zlib库压缩和解压字符串STL string的实例详解

2023-09-22 11:46:05 54

zlib库压缩和解压字符串STLstring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
#include
#include
#include
#include"zlib.h"



//E:\software\Lib\compress\zlib-1.2.5\src\examples
//zpipe.c

#defineCHUNK16384

/*CompressfromfilesourcetofiledestuntilEOFonsource.
def()returnsZ_OKonsuccess,Z_MEM_ERRORifmemorycouldnotbe
allocatedforprocessing,Z_STREAM_ERRORifaninvalidcompression
levelissupplied,Z_VERSION_ERRORiftheversionofzlib.handthe
versionofthelibrarylinkeddonotmatch,orZ_ERRNOifthereis
anerrorreadingorwritingthefiles.*/
intCompressString(constchar*in_str,size_tin_len,
std::string&out_str,intlevel)
{
if(!in_str)
returnZ_DATA_ERROR;

intret,flush;
unsignedhave;
z_streamstrm;

unsignedcharout[CHUNK];

/*allocatedeflatestate*/
strm.zalloc=Z_NULL;
strm.zfree=Z_NULL;
strm.opaque=Z_NULL;
ret=deflateInit(&strm,level);
if(ret!=Z_OK)
returnret;

std::shared_ptrsp_strm(&strm,[](z_stream*strm){
(void)deflateEnd(strm);
});
constchar*end=in_str+in_len;

size_tpos_index=0;
size_tdistance=0;
/*compressuntilendoffile*/
do{
distance=end-in_str;
strm.avail_in=(distance>=CHUNK)?CHUNK:distance;
strm.next_in=(Bytef*)in_str;

//nextpos
in_str+=strm.avail_in;
flush=(in_str==end)?Z_FINISH:Z_NO_FLUSH;

/*rundeflate()oninputuntiloutputbuffernotfull,finish
compressionifallofsourcehasbeenreadin*/
do{
strm.avail_out=CHUNK;
strm.next_out=out;
ret=deflate(&strm,flush);/*nobadreturnvalue*/
if(ret==Z_STREAM_ERROR)
break;
have=CHUNK-strm.avail_out;
out_str.append((constchar*)out,have);
}while(strm.avail_out==0);
if(strm.avail_in!=0);/*allinputwillbeused*/
break;

/*donewhenlastdatainfileprocessed*/
}while(flush!=Z_FINISH);
if(ret!=Z_STREAM_END)/*streamwillbecomplete*/
returnZ_STREAM_ERROR;

/*cleanupandreturn*/
returnZ_OK;
}

/*DecompressfromfilesourcetofiledestuntilstreamendsorEOF.
inf()returnsZ_OKonsuccess,Z_MEM_ERRORifmemorycouldnotbe
allocatedforprocessing,Z_DATA_ERRORifthedeflatedatais
invalidorincomplete,Z_VERSION_ERRORiftheversionofzlib.hand
theversionofthelibrarylinkeddonotmatch,orZ_ERRNOifthere
isanerrorreadingorwritingthefiles.*/
intDecompressString(constchar*in_str,size_tin_len,std::string&out_str)
{
if(!in_str)
returnZ_DATA_ERROR;

intret;
unsignedhave;
z_streamstrm;
unsignedcharout[CHUNK];

/*allocateinflatestate*/
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)
returnret;

std::shared_ptrsp_strm(&strm,[](z_stream*strm){
(void)inflateEnd(strm);
});

constchar*end=in_str+in_len;

size_tpos_index=0;
size_tdistance=0;

intflush=0;
/*decompressuntildeflatestreamendsorendoffile*/
do{
distance=end-in_str;
strm.avail_in=(distance>=CHUNK)?CHUNK:distance;
strm.next_in=(Bytef*)in_str;

//nextpos
in_str+=strm.avail_in;
flush=(in_str==end)?Z_FINISH:Z_NO_FLUSH;

/*runinflate()oninputuntiloutputbuffernotfull*/
do{
strm.avail_out=CHUNK;
strm.next_out=out;
ret=inflate(&strm,Z_NO_FLUSH);
if(ret==Z_STREAM_ERROR)/*statenotclobbered*/
break;
switch(ret){
caseZ_NEED_DICT:
ret=Z_DATA_ERROR;/*andfallthrough*/
caseZ_DATA_ERROR:
caseZ_MEM_ERROR:
returnret;
}
have=CHUNK-strm.avail_out;
out_str.append((constchar*)out,have);
}while(strm.avail_out==0);

/*donewheninflate()saysit'sdone*/
}while(flush!=Z_FINISH);

/*cleanupandreturn*/
returnret==Z_STREAM_END?Z_OK:Z_DATA_ERROR;
}


int_tmain(intargc,_TCHAR*argv[])
{
constchar*buf="01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"01010101010101010101010000000000000000000000000000011111111111111"
"qwertyuiop[]";

std::cout<<"=========CompressString==========="<
输出:
=========CompressString===========
SourceBufferSize:662
CompressBufferSize:38
=========DecompressString===========
DecompressBufferSize:662

参考
zlib\src\examples\zpipe.c
C++CodeSnippet-CompressingSTLStringswithzlib
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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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