C++ implements the mutual conversion of utf strings and gbk strings

This function does not seem to be implemented in standard C++ language itself, and requires the use of third-party libraries or operating system APIs. I have to complain that such an important function cannot be implemented by relying on the C++ language itself. The C++ Standards Committee is really irrelevant. Then let’s not talk nonsense, just give the implementation under Windows.

std::string Utf8ToGbk(const std::string& utf8Str) {
  // Step 1: Convert UTF-8 to Wide Char (UTF-16)
  int wideCharLen =
      MultiByteToWideChar(CP_UTF8, 0, utf8Str.c_str(), -1, nullptr, 0);
  if (wideCharLen == 0) {
    throw std::runtime_error("Failed to convert from UTF-8 to wide char.");
  }

  std::wstring wideStr(wideCharLen, 0);
  MultiByteToWideChar(CP_UTF8, 0, utf8Str.c_str(), -1, &wideStr[0],
                      wideCharLen);

  // Step 2: Convert Wide Char (UTF-16) to GBK
  int gbkLen = WideCharToMultiByte(CP_ACP, 0, wideStr.c_str(), -1, nullptr, 0,
                                   nullptr, nullptr);
  if (gbkLen == 0) {
    throw std::runtime_error("Failed to convert from wide char to GBK.");
  }

  std::string gbkStr(gbkLen, 0);
  WideCharToMultiByte(CP_ACP, 0, wideStr.c_str(), -1, &gbkStr[0], gbkLen,
                      nullptr, nullptr);

  // Remove the null terminator added by the conversion functions
  gbkStr.pop_back();

  return gbkStr;
}

std::string GbkToUtf8(const std::string& gbkStr) {
  // Step 1: Convert GBK to Wide Char (UTF-16)
  int wideCharLen =
      MultiByteToWideChar(CP_ACP, 0, gbkStr.c_str(), -1, nullptr, 0);
  if (wideCharLen == 0) {
    throw std::runtime_error("Failed to convert from GBK to wide char.");
  }

  std::wstring wideStr(wideCharLen, 0);
  MultiByteToWideChar(CP_ACP, 0, gbkStr.c_str(), -1, &wideStr[0], wideCharLen);

  // Step 2: Convert Wide Char (UTF-16) to UTF-8
  int utf8Len = WideCharToMultiByte(CP_UTF8, 0, wideStr.c_str(), -1, nullptr, 0,
                                    nullptr, nullptr);
  if (utf8Len == 0) {
    throw std::runtime_error("Failed to convert from wide char to UTF-8.");
  }

  std::string utf8Str(utf8Len, 0);
  WideCharToMultiByte(CP_UTF8, 0, wideStr.c_str(), -1, &utf8Str[0], utf8Len,
                      nullptr, nullptr);

  // Remove the null terminator added by the conversion functions
  utf8Str.pop_back();

  return utf8Str;
}
</code>

The principle of this code is very simple:

CP_ACP means local encoding, which is the default encoding defined by the operating system, and depends on the language and region settings of the current operating system. In a Chinese environment, it is the Chinese encoding of the GBk series, such as GB2312, GBK or GB18030.
A wide byte string is required to be redirected. Under Windows, std::wstring is a 16-byte string, encoded using UTF-16. This is a bit similar to the string of C# and the string of Java, both of which are UTF-16 encoding.
MultiByteToWideChar and WideCharToMultiByte are both C interfaces of the operating system. The input and returned strings are both '\0', so going to the string of c++ requires removing the last '\0' character. This needs attention.

Tested the use case without any problem. Test Utf8ToGbk:

// string utfStr = u8"This is a Chinese string for testing, check it out";  // string utfStr = u8 "test";  string utfStr = u8"abcdefg";

  string gbkStr = Utf8ToGbk(utfStr);

  // cout &lt;&lt; gbkStr &lt;&lt; "-------" &lt;&lt; endl;
  // cout &lt;&lt; () &lt;&lt; endl;
  // cout &lt;&lt; gbkStr.c_str() &lt;&lt; endl;
  // cout &lt;&lt; strlen(gbkStr.c_str()) &lt;&lt; endl;
&lt;/code&gt;

Test GbkToUtf8:

#ifdef _WIN32
  SetConsoleOutputCP(65001);
#endif

  // string gbkStr = "test";  string gbkStr = "This is a Chinese string for testing, check it out";
  // string gbkStr = "abcdefg";
  cout &lt;&lt; () &lt;&lt; endl;

  string utfStr = GbkToUtf8(gbkStr);

  cout &lt;&lt; utfStr &lt;&lt; endl;
  cout &lt;&lt; () &lt;&lt; endl;

The above is the implementation of Windows. The Linux environment needs to use other methods, such as using the iconv library.

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