Representation of wchar_t and char in WinDbg

Question

Note:

/*
* Trivial code
*/
wchar_t *greeting = L"Hello World!";
char *greeting_ = "Hello World!";

WinDbg:

0:000> ?? greeting
wchar_t * 0x00415810
"Hello World!"
0:000> ?? greeting_
char * 0x00415800
"Hello World!"

0:000> db 0x00415800
00415800  48 65 6c 6c 6f 20 57 6f-72 6c 64 21 00 00 00 00  Hello World!....
00415810  48 00 65 00 6c 00 6c 00-6f 00 20 00 57 00 6f 00  H.e.l.l.o. .W.o.
00415820  72 00 6c 00 64 00 21 00-00 00 00 00 00 00 00 00  r.l.d.!.........

Question:

• What is the purpose of the NULL character: 00 between ASCII characters in wchar_t - Win32?

Answer 1

wchar_t is a wide-character string, so each character takes 2 bytes of storage. 'H' as a wchar_t is 0x0048. Since x86 is little-endian, you see the bytes in memory in order 48 00.

db in windbg will dump the bytes and provide how its viewed as an ASCII string, hence the H.E.L. ... output you see. You can use 'du' to dump the memory as a unicode string.

Answer 2

The answer is that wchar_t characters are 16-bit quantities, thus requiring two bytes each. Each represents a UTF-16 character. Since the letters you're using are within the ASCII range, they have values < 256, so the high byte is zero for each 2-byte pair.