12.11 Wide String Constants

A wide string constant stands for an array of 16-bit or 32-bit characters. They are rarely used; if you’re just learning C, you may as well skip this section.

There are three kinds of wide string constants, which differ in the data type used for each character in the string. Each wide string constant is equivalent to an array of integers, but the data type of those integers depends on the kind of wide string. Using the constant in an expression will convert the array to a pointer to its zeroth element, as usual for arrays in C (see Accessing Array Elements). For each kind of wide string constant, we state here what type that pointer will be.

char16_t

This is a 16-bit Unicode wide string constant: each element is a 16-bit Unicode character code with type char16_t, so the string has the pointer type char16_t *. (That is a type designator; see Pointer Type Designators.) The constant is written as ‘u’ (which must be lower case) followed (with no intervening space) by a string constant with the usual syntax.

char32_t

This is a 32-bit Unicode wide string constant: each element is a 32-bit Unicode character code, and the string has type char32_t *. It’s written as ‘U’ (which must be upper case) followed (with no intervening space) by a string constant with the usual syntax.

wchar_t

This is the original kind of wide string constant. It’s written as ‘L’ (which must be upper case) followed (with no intervening space) by a string constant with the usual syntax, and the string has type wchar_t *.

The width of the data type wchar_t depends on the target platform, which makes this kind of wide string somewhat less useful than the newer kinds.

char16_t and char32_t are declared in the header file uchar.h. wchar_t is declared in stddef.h.

Consecutive wide string constants of the same kind concatenate, just like ordinary string constants. A wide string constant concatenated with an ordinary string constant results in a wide string constant. You can’t concatenate two wide string constants of different kinds. In addition, you can’t concatenate a wide string constant (of any kind) with a UTF-8 string constant.