12.10 Wide Character Constants

A wide character constant represents characters with more than 8 bits of character code. This is an obscure feature that we need to document but that you probably won’t ever use. If you’re just learning C, you may as well skip this section.

The original C wide character constant looks like ‘L’ (upper case!) followed immediately by an ordinary character constant (with no intervening space). Its data type is wchar_t, which is an alias defined in stddef.h for one of the standard integer types. Depending on the platform, it could be 16 bits or 32 bits. If it is 16 bits, these character constants use the UTF-16 form of Unicode; if 32 bits, UTF-32.

There are also Unicode wide character constants which explicitly specify the width. These constants start with ‘u’ or ‘U’ instead of ‘L’. ‘u’ specifies a 16-bit Unicode wide character constant, and ‘U’ a 32-bit Unicode wide character constant. Their types are, respectively, char16_t and char32_t; they are declared in the header file uchar.h. These character constants are valid even if uchar.h is not included, but some uses of them may be inconvenient without including it to declare those type names.

The character represented in a wide character constant can be an ordinary ASCII character. L'a', u'a' and U'a' are all valid, and they are all equal to 'a'.

In all three kinds of wide character constants, you can write a non-ASCII Unicode character in the constant itself; the constant’s value is the character’s Unicode character code. Or you can specify the Unicode character with an escape sequence (see Unicode Character Codes).