How to convert from UTF-8 to ANSI using standard c++

Question

I have some strings read from the database, stored in a char* and in UTF-8 format (you know, \"á\" is encoded as 0xC3 0xA1). But, in order to write them to a file, I first n

Answer 1

This should work:

#include 
#include 

using namespace std::string_literals;

std::string to_utf8(const std::string& str, const std::locale& loc = std::locale{}) {
  using wcvt = std::wstring_convert, char32_t>;
  std::u32string wstr(str.size(), U'\0');
  std::use_facet>(loc).widen(str.data(), str.data() + str.size(), &wstr[0]);
  return wcvt{}.to_bytes(wstr.data(),wstr.data() + wstr.size());
}

std::string from_utf8(const std::string& str, const std::locale& loc = std::locale{}) {
  using wcvt = std::wstring_convert, char32_t>;
  auto wstr = wcvt{}.from_bytes(str);
  std::string result(wstr.size(), '0');
  std::use_facet>(loc).narrow(wstr.data(), wstr.data() + wstr.size(), '?', &result[0]);
  return result;
}

int main() {
  auto s0 = u8"Blöde C++ Scheiße äöü!!1Elf"s;
  auto s1 = from_utf8(s0);
  auto s2 = to_utf8(s1);

  return 0;
}

For VC++:

#include 
#include 

using namespace std::string_literals;

std::string to_utf8(const std::string& str, const std::locale& loc = std::locale{}) {
  using wcvt = std::wstring_convert, int32_t>;
  std::u32string wstr(str.size(), U'\0');
  std::use_facet>(loc).widen(str.data(), str.data() + str.size(), &wstr[0]);
  return wcvt{}.to_bytes(
    reinterpret_cast(wstr.data()),
    reinterpret_cast(wstr.data() + wstr.size())
  );
}

std::string from_utf8(const std::string& str, const std::locale& loc = std::locale{}) {
  using wcvt = std::wstring_convert, int32_t>;
  auto wstr = wcvt{}.from_bytes(str);
  std::string result(wstr.size(), '0');
  std::use_facet>(loc).narrow(
    reinterpret_cast(wstr.data()),
    reinterpret_cast(wstr.data() + wstr.size()),
    '?', &result[0]);
  return result;
}

int main() {
  auto s0 = u8"Blöde C++ Scheiße äöü!!1Elf"s;
  auto s1 = from_utf8(s0);
  auto s2 = to_utf8(s1);

  return 0;
}