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Archive for December 4th, 2018

UTF-8 support for single byte character sets is beta in Windows and likely breaks a lot of applications not expecting this (via Unicode in Microsoft Windows: UTF-8 – Wikipedia)

Posted by jpluimers on 2018/12/04

Uh-oh: [WayBack] Unicode in Microsoft Windows: UTF-8 – Wikipedia:

Microsoft Windows has a code page designated for UTF-8, code page 65001. Prior to Windows 10 insider build 17035 (November 2017),[7] it was impossible to set the locale code page to 65001, leaving this code page only available for:

  • Explicit conversion functions such as MultiByteToWideChar
  • The¬†Win32 console¬†command¬†chcp 65001¬†to translate stdin/out between UTF-8 and UTF-16.

This means that “narrow” functions, in particular¬†fopen, cannot be called with UTF-8 strings, and in fact there is no way to open all possible files using¬†fopen¬†no matter what the locale is set to and/or what bytes are put in the string, as none of the available locales can produce all possible UTF-16 characters.

On all modern non-Windows platforms, the string passed to¬†fopen¬†is effectively UTF-8. This produces an incompatibility between other platforms and Windows. The normal work-around is to add Windows-specific code to convert UTF-8 to UTF-16 using¬†MultiByteToWideChar¬†and call the “wide” function.[8]¬†Conversion is also needed even for Windows-specific api such as¬†SetWindowText¬†since many applications inherently have to use UTF-8 due to its use in file formats,¬†internet protocols, and its ability to interoperate with raw arrays of bytes.

There were proposals to add new API to portable libraries such as¬†Boost¬†to do the necessary conversion, by adding new functions for opening and renaming files. These functions would pass filenames through unchanged on Unix, but translate them to UTF-16 on Windows.[9]¬†This would allow code to be “portable”, but required just as many code changes as calling the wide functions.

With insider build 17035 and the April 2018 update (nominal build 17134) for Windows 10, a “Beta: Use Unicode UTF-8 for worldwide language support” checkbox appeared for setting the locale code page to UTF-8.[a]¬†This allows for calling “narrow” functions, including¬†fopen¬†and¬†SetWindowTextA, with UTF-8 strings. Microsoft claims this option might break¬†some¬†functions (a¬†possible¬†example is¬†_mbsrev[10]) as they were written to assume multibyte encodings used no more than 2 bytes per character, thus until now code pages with more bytes such as¬†GB 18030¬†(cp54936) and¬†UTF-8¬†could not be set as the locale.[11]


  1. Jump up^¬†[WayBack]¬†“UTF-8 in Windows”.¬†Stack Overflow. Retrieved¬†July 1,¬†2011.
  2. Jump up^¬†[WayBack]¬†“Boost.Nowide”.
  3. Jump up^ [WayBack] https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strrev-wcsrev-mbsrev-mbsrev-l
  4. Jump up^¬†[WayBack]¬†“Code Page Identifiers (Windows)”.¬†msdn.microsoft.com.

Via¬†[WayBack] Microsoft Windows Beta UTF-8 support for Ansi API could break things. Wiki Article of the Change… – Tommi Prami – Google+

Related, as handling encoding is hard, especially if it is changed or not your default:

–jeroen

Posted in .NET, C, C++, Delphi, Development, Power User, Software Development, Windows, Windows 10 | 2 Comments »

 
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