On 2020-01-29 11:36, Trey Harris wrote:
On Wed, Jan 29, 2020 at 14:01 ToddAndMargo via perl6-users
<perl6-users@perl.org <mailto:perl6-users@perl.org>> wrote:
On 2020-01-29 06:34, Trey Harris wrote:
> I was going to ask about that (but it seemed out of Raku-world,
and I
> don’t even play someone who knows about Windows on TV), but,
okay, I’ll
> bite... what are some examples of the precisely 3-byte + 32-bit
null UTF
> strings you imagine being encoded by this interface? I have never
heard
> of such a small fixed-width UTF data structure before because
it’s just
> so bizarre, and then mandating a null termination so you lose the
4th
> byte that would make this structure at least somewhat coherent as a
> UCS-4 codepoint... since there’s no such thing as UTF-24, I
assume this
> is three UTF-8 bytes packed (which I guess is what you mean by
“little
> endian C string”, but that becomes at best ill-defined abutted
next to
> “UTF”)... But, what on earth is it being used for?
>
> I’m fascinated, in the way a cat is fascinated by a snake....
Trey,
You are basically setting up a buffer of bytes
and then telling the WinAPI how long the
data in the buffer is as well as what type of
data the buffer contains.
That is clear from the document linked at
https://docs.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regsetvalueexw
But what I was asking about and what I don’t understand is what you
meant when you wrote:
where CbData can either be a UTF little endian C string,
terminated by a nul or a four byte little endian
unsigned integer (no two's complement allowed) depending
on the value of lpValueName (REG_SZ, REG_DWORD, etc.)
Can you explain just this part:
where CbData can… be a UTF little endian C string,
terminated by a null
That’s the part I’m fascinated by because it’s just so strange. What’s
an example of a valid value of this type and not the “unsigned integer
(no two’s complement allowed)”?
"Todd" would convert to
84 00 111 00 100 00 100 00 00 00
Here is a more elaborate UTF16 little endian example. It
return the WinAPI error string that goes with the error code
perl6 -I. -e "use lib '.'; use WinErr :WinFormatMessage; say
WinFormatMessage( 0x20, True );"
WinFormatMessage: Debug:
WinGetLastError 0
Error Number 32
nSize 1024
RtnCode 81
Error String Characters 79
ErrorString <The process cannot access the file because
it is being used by another process.>
lpBuffer
84 0 104 0 101 0 32 0 112 0 114 0 111 0 99 0 101 0 115 0 115 0 32 0 99 0
97 0 110 0 110 0 111 0 116 0 32 0 97 0 99 0 99 0 101 0 115 0 115 0 32 0
116 0 104 0 101 0 32 0 102 0 105 0 108 0 101 0 32 0 98 0 101 0 99 0 97 0
117 0 115 0 101 0 32 0 105 0 116 0 32 0 105 0 115 0 32 0 98 0 101 0 105
0 110 0 103 0 32 0 117 0 115 0 101 0 100 0 32 0 98 0 121 0 32 0 97 0 110
0 111 0 116 0 104 0 101 0 114 0 32 0 112 0 114 0 111 0 99 0 101 0 115 0
115 0 46 0 13 0 10 0 0 0 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
-1 -1 -1 -1 -1
The buffer was prefilled with 0xFF (-1) to clearly show
the 0x0000 terminator at the end of the buffer.
I will eMail you off line a test example I am including in
my WinAPI paper.
-T
