如何使用Zstd压缩C++字符串？
如何使用Zstd压缩C++字符串？
提问于 2019-09-01 18:17:19
我对C++非常陌生，我想通过Zstd压缩库压缩一个std:string对象，但到目前为止，我还没有找到用于此目的的C++示例代码。我找到了示例C代码，但似乎它们使用的是C风格的字符数组，而不是std:string对象。
示例C代码：https://github.com/facebook/zstd/blob/dev/examples/simple_compression.c
/*
* Copyright (c) 2016-present, Yann Collet, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under both the BSD-style license (found in the
* LICENSE file in the root directory of this source tree) and the GPLv2 (found
* in the COPYING file in the root directory of this source tree).
* You may select, at your option, one of the above-listed licenses.
*/
#include <stdio.h> // printf
#include <stdlib.h> // free
#include <string.h> // strlen, strcat, memset
#include <zstd.h> // presumes zstd library is installed
#include "common.h" // Helper functions, CHECK(), and CHECK_ZSTD()
static void compress_orDie(const char* fname, const char* oname)
{
size_t fSize;
void* const fBuff = mallocAndLoadFile_orDie(fname, &fSize);
size_t const cBuffSize = ZSTD_compressBound(fSize);
void* const cBuff = malloc_orDie(cBuffSize);
/* Compress.
* If you are doing many compressions, you may want to reuse the context.
* See the multiple_simple_compression.c example.
*/
size_t const cSize = ZSTD_compress(cBuff, cBuffSize, fBuff, fSize, 1);
CHECK_ZSTD(cSize);
saveFile_orDie(oname, cBuff, cSize);
/* success */
printf("%25s : %6u -> %7u - %s \n", fname, (unsigned)fSize, (unsigned)cSize, oname);
free(fBuff);
free(cBuff);
}
static char* createOutFilename_orDie(const char* filename)
{
size_t const inL = strlen(filename);
size_t const outL = inL + 5;
void* const outSpace = malloc_orDie(outL);
memset(outSpace, 0, outL);
strcat(outSpace, filename);
strcat(outSpace, ".zst");
return (char*)outSpace;
}
int main(int argc, const char** argv)
{
const char* const exeName = argv[0];
if (argc!=2) {
printf("wrong arguments\n");
printf("usage:\n");
printf("%s FILE\n", exeName);
return 1;
}
const char* const inFilename = argv[1];
char* const outFilename = createOutFilename_orDie(inFilename);
compress_orDie(inFilename, outFilename);
free(outFilename);
return 0;
}我的问题是，是否有人可以给我一个示例代码/片段，展示如何使用Zstd压缩C++字符串？
回答 4
Stack Overflow用户
发布于 2019-09-03 20:10:29
在我看来，最新版本的Boost library (version 1.70.0)在其iostreams子模块中添加了通过Zstd支持压缩。我可以管理以下C++代码片段，但似乎旧版本的Boost不支持Zstd压缩(我在Debian 10上使用的是Boost 1.67.0，它不支持Zstd )。
我现在能够组装的代码是这样的(它基于here中的代码)：
#include <iostream>
#include <algorithm>
#include <string>
#include <sstream>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/zstd.hpp>
std::string compress(std::string& data)
{
namespace bio = boost::iostreams;
std::stringstream compressed;
std::stringstream origin(data);
bio::filtering_streambuf<bio::input> out;
out.push(bio::zstd_compressor(bio::zstd_params(bio::zstd::default_compression)));
out.push(origin);
bio::copy(out, compressed);
return compressed.str();
}Stack Overflow用户
发布于 2019-09-01 18:25:56
使用string::c_str()，您可以获得一个指向一个数组的指针，该数组包含一个以null结尾的字符序列(一个C字符串)，表示string对象的当前值。
Stack Overflow用户
发布于 2020-12-21 15:57:46
namespace util {
int Util::CompressString(const string& src, string& dst, int compressionlevel) {
size_t const cBuffSize = ZSTD_compressBound(src.size());
dst.resize(cBuffSize);
auto dstp = const_cast<void*>(static_cast<const void*>(dst.c_str()));
auto srcp = static_cast<const void*>(src.c_str());
size_t const cSize = ZSTD_compress(dstp, cBuffSize, srcp, src.size(), compressionlevel);
auto code = ZSTD_isError(cSize);
if (code) {
return code;
}
dst.resize(cSize);
return code;
}
int Util::DecompressString(const string& src, string& dst) {
size_t const cBuffSize = ZSTD_getFrameContentSize(src.c_str(), src.size());
if (0 == cBuffSize) {
return cBuffSize;
}
if (ZSTD_CONTENTSIZE_UNKNOWN == cBuffSize) {
return StreamDecompressString(src, dst);
}
if (ZSTD_CONTENTSIZE_ERROR == cBuffSize) {
return -2;
}
dst.resize(cBuffSize);
auto dstp = const_cast<void*>(static_cast<const void*>(dst.c_str()));
auto srcp = static_cast<const void*>(src.c_str());
size_t const cSize = ZSTD_decompress(dstp, cBuffSize, srcp, src.size());
auto code = ZSTD_isError(cSize);
if (code) {
return code;
}
dst.resize(cSize);
return code;
}
int Util::StreamCompressString(const string& src, string& dst, int compressionlevel) {
size_t const buffInSize = ZSTD_CStreamInSize();
string buffInTmp;
buffInTmp.reserve(buffInSize);
auto buffIn = const_cast<void*>(static_cast<const void*>(buffInTmp.c_str()));
auto buffOutSize = ZSTD_CStreamOutSize();
string buffOutTmp;
buffOutTmp.reserve(buffOutSize);
auto buffOut = const_cast<void*>(static_cast<const void*>(buffOutTmp.c_str()));
ZSTD_CCtx* const cctx = ZSTD_createCCtx();
ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, compressionlevel);
size_t const toRead = buffInSize;
auto local_pos = 0;
auto buff_tmp = const_cast<char*>(buffInTmp.c_str());
for (;;) {
size_t read = src.copy(buff_tmp, toRead, local_pos);
local_pos += read;
int const lastChunk = (read < toRead);
ZSTD_EndDirective const mode = lastChunk ? ZSTD_e_end : ZSTD_e_continue;
ZSTD_inBuffer input = {buffIn, read, 0};
int finished;
do {
ZSTD_outBuffer output = {buffOut, buffOutSize, 0};
size_t const remaining = ZSTD_compressStream2(cctx, &output, &input, mode);
dst.insert(dst.end(), buffOutTmp.begin(), buffOutTmp.begin() + output.pos);
finished = lastChunk ? (remaining == 0) : (input.pos == input.size);
} while (!finished);
if (lastChunk) {
break;
}
}
ZSTD_freeCCtx(cctx);
return 0;
}
int Util::StreamDecompressString(const string& src, string& dst, int compressionlevel) {
size_t const buffInSize = ZSTD_DStreamInSize();
string buffInTmp;
buffInTmp.reserve(buffInSize);
auto buffIn = const_cast<void*>(static_cast<const void*>(buffInTmp.c_str()));
auto buffOutSize = ZSTD_DStreamOutSize();
string buffOutTmp;
buffOutTmp.reserve(buffOutSize);
auto buffOut = const_cast<void*>(static_cast<const void*>(buffOutTmp.c_str()));
ZSTD_DCtx* const dctx = ZSTD_createDCtx();
size_t const toRead = buffInSize;
size_t read;
size_t last_ret = 0;
size_t local_pos = 0;
auto buff_tmp = const_cast<char*>(buffInTmp.c_str());
while ((read = src.copy(buff_tmp, toRead, local_pos))) {
local_pos += read;
ZSTD_inBuffer input = {buffIn, read, 0};
while (input.pos < input.size) {
ZSTD_outBuffer output = {buffOut, buffOutSize, 0};
size_t const ret = ZSTD_decompressStream(dctx, &output, &input);
dst.insert(dst.end(), buffOutTmp.begin(), buffOutTmp.begin() + output.pos);
last_ret = ret;
}
}
ZSTD_freeDCtx(dctx);
if(last_ret != 0) {
return -3;
}
return 0;
}
} // namespace util页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/57745122
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