字符串到 UTF-8 在 C++ 中的转换

Question

I have a string Test\xc2\xae represented in Hex as 0x54 0x65 0x73 0x74 0x5c 0x78 0x63 0x32 0x5c 0x78 0x61 0x65 . The character set \xc2\xae in this string is nothing but the UTF-8 Encoding of ® (registered trademark).

I want to write a c++ function which can convert \xc2 (in Hex 0x5c 0x78 0x63 0x32 ) character set to hex value 0xc2 .

eg I want to write a c++ function which can convert Test\xc2\xae [ 0x54 0x65 0x73 0x74 0x5c 0x78 0x63 0x32 0x5c 0x78 0x61 0x65 ] to Test® [ 0x54 0x65 0x73 0x74 0xc2 0xae ]

Answer 1

As far as I understand your question, I think that you try to convert each \x?? sequence (four chars), where ?? is a sequence of two hexadecimal digits, to a unique char with the value which was expressed in hexadecimal.

If you don't have to use huge libraries dedicated to this, maybe this trivial algorithm could do the trick.

/**
  g++ -std=c++17 -o prog_cpp prog_cpp.cpp \
      -pedantic -Wall -Wextra -Wconversion -Wno-sign-conversion \
      -g -O0 -UNDEBUG -fsanitize=address,undefined
**/

#include <iostream>
#include <string>
#include <cctype>

std::string
convert_backslash_x(const std::string &str)
{
  auto result=std::string{};
  for(auto start=std::string::size_type{0};;)
  {
    const auto pos=str.find("\\x", start);
    if((pos==str.npos)||  // not found
       (pos+4>size(str))) // too near from the end
    {
      // keep the remaining of the string
      result.append(str, start);
      break;
    }
    // keep everything until this position
    result.append(str, start, pos-start);
    const auto c1=std::tolower(str[pos+2]), c2=std::tolower(str[pos+3]);
    if(std::isxdigit(c1)&&std::isxdigit(c2))
    {
      // convert two hex digits to a char with this value
      const auto h1=std::isalpha(c1) ? 10+(c1-'a') : (c1-'0');
      const auto h2=std::isalpha(c2) ? 10+(c2-'a') : (c2-'0');
      result+=char(h1*16+h2);
      // go on after this \x?? sequence
      start=pos+4; 
    }
    else
    {
      // keep this incomplete \x sequence as is
      result+="\\x";
      // go on after this \x sequence
      start=pos+2;
    }
  }
  return result;
}

int
main()
{
  for(const auto &s: {"Test\\xc2\\xae",
                      "Test\\xc2\\xae Test\\xc2\\xae",
                      "Test\\xc2\\xa",
                      "Test\\x\\xc2\\xa"})
  {
    std::cout << '(' << s << ") --> (" << convert_backslash_x(s) << ")\n";
  }
  return 0;
}