fork download
copy 
  1. #include <cassert>
  2. #include <cwctype>
  3. #include <cstdlib>
  4. #include <iomanip>
  5. #include <iostream>
  6. #include <locale>
  7. #include <string>
  8.  
  9. using std::size_t;
  10.  
  11. std::u16string make_u16string( const std::wstring& ws )
  12. /* Creates a UTF-16 string from a wide-character string.  Any wide characters
  13.  * outside the allowed range of UTF-16 are mapped to the sentinel value U+FFFD,
  14.  * per the Unicode documentation. (http://w...content-available-to-author-only...e.org/faq/private_use.html
  15.  * retrieved 12 March 2017.) Unpaired surrogates in ws are also converted to
  16.  * sentinel values.  Noncharacters, however, are left intact.  As a fallback,
  17.  * if wide characters are the same size as char16_t, this does a more trivial
  18.  * construction using that implicit conversion.
  19.  */
  20. {
  21.   /* We assume that, if this test passes, a wide-character string is already
  22.    * UTF-16, or at least converts to it implicitly without needing surrogate
  23.    * pairs.
  24.    */
  25.   if ( sizeof(wchar_t) == sizeof(char16_t) ) {
  26.     return std::u16string( ws.begin(), ws.end() );
  27.   } else {
  28.     /* The conversion from UTF-32 to UTF-16 might possibly require surrogates.
  29.      * A surrogate pair suffices to represent all wide characters, because all
  30.      * characters outside the range will be mapped to the sentinel value
  31.      * U+FFFD.  Add one character for the terminating NUL.
  32.      */
  33.     const size_t max_len = 2 * ws.length() + 1;
  34.     // Our temporary UTF-16 string.
  35.     std::u16string result;
  36.  
  37.     result.reserve(max_len);
  38.  
  39.     for ( const wchar_t& wc : ws ) {
  40.       const std::wint_t chr = wc;
  41.  
  42.       if ( chr < 0 || chr > 0x10FFFF || (chr >= 0xD800 && chr <= 0xDFFF) ) {
  43.         // Invalid code point.  Replace with sentinel, per Unicode standard:
  44.         constexpr char16_t sentinel = u'\uFFFD';
  45.         result.push_back(sentinel);
  46.       } else if ( chr < 0x10000UL ) { // In the BMP.
  47.         result.push_back(static_cast<char16_t>(wc));
  48.       } else {
  49.         assert( chr <= 0x10FFFFUL ); // Quick and dirty error-checking.
  50.         const char16_t leading = static_cast<char16_t>( 
  51.           ((chr-0x10000UL) / 0x400U) + 0xD800U );
  52.         const char16_t trailing = static_cast<char16_t>( 
  53.           ((chr-0x10000UL) % 0x400U) + 0xDC00U );
  54.  
  55.         result.append({leading, trailing});
  56.       } // end if
  57.     } // end for
  58.  
  59.    /* The returned string is shrunken to fit, which might not be the Right
  60.     * Thing if there is more to be added to the string.
  61.     */
  62.     result.shrink_to_fit();
  63.  
  64.     // We depend here on the compiler to optimize the move constructor.
  65.     return result;
  66.   } // end if
  67.   // Not reached.
  68. }
  69.  
  70. int main(void)
  71. {
  72.   static const std::wstring wtest(L"☪☮∈✡℩☯✝ \U0001F644");
  73.   static const std::u16string u16test(u"☪☮∈✡℩☯✝ \U0001F644");
  74.   const std::u16string converted = make_u16string(wtest);
  75.  
  76.   // The correct locale name may vary by OS, e.g., "en_US.utf8".
  77.   constexpr char locale_name[] = "";
  78.   // Some online compilers need the next line commented out:
  79.   std::locale::global(std::locale(locale_name));
  80.   std::wcout.imbue(std::locale());
  81.  
  82.   std::wcout << L"sizeof(wchar_t) == " << sizeof(wchar_t) << L".\n";
  83.  
  84.   for( size_t i = 0; i <= u16test.length(); ++i ) {
  85.     if ( u16test[i] != converted[i] ) {
  86.       std::wcout << std::hex << std::showbase
  87.                  << std::right << std::setfill(L'0')
  88.                  << std::setw(4) << (unsigned)converted[i] << L" ≠ "
  89.                  << std::setw(4) << (unsigned)u16test[i] << L" at "
  90.                  << i << L'.' << std::endl;
  91.       return EXIT_FAILURE;
  92.     } // end if
  93.   } // end for
  94.  
  95.   std::wcout << wtest << std::endl;
  96.  
  97.   return EXIT_SUCCESS;
  98. }
Success #stdin #stdout 0s 16920KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
sizeof(wchar_t) == 4.
☪☮∈✡℩☯✝ 🙄
https://ideone.com/nrCowQ
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!