Questions about MSDN for some DDK functions
- From: "Norman Diamond" <ndiamond@xxxxxxxxxxxxxxxx>
- Date: Fri, 8 Jul 2005 18:51:54 +0900
1. http://msdn.microsoft.com/library/default.asp?url=/library/en-us/kmarch/hh/kmarch/k109_81806669-d742-4cb9-b4dd-d7e40fef171a.xml.asp says:
Return Value RtlUpcaseUnicodeChar returns the uppercase version of the specified Unicode character.
MSDN gives no exceptions. Even if the uppercase version of the specified Unicode character requires two Unicode characters to express, RtlUpcaseUnicodeChar returns it in one WCHAR. May I express some doubts about this definition?
2. http://msdn.microsoft.com/library/en-us/kmarch/hh/kmarch/k109_c1a13e9a-f863-4bcd-ae89-daee0c3d3a4b.xml.asp says:
Return Value RtlUpperChar returns the uppercase version of the specified character or returns the value specified by the caller for Character if the specified character cannot be converted.
That makes sense. In a case where the relevant ANSI character fits in a single byte and was specified, but the uppercase version requires two ANSI characters and therefore cannot be converted, we can figure out what this function will do.
The page continues:
RtlUpperChar returns the input Character unconverted if it is the lead byte of a multibyte character or if the uppercase equivalent of Character is a double-byte character. To convert such characters, use RtlUpcaseUnicodeChar.
That makes sense too. If the relevant ANSI character doesn't fit in a single byte then we have to convert the character from ANSI to Unicode, then call RtlUpcaseUnicodeChar, then convert the result from Unicode to ANSI.
But something is missing. If the relevant ANSI character does fit in a single byte but cannot be directly converted, then in this case also should we convert the character from ANSI to Unicode and call RtlUpcaseUnicodeChar and convert the result back? I think not because of problem 1 above. So there is still no way?
3. http://msdn.microsoft.com/library/default.asp?url=/library/en-us/kmarch/hh/kmarch/k109_c1a13e9a-f863-4bcd-ae89-daee0c3d3a4b.xml.asp says (for RtlUpperString):
The number of bytes copied from SourceString is either the Length of SourceString or the MaximumLength of DestinationString, whichever is smaller.
So even if the MaximumLength of DestinationString is longer than the Length of SourceString and is also long enough to hold the entire uppercase conversion of SourceString, RtlUpperString will still truncate the result at the Length of SourceString, will waste the remaining available space, and will lose some of the characters that should have been converted. Why?
4. A little bird told me why RtlIsValidOemCharacter isn't documented. Probably the thing takes a single byte parameter and returns a single byte result and is thoroughly incapable of distinguishing valid OEM characters from garbage. But why is the thing exported? Are there really some callers that call it? If so, aren't the callers guaranteed to fail? Wouldn't it be better to delete the function RtlIsValidOemCharacter entirely?
(Where I live, Microsoft products default to code page 932 for both ANSI and OEM. The contents of boot.ini are read and displayed in Shift-JIS not Unicode. I've also seen a Microsoft product with a different default code page where one particular single byte lowercase letter uppercases to SS, but didn't experiment with kernel mode programming in it.)
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