Unicode in Microsoft Windows: Difference between revisions

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{{Short description|Overview on Unicode implementation in Microsoft Windows}}

{{more citations needed|date=June 2011}}

[[Microsoft]] was one of the first companies to implement [[Unicode]] in their products. [[Windows NT]] was the first operating system that used "wide characters" in [[system call]]s. Using the (now obsolete) [[UCS-2]] encoding scheme at first, it was upgraded to the [[variable-width encoding]] [[UTF-16]] starting with [[Windows 2000]], allowing a representation of additional planes with surrogate pairs. However Microsoft did not support [[UTF-8]] in its API until May 2019, though it now appears to be encouraging its use.<ref>{{cite web|title=Use UTF-8 code pages in Windows apps|url=https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page|language=en}}</ref>

Before 2019, Microsoft emphasized UTF-16 (i.e. -W API), but has since recommended to use [[UTF-8]] (at least in some cases),<ref name="Microsoft-UTF-8" /> on Windows and [[Xbox]] (and in other of its products), even states "UTF-8 is the universal code page for internationalization [and] UTF-16 [... is] a unique burden that Windows places on code that targets multiple platforms. [..] Windows [is] moving forward to support UTF-8 to remove this unique burden [resulting] in fewer internationalization issues in apps and games".<ref name="Microsoft GDK" />

A large amount of Microsoft documentation uses the word "Unicode" to refer explicitly to the UTF-16 encoding. Anything else, including UTF-8, is not "Unicode".

A large amount of Microsoft documentation uses the word "Unicode" to refer explicitly to the UTF-16 encoding. Anything else, including UTF-8, is not "Unicode" in Microsoft's outdated language (while UTF-8 and UTF-16 are both Unicode according to [[Unicode|the Unicode Standard]], or encodings/"transformation formats" thereof).

== In various Windows families ==

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Current Windows versions and all back to [[Windows XP]] and prior [[Windows NT]] (3.x, 4.0) are shipped with [[Windows API|system libraries]] that support string [[character encoding|encoding]] of two types: 16-bit "Unicode" ([[UTF-16]] since [[Windows 2000]]) and a (sometimes multibyte) encoding called the "[[Windows code page|code page]]" (or incorrectly referred to as ''[[American National Standards Institute|ANSI]] code page''). 16-bit functions have names suffixed with 'W' (from [[wide character|"wide"]]) such as <code>SetWindowTextW</code>. Code page oriented functions use the suffix 'A' for "ANSI" such as <code>SetWindowTextA</code> (some other conventions were used for APIs that were copied from other systems, such as <code>_wfopen/fopen</code> or <code>wcslen/strlen</code>). This split was necessary because many languages, including [[C (programming language)|C]], did not provide a clean way to pass both 8-bit and 16-bit strings to the same function.

[[Microsoft]] attempted to support Unicode "portably" by providing a "UNICODE" switch to the compiler, that switches unsuffixed "generic" calls from the 'A' to the 'W' interface and converts all string constants to "wide" UTF-16 versions.<ref>{{cite web|title=Unicode in the Windows API|url=https://msdn.microsoft.com/en-us/library/windows/desktop/dd374089%28v=vs.85%29.aspx|access-date=7 May 2018}}</ref><ref>{{cite web|title=Conventions for Function Prototypes (Windows)|url=https://msdn.microsoft.com/en-us/library/windows/desktop/dd317766(v=vs.85).aspx|website=MSDN|access-date=7 May 2018|language=en}}</ref> This does not actually work because it does not translate UTF-8 outside of string constants, resulting in code that attempts to open files just not compiling.{{citation needed|date=October 2019}}

Most 'A' functions are implemented as [[wrapper function|wrappers]] that translate the text using the current code page to UTF-16 and then call the corresponding 'W' functions.{{citation needed|date=June 2020}} 'A' functions that return strings do the opposite conversion, turning characters that don't exist in the current locale into '?'.

[[Microsoft]] attempted to support Unicode "portably" by providing a "UNICODE" switch to the compiler, that switches unsuffixed "generic" calls from the 'A' to the 'W' interface and converts all string constants to "wide" UTF-16 versions.<ref>{{cite web|title=Unicode in the Windows API|url=https://msdn.microsoft.com/en-us/library/windows/desktop/dd374089%28v=vs.85%29.aspx|access-date=7 May 2018}}</ref><ref>{{cite web|title=Conventions for Function Prototypes (Windows)|url=https://msdn.microsoft.com/en-us/library/windows/desktop/dd317766(v=vs.85).aspx|website=MSDN|access-date=7 May 2018|language=en}}</ref> This does not actually work because it does not translate UTF-8 outside of string constants, resulting in code that attempts to open files just not compiling.{{citation needed|date=October 2019}}

Earlier, and independent of the "UNICODE" switch, Windows also provided the Multibyte Character Sets (MBCS) API switch.<ref>{{cite web|title=Support for Multibyte Character Sets (MBCSs)|url=https://docs.microsoft.com/en-us/cpp/text/support-for-multibyte-character-sets-mbcss?view=vs-2019|access-date=2020-06-15|language=en}}</ref> This changes some functions that don't work in MBCS such as <code>strrev</code> to an MBCS-aware one such as <code>_mbsrev</code>.<ref>{{cite web|title=Double-byte Character Sets|url=https://docs.microsoft.com/en-us/windows/win32/intl/double-byte-character-sets|website=MSDN|access-date=2020-06-15|date=2018-05-31|quote=our applications use DBCS Windows code pages with the "A" versions of Windows functions.}}</ref><ref>[https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strrev-wcsrev-mbsrev-mbsrev-l _strrev, _wcsrev, _mbsrev, _mbsrev_l] Microsoft Docs</ref>

=== Windows CE ===

In (the now discontinued) [[Windows CE]], UTF-16 was used almost exclusively, with the 'A' API mostly missing.<ref>{{cite web|title=Differences Between the Windows CE and Windows NT Implementations of TAPI|url=https://msdn.microsoft.com/en-us/library/aa454022.aspx|website=MSDN|date=28 August 2006 |access-date=7 May 2018|quote=Windows CE is Unicode-based. You might have to recompile source code that was written for a Windows NT-based application.}}</ref> A limited set of ANSI API is available in Windows CE 5.0, for use on a reduced set of locales that may be selectively built onto the runtime image.<ref>{{cite web|title=Code Pages (Windows CE 5.0)|url=https://docs.microsoft.com/en-us/previous-versions/windows/embedded/ms903783(v=msdn.10)|website=Microsoft Docs| date=14 September 2012 |access-date=7 May 2018|language=en-us}}</ref>

{{expand section|date=June 2011}}

=== Windows 9x ===

{{Main article|Microsoft Layer for Unicode}}

In 2001, Microsoft released a special supplement to Microsoft's old [[Windows 9x]] systems. It includes a dynamic link library, 'unicows.dll', (only 240 &nbsp;KB) containing the 16-bit flavor (the ones with the letter W on the end) of all the basic functions of Windows API. It is merely a translation layer: <code>SetWindowTextW</code> will simply convert its input using the current codepage and call <code>SetWindowTextA</code>.

== UTF-8 ==

Microsoft Windows ([[Windows XP]] and later) has a code page designated for [[UTF-8]], code page 65001<ref>{{cite web|title=Code Page Identifiers (Windows)|url=https://msdn.microsoft.com/en-us/library/windows/desktop/dd317756(v=vs.85).aspx|website=msdn.microsoft.com| date=7 January 2021 |language=en}}</ref> or <code>CP_UTF8</code>. For a long time, it was impossible to set the locale code page to 65001, leaving this code page only available for (a) explicit conversion functions such as MultiByteToWideChar and/or (b) the [[Win32 console]] command <code>chcp 65001</code> to translate stdin/out between UTF-8 and UTF-16. This meant that "narrow" functions, in particular <code>[[C file input/output#fopen|fopen]]</code> (which opens files), couldn't be called with UTF-8 strings, and in fact there was no way to open all possible files using <code>fopen</code> no matter what the locale was set to and/or what bytes were put in the string, as none of the available locales could produce all possible UTF-16 characters. This problem also applied to all other APIs that take or return 8-bit strings, including Windows ones such as <code>SetWindowText</code>.

OnPrograms allthat modernwanted to non-Windowsuse platformsUTF-8, thein file-nameparticular stringcode passedintended to <code>fopen</code>be isportable effectivelyto UTF-8.other Thisoperating producedsystems, anneeded incompatibilitya betweenworkaround otherfor platformsthis and Windowsdeficiency. The usual work-around was to add codenew functions to open files that convert UTF-8 to UTF-16 using [[MultiByteToWideChar]] and call the "wide" function instead of <code>fopen</code>.<ref>{{cite web|url=https://stackoverflow.com/questions/166503/utf-8-in-windows|title=UTF-8 in Windows|publisher=[[Stack Overflow]]|access-date=July 1, 2011}}</ref> AnotherDozens popularof workmulti-aroundplatform waslibraries toadded convertwrapper the namefunctions to the [[8.3 filename]] equivalent,do this isconversion necessaryon ifWindows the(and <code>fopen</code>pass isUTF-8 insidethrough aunchanged libraryon functionothers), thatan takes a string filename and thus calling another functionexample is nota possible.proposed There were also proposalsaddition to add new APIs to portable libraries such as [[Boost (C++ libraries)|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. Such a library, {{tt|Boost.Nowide,}}.<ref>{{cite web|url=https://github.com/boostorg/nowide|title=Boost.Nowide|website=[[GitHub]]}}</ref> wasAnother acceptedpopular into Boost<ref>{{cite web|url=https://lists.boost.org/boostwork-announce/2017/06/0516.php|title=Boostaround mailingwas list}}</ref>to andconvert willthe bename part ofto the 1[[8.733 release.{{Needsfilename]] update|date=Marchequivalent, 2021|reason=this citesis anecessary 2017if mailingthe list<code>fopen</code> post,is hasinside ita beenlibrary. released?}}None Thisof wouldthese allowworkarounds codeare toconsidered be "portable"good, but required just as manythey coderequire changes as callingto the widecode functionsthat works on non-Windows.

In April 2018 (or possibly November 2017<ref>{{cite web|title=Windows10 Insider Preview Build 17035 Supports UTF-8 as ANSI|url=https://news.ycombinator.com/item?id=15710685|website=Hacker News|access-date=7 May 2018}}</ref>), with insider build 17035 (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.{{efn|1=Found under control panel, "Region" entry, "Administrative" tab, "Change system locale" button.}} This allows for calling "narrow" functions, including <code>fopen</code> and <code>SetWindowTextA</code>, with UTF-8 strings. However this is a system-wide setting and a program cannot assume it is set.

In May 2019, Microsoft added the ability for a program to set the code page to UTF-8 itself,<ref name="Microsoft-UTF-8">{{Citecite web|title=Use the Windows UTF-8 code pagepages -in UWPWindows applicationsapps|url=https://docslearn.microsoft.com/en-us/windows/uwpapps/design/globalizing/use-utf8-code-page |access-date=2020-06-06 |quote=As of Windows Version version&nbsp;1903 (May &nbsp;2019 Updateupdate), you can use the ActiveCodePage property in the appxmanifest for packaged apps, or the fusion manifest for unpackaged apps, to force a process to use UTF-8 as the process code page. [...] <code>CP_ACP</code> equates to <code>CP_UTF8</code> only if running on Windows Version version&nbsp;1903 (May &nbsp;2019 Updateupdate) or above and the ActiveCodePage property described above is set to UTF-8. Otherwise, it honors the legacy system code page. We recommend using <code>CP_UTF8</code> explicitly. |website=docslearn.microsoft.com |language=en-us}}</ref><ref>{{cite web|url=https://skanthak.homepage.t-online.de/quirks.html#quirk31|title=Windows 10 1903 and later versions finally support UTF-8 with the A forms of the Win32 functions}}</ref> allowing programs written to use UTF-8 to be run by non-expert users.

In{{As of|2019}}, Microsoft recommends programmers use UTF-8 (e.g. instead of any other 8-bit encoding),<ref name="Microsoft-UTF-8">{{cite web|title=Use UTF-8 code pages in Windows apps|url=https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page |access-date=2020-06-06 |quote=As of Windows version&nbsp;1903 (May&nbsp;2019 update), you can use the ActiveCodePage property in the appxmanifest for packaged apps, or the fusion manifest for unpackaged apps, to force a process to use UTF-8 as the process code page. [...] <code>CP_ACP</code> equates to <code>CP_UTF8</code> only if running on Windows version&nbsp;1903 (May&nbsp;2019 update) or above and the ActiveCodePage property described above is set to UTF-8. Otherwise, it honors the legacy system code page. We recommend using <code>CP_UTF8</code> explicitly. |website=learn.microsoft.com |language=en-us}}</ref> on Windows and [[Xbox]], and may be recommending its use instead of UTF-16, even stating "UTF-8 is the universal code page for internationalization [and] UTF-16 [..] is a unique burden that Windows places on code that targets multiple platforms."<ref name="Microsoft GDK">{{Cite web |title=UTF-8 support in the Microsoft Game Development Kit (GDK) - Microsoft Game Development Kit |url=https://learn.microsoft.com/en-us/gaming/gdk/_content/gc/system/overviews/utf-8 |access-date=2023-03-05 |website=learn.microsoft.com |date=19 August 2022 |language=en-us |quote=By operating in UTF-8, you can ensure maximum compatibility [..] Windows operates natively in UTF-16 (or WCHAR), which requires code page conversions by using MultiByteToWideChar and WideCharToMultiByte. This is a unique burden that Windows places on code that targets multiple platforms. [..] The Microsoft Game Development Kit (GDK) and Windows in general are moving forward to support UTF-8 to remove this unique burden of Windows on code targeting or interchanging with multiple platforms and the web. Also, this results in fewer internationalization issues in apps and games and reduces the test matrix that's required to get it right.}}</ref> Microsoft does appear to be transitioning to UTF-8, stating it previously emphasized its alternative, and in [[Windows 11]] some system files are required to use UTF-8 and do not require a Byte Order Mark.<ref>{{Cite web|last=themar-msft|title=Customize the Windows 11 Start menu|url=https://docs.microsoft.com/en-us/windows-hardware/customize/desktop/customize-the-windows-11-start-menu|access-date=2021-06-29|website=docs.microsoft.com|language=en-us|quote=Make sure your LayoutModification.json uses UTF-8 encoding.}}</ref> Notepad can now recognize UTF-8 without the Byte Order Mark, and can be told to write UTF-8 without a Byte Order Mark.{{cn|date=November 2022}} Some other Microsoft products are using UTF-8 internally, including Visual Studio<ref>{{cncite web|title=New Options for Managing Character Sets in the Microsoft C/C++ Compiler|url=https://devblogs.microsoft.com/cppblog/new-options-for-managing-character-sets-in-the-microsoft-cc-compiler/#how-the-microsoft-c/c++-compiler-reads-text-from-a-file|website=devblogs.microsoft.com| date=November22 2022February 2016 |language=en |quote=At some point in the past, the Microsoft compiler was changed to use UTF-8 internally. So, as files are read from disk, they are converted into UTF-8 on the fly.}}</ref><ref>{{ cite web | title=validate-charset (validate for compatible characters) | website=docs.microsoft.com |language=en-us | url=https://docs.microsoft.com/en-us/cpp/build/reference/validate-charset-validate-for-compatible-characters | access-date=2021-07-19 | quote=Visual Studio uses UTF-8 as the internal character encoding during conversion between the source character set and the execution character set. }}</ref> and their [[SQL Server 2019]], with Microsoft claiming 35% speed increase from use of UTF-8, and "nearly 50% reduction in storage requirements."<ref>{{Cite web|date=2019-07-02|title=Introducing UTF-8 support for SQL Server|url=https://techcommunity.microsoft.com/t5/sql-server/introducing-utf-8-support-for-sql-server/ba-p/734928|quote=For example, changing an existing column data type from NCHAR(10) to CHAR(10) using an UTF-8 enabled collation, translates into nearly 50% reduction in storage requirements. [..] In the ASCII range, when doing intensive read/write I/O on UTF-8<!-- " " in quote, but ok to strip-->, we measured an average 35% performance improvement over UTF-16 using clustered tables with a non-clustered index on the string column, and an average 11% performance improvement over UTF-16 using a heap. |access-date=2021-08-24|website=techcommunity.microsoft.com|language=en}}</ref>

=== String constants in Visual Studio ===

=== Programming platforms ===

Before 2019 Microsoft's compilers oftencould failnot at producingproduce UTF-8 string constants from UTF-8 source files. TheThis mostis reliabledue to them converting all strings to the locale code page (which could not be UTF-8). At one time the only method isto work around this was to turn ''off'' {{tt|UNICODE}}, and ''not'' mark the input file as being UTF-8 (i.e. do not use a [[UTF-8#Byte order mark|BOM]]), and arrange the string constants to have the UTF-8 bytes. If a BOM was added, a Microsoft compiler will interpret the strings as UTF-8, convert them to UTF-16, then convert them ''back'' into the current locale, thus destroying the UTF-8.<ref>[http://utf8everywhere.org/#faq.literal UTF-8 Everywhere FAQ: How do I write UTF-8 string literal in my C++ code?]</ref> Without(note athat BOMthe and{{tt|u8"text"}} usingproposed asolution single-bytedoes localenot work, Microsoftstring compilersis willstill leavemangled)</ref> the bytesThis inwould amake quotedthe string unchanged. On moderncompiler systemsthink settingboth the codeinput pageand tooutputs UTF-8were helpsin considerably,the but invalidsame single-byte sequenceslocale, areand stillleave notstrings preserved (using {{code|\x}} can work around this)unmolested.

== See also ==