c++ - 无法使用 sqlite3 和 C++ 解压缩从 sql 表中选择的压缩字符串

Question

描述

我正在尝试将压缩数据插入到 sql 表中，然后提取并解压缩它。起初我压缩一个字符串，然后将它插入到一个表中(第 1 节)。压缩工作正常。即使当我在插入之前尝试解压缩它时，我也会取回字符串。问题出现在插入字符串并稍后尝试将其提取回来之后。

正如您在代码的第 2 部分中看到的那样。解压就不行了。我不知道为什么我从表中提取它后它不再起作用。

---

源代码

#include <zlc/zlibcomplete.hpp>
#include <string>
#include "3rdparty/sqlite_modern_cpp.h"

using namespace std;
using namespace zlibcomplete;

int main()
{
   //SECTION 1
   database db("data.db");
   db << "CREATE TABLE IF NOT EXISTS paragraph(ID INTEGER PRIMARY KEY, LINE TEXT);";
   string line = "hello world!";
   //Compress string by using zlib
   GZipCompressor compressor(9, auto_flush);
   string compressed_line = compressor.compress(line);
   compressor.finish();
   
   //IF I DECOMPRESS STRING HERE IT WORKS FINE!!!
   GZipDecompressor decompressor;
   string output = decompressor.decompress(line);
  
   //insert compressed string into table paragraph
   db <<"insert into paragraph(ID,LINE) VALUES (?,?);"
      << 1
      << compressed_line;


  //SECTION 2: Problem starts here where I try to return the compressed value
   db <<"select line from paragraph where id = ?;"
      << "1"
      >>[&](string line)
      {
        //Decompress string by using zlib
        GZipDecompressor decompressor;
        string output = decompressor.decompress(line);
        //out is empty I don't know why???
        cout << output  << endl;
      }; 
   return 0;
}

---

修正后更新

第一次下载base64 solution 中指出的类.

#include <zlc/zlibcomplete.hpp>
#include <string>
#include "3rdparty/sqlite_modern_cpp.h"
#include "base64.h"

using namespace std;
using namespace zlibcomplete;

int main()
{
   //SECTION 1
   database db("data.db");
   db << "CREATE TABLE IF NOT EXISTS paragraph(ID INTEGER PRIMARY KEY, LINE TEXT);";
   string line = "hello world!";
   //Compress string by using zlib
   GZipCompressor compressor(9, auto_flush);
   string compressed_line = compressor.compress(line);
   compressor.finish();
  std::string compressed = base64_encode(reinterpret_cast<const unsigned char*>(compressed_line.c_str()), compressed_line.length());
  
   //insert compressed string into table paragraph
   db <<"insert into paragraph(ID,LINE) VALUES (?,?);"
      << 1
      << compressed;


   db <<"select line from paragraph where id = ?;"
      << "1"
      >>[&](string line)
      {
        //decode HERE
        std::string compressed_decoded = base64_decode(line);
        //Decompress string by using zlib
        GZipDecompressor decompressor;
        string output = decompressor.decompress(line);
        cout << output  << endl;
      }; 
   return 0;
}

Answer 1

您的代码无法处理压缩字符串中的零。如果压缩字符串中有一个字符 0，那么文本将被截断并且无法再进行反向操作。