

参考 。

zlib\src\examples\zpipe.c 。

C++ Code Snippet - Compressing STL Strings with zlib 。

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原文链接：http://blog.csdn.net/infoworld/article/details/55101712 。

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