RegQueryValue() weirdness

Take a look at the following code:

char      buffer[MAX_PATH];
LONG      size = MAX_PATH;

              buffer, &size);

The call to RegQueryValue() returns an error value of 13.
However, GetLastError() indicates there was no error, and the variables buffer and size get set to the correct values.

Where does this error 13 come from???

(I use RegQueryValue() and not RegQueryValueEx() because I want the default value associated with the key, and it is also simpler.)
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Why don't you try to RegOpenKey() first before RegQueryValue():

HKEY hDestKey;
RegOpenKey(HKEY_CLASS_ROOT, "\\wherever...", &hDestKey);
RegQueryValue(.....same as what you did.....);
What type of data is it that you are trying to read (REG_SZ, REG_DWORD and so on) ?
alexoAuthor Commented:
Why should I?

The documentation says: RegQueryValue(key, subkey, ...)
The key I use is HKEY_CLASSES_ROOT, which is open by definition.

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alexoAuthor Commented:
I try to read the default value.
Regedit says it is a string.

Thui is correct, you MUST open the key first.  The document also fooled me when I tried registry at the first time, I think it actually means that if you want to open a key which is the immediate child of HKEY_***, you can do it directly.

Just add this call and you will see the difference.
alexoAuthor Commented:
So how comes I still get the correct answer?
And GetLastError() returns zero - meaning no error.

alexoAuthor Commented:
Time to reopen the question.

The error code of 13 is defined in WINERROR.H as ERROR_INVALID_DATA.  But since you're using 16-bit RegQueryValue(), GetLastError() does not apply.  GetLastError() is only maintained on a per-thread basis.  Even though you get the string okay, it is still not recommended.  You REALLY do need to RegOpenKey/Ex() first and finish with RegCloseKey().

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alexoAuthor Commented:
Is RegQueryValue() a 16-bit API?  Where does it says so.
Why GetLastError() does not apply to 16-bit APIs?

RegQueryValue() is indeed a 16-bit API.  In face, MSDN strongly suggest that 32-bit application to use the equivalent 32-bit RegQueryValueEx() API.  Even MSVC's help book has that also.  The same document also mentioned that GetLastError() is only maintained on a per-thread basis.  And as you may know, 16-bit has its own one-and-only thread in the system.
alexoAuthor Commented:
OK.  That seems to wrap it up.

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