What exactly are char16_t and char32_t, and where can I find them?

user_2864916 0
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I was looking for char16_t and char32_t, since I’m working with Unicode, and all I could find on the Web was they were inside uchar.h. I found said header inside the iOS SDK (not the macOS one, for some reason), but there were no such types in it. I saw them in a different header, though, but I could not find where they're defined. Also, the info on the internet is scarce at best, so I’m kinda lost here; but I did read wchar_t should not be used for Unicode, which is exactly what I’ve been doing so far, so please help:(

clang constants unicode macos c
2 Answers

char16_t and char32_t are specified in the C standard. (Citations below are from the 2018 standard.)

Per clause 7.28, the header <uchar.h> declares them as unsigned integer types to be used for 16-bit and 32-bit characters, respectively. You should not have to hunt for them in any other header; #include <uchar.h> should suffice.

Also per clause 7.28, each of these types is a narrowest unsigned integer type with required number of bits. (For example, on an implementation that supported only unsigned integers of 8, 18, 24, and 36, and 50 bits, char16_t would have to be the 18-bit size; it could not be 24, and char32_t would have to be 36.)

Per clause 6.4.5, when a string literal is prefixed by u or U, as in u"abc" or U"abc", it is a wide string literal in which the elements have type char16_t or char32_t, respectively.

Per clause 6.10.8.2, if the C implementation defines the preprocessor macro __STDC_UTF_16__ to be 1, it indicates that char16_t values are UTF-16 encoded. Similarly, __STDC_UTF_32__ indicates char32_t values are UTF-32 encoded. In the absence of these macros, no assertion is made about the encodings.

user_2982250

Microsoft has a fair description: https://docs.microsoft.com/en-us/cpp/cpp/char-wchar-t-char16-t-char32-t?view=vs-2017

  • char is the original, typically 8-bit, character representation.

  • wchar is a "wide char", 16-bits, used by Windows. Microsoft was an early adopter of Unicode, unfortunately this stuck them with this only-used-on-Windows encoding.

  • char16 and char32, used for UTF-16 and -32

Most non-Windows systems use UTF-8 for encoding (and even Windows 10 is adopting this, https://en.wikipedia.org/wiki/Unicode_in_Microsoft_Windows#UTF-8). UTF-8 is by far the most common encoding used today on the web. (ref: https://en.wikipedia.org/wiki/UTF-8)

UTF-8 is stored in a series of chars. UTF-8 is likely the encoding you will find simplest to adopt, depending on your OS.

user_4340040
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