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[Zlib]_[初級]_[使用zlib庫壓縮和解壓字串STL string]

場景

1.一般在使用文字json傳輸資料, 資料量特別大時,傳輸的過程就特別耗時, 因為頻寬或者socket的快取是有限制的, 資料量越大, 傳輸時間就越長. 網站一般使用gzip來壓縮成二進位制.

說明

1.zlib庫可以實現gzip和zip方式的壓縮, 這裡只介紹zip方式的二進位制壓縮, 壓縮比還是比較可觀的, 一般寫客戶端程式已足夠.

2.修改了一下zpipe.c的實現, 其實就是把讀檔案改為讀字串, 寫檔案改為寫字串即可.

例子


// test_zlib.cpp : 定義控制檯應用程式的入口點。
//

#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; }

輸出:

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

參考