A question regarding RegSetValueEx

Here is the definition of RegSetValueEx,
LONG WINAPI RegSetValueEx(
__in HKEY hKey,
__in_opt LPCTSTR lpValueName,
__reserved DWORD Reserved,
__in DWORD dwType,
__in_opt const BYTE *lpData,
__in DWORD cbData
);

According to MSDN, If the data is of type REG_SZ, REG_EXPAND_SZ, or REG_MULTI_SZ, cbData must include the size of the terminating null character or characters. But I tried to specify the cbData without considering terminating null character, it still works. It means, for example, if lpData points to _T("dullboy"), I specify cbData as 14, it still works as I specify cbData as 16. Would anybody here explain why? Thanks for your inputs.

Maybe you got lucky and the memory after the end of the char buffer was zero'd?

Maybe the api checks for a terminating null at length - 1 and writes one out if it doesn't find one (or appends two nulls for multi-sz).

A function detects the end of a string either by using the null terminator or by using a parameter for the lenght of the string. It only uses one of the two methods. So, if there is a parameter for the string lenght, the null terminator is ignored. Present or absent, it doesn't matter, the function will only take the declared lenght, regardless of whats's after that.

Are you sure your application is using Unicode? If not, then either 14 or 16 is more than enough.

Quote:

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Originally Posted by dullboy

Here is the definition of RegSetValueEx,
LONG WINAPI RegSetValueEx(
__in HKEY hKey,
__in_opt LPCTSTR lpValueName,
__reserved DWORD Reserved,
__in DWORD dwType,
__in_opt const BYTE *lpData,
__in DWORD cbData
);

According to MSDN, If the data is of type REG_SZ, REG_EXPAND_SZ, or REG_MULTI_SZ, cbData must include the size of the terminating null character or characters. But I tried to specify the cbData without considering terminating null character, it still works. It means, for example, if lpData points to _T("dullboy"), I specify cbData as 14, it still works as I specify cbData as 16. Would anybody here explain why? Thanks for your inputs.

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Windows registry strings are natively stored as UTF-16.

If your project is compiled as Unicode, then I would definitely follow the guidelines.
This is what I do:
DWORD cbData = (_tcslen(str)+1) * sizeof(TCHAR);