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
// 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:
========= CompressString ===========Source Buffer Size: 662Compress 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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