September 22nd, 2021

Converting between UTF-8 strings and UTF-16 strings in C++/WinRT

Raymond Chen

C++/WinRT provides a pair of functions for converting between UTF-8 strings (with code units represented as char) and UTF-16 strings (code units of wchar_t).

The to_string function takes a std::wstring_view of UTF-16 code units and converts them to a UTF-8 string, represented as a std::string.

Conversely, the to_hstring function takes a std::string_view of UTF-8 code units and converts them to a UTF-16 string, represented as a winrt::hstring.

The argument to to_string and to_hstring can be anything convertible to the corresponding string view type. Types that fall into this category include

Type	Converts to
`std::string`	`std::string_view`
`std::wstring`	`std::wstring_view`
`winrt::hstring`	`std::wstring_view`

We’ll put these conversions to good use next time.

Author

Raymond Chen

Raymond has been involved in the evolution of Windows for more than 30 years. In 2003, he began a Web site known as The Old New Thing which has grown in popularity far beyond his wildest imagination, a development which still gives him the heebie-jeebies. The Web site spawned a book, coincidentally also titled The Old New Thing (Addison Wesley 2007). He occasionally appears on the Windows Dev Docs Twitter account to tell stories which convey no useful information.

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Luan Vitor Simião Oliveira September 23, 2021 0

should there also be a to_u16string? and versions that take a u8string_view?
Erik Weitenberg September 23, 2021 · Edited 0

I suppose I get why the wstrings are named like that (string for wide characters) but I’m not sure what to think of hstring (high characters??). You explained a while ago that the H in HRESULT likely means ‘handle’, but I’m not sure that makes sense here.. Any clues? 🙂
- Peter Cooper Jr. September 24, 2021 0
  
  Yeah, I’m pretty sure it’s a “handle” to a string, in some logical sense.
  
  See also Raymond’s Complete Guide to HSTRING: https://devblogs.microsoft.com/oldnewthing/20160615-00/?p=93675
- Harry Johnston September 23, 2021 0
  
  The documentation says that winrt::hstring encapsulates HSTRING, and that HSTRING is a handle to a Windows Runtime string, so I think your guess is correct. The documentation for HSTRING adds “use HSTRING to represent immutable strings in the Windows Runtime” and there are various associate API functions, e.g., WindowsCreateString and WindowsDeleteString.