CODEWITHSUNDEEP
c++winapiregistry
Mr.C64
Mr.C64

Reputation: 42924

Invoking RegCloseKey on a predefined registry key handle

Consider the case of a C++ wrapper class around raw HKEY handles.

The wrapper class has a constructor overload taking a HKEY handle as input: the constructed object takes ownership of the input raw handle.
The destructor invokes RegCloseKey() on the wrapped handle, stored in a HKEY m_hKey data member.

Now, consider the case in which a predefined handle like HKEY_CURRENT_USER is passed to the constructor overload. The HKEY_CURRENT_USER value is assigned to the m_hKey member.

The destructor calls RegCloseKey() on that predefined key. In my experiments the API returns 0 in this case, meaning: success. So, is it fine to call RegCloseKey() on predefined registry key handles? Or should a further check be implemented, like:

RegistryKey::~RegistryKey()
{
    if ((m_hKey != nullptr) && !IsPredefinedKey(m_hKey))
        ::RegCloseKey(m_hKey); 
}

Upvotes: 3

Views: 662

Answers (2)

Anders
Anders

Reputation: 101616

I cannot find official documentation that says it is OK but I know it works.

The closest I got was this book:

You can actually call RegCloseKey on one of the predefined root key entries.

It probably happens a lot in the wild so I cannot imagine that Microsoft would change this in the future but without official documentation it is really up to you if you want to risk it or not.

Upvotes: 1

Phil Brubaker
Phil Brubaker

Reputation: 1277

The MSDN doc for the RegOpenKey function infers that you would only want to call RegCloseKey on a handle which you've programmatically created.

...If the key is not one of the predefined registry keys, call the RegCloseKey function after you have finished using the handle.

Upvotes: 3

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