Painful C++ string conversion

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Why the conversion between C++ string/wstring/u8string/u16string/u32string so painful?

Usage

You can convert strings through the following API:

• ext::convert<std::string>
• ext::convert<std::u8string>
• ext::convert<std::u16string>
• ext::convert<std::u32string>
• ext::convert<std::wstring>

#include <iostream>
#include <ext/convert.hpp>

using std::string_view_literals::operator""sv;

int main() {
  std::cout << ext::convert<std::string>(U"Hello world!"sv) << std::endl;
  return 0;
}

You can customize namespace and function name:

#include <iostream>
#define PAINFUL_CPP_STRING_CONVERSION_NAMESPACE utf
#define PAINFUL_CPP_STRING_CONVERSION_FUNCTION  as
#include <ext/convert.hpp>

using std::string_view_literals::operator""sv;

int main() {
  std::cout << utf::as<std::string>(U"Hello world!"sv) << std::endl;
  return 0;
}

Conversion matrix

	std::string	std::u8string	std::u16string	std::u32string	std::wstring
std::string		⚠️	⚠️	⚠️	⚠️
std::u8string	⚠️		✅	✅	✅
std::u16string	⚠️	✅		✅	✅
std::u32string	⚠️	✅	✅		✅
std::wstring	⚠️	✅	✅	✅

	std::string_view	std::u8string_view
std::string_view		⚠️
std::u8string_view	⚠️

• ✅ OK.
• ⚠️ Assuming that std::string always stores text in UTF-8 encoding.
• std::wstring can be considered as std::u16string on Windows.

TODO

• Supports span or span-like types as parameter
• Supports simdutf as a high-speed conversion implementation