wchar ends with single null byte or two of them?

Question

I just don't understand and can't find much info about wchar end.

If it ends with single null byte, how it know it not string end yet, if something like that "009A" represent one of unicode symbols?

If it ends with two null bytes? Well, I am not sure about it, need confirmation.

Answer 1

Since a wide string is an array of wide characters, it couldn't even end in an one-byte NUL. It is a two-byte NUL. (Arrays in C/C++ can only hold members of the same type, so of the same size).

Also, for ASCII standard characters, there always is one or three one-byte 0, as only extended characters start by a non-zero first byte (depending on whether wchar_t is 16 or 32 bit wide - for simplicity, I assume 16-bit and little-endian):

HELLO is 72 00 69 00 76 00 76 00 79 00 00 00

Answer 2

Here you can read a bit more of Wide Characters: http://en.wikipedia.org/wiki/Wide_character#Size_of_a_wide_character

Terminations are L'\0', means a 16-bit null so it's like two 8-bit null chars.

Remember that "009A" is only 1 wchar so is not a null wchar.

Answer 3

In C (quoting the N1570 draft, section 7.1.1):

A wide string is a contiguous sequence of wide characters terminated by and including the first null wide character.

where a "wide character" is a value of type wchar_t, which is defined in <stddef.h> as an integer type.

I can't find a definition of "wide string" in the N3337 draft of the C++ standard, but it should be similar. One minor difference is that wchar_t is a typedef in C, and a built-in type (whose name is a keyword) in C++. But since C++ shares most of the C library, including functions that act on wide strings, it's safe to assume that the C and C++ definitions are compatible. (If someone can find something more concrete in the C++ standard, please comment or edit this paragraph.)

In both C and C++, the size of a wchar_t is implementation-defined. It's typically either 2 or 4 bytes (16 or 32 bits, unless you're on a very exotic system with bytes bigger than 8 bits). A wide string is a sequence of wide characters (wchar_t values), terminated by a null wide character. The terminating wide character will have the same size as any other wide character, typically either 2 or 4 bytes.

In particular, given that wchar_t is bigger than char, a single null byte does not terminate a wide string.

It's also worth noting that byte order is implementation-defined. A wide character with the value 0x1234, when viewed as a sequence of 8-bit bytes, might appear as any of:

• 0x12, 0x34
• 0x34, 0x12
• 0x00, 0x00, 0x12, 0x34
• 0x34, 0x12, 0x00, 0x00

And those aren't the only possibilities.

Answer 4

if you declare

WCHAR tempWchar[BUFFER_SIZE];

you make it null

for (int i = 0; i < BUFFER_SIZE; i++)
            tempWchar[i] = NULL;