Thread: Registry keys

Given two HKEYs, original and copy, where copy is a copy of original obtained through RegOpenKeyEx by passing 0 as name, is there a way to find out if these two point to the same key?

Example. I have written an iterator over registry keys (Codeplug knows this).

The iterator essentially looks like this:

Code:

class reg_key_iterator {
	// Used for RegEnumKeysEx
	HKEY parent;
	DWORD index;

public:
	reg_key_iterator(HKEY p, DWORD i)
		: index(i)
	{
		internal::regCopyKey(p, KEY_ALL_ACCESS, parent);
	}
}

internal::regCopyKey just calls RegOpenKeyEx to copy the handle p into parent.

Code:

::RegOpenKeyEx(in, 0, 0, sam, &out);

The problem is, if I create two iterators over the same key with this, I need to compare them, and parent == o.parent doesn't work, because the handles have different values.
The iterator copies the key to avoid other objects closing the handle.

Is there a way I can find out if two HKEYs with distinct values point to the same key?

Thx in advance.

I used the second solution. Is this shared_hkey correct?

Code:

class shared_hkey {
	HKEY key;
	long *refcount;
public:
	shared_hkey()
		: key(0), refcount(0)
	{
	}
	shared_hkey(HKEY h)
		: key(h)
	{
		refcount = new long;
		*refcount = 1;
	}
	shared_hkey(const shared_hkey &o)
		: key(o.key), refcount(o.refcount)
	{
		if(refcount) {
			++*refcount;
		}
	}
	~shared_hkey() {
		reset(0);
	}
	shared_hkey &operator =(const shared_hkey &o) {
		if(o != *this) {
			reset(0);
			key = o.key;
			refcount = o.refcount;
			++*refcount;
		}
		return *this;
	}
	void reset(HKEY h) {
		if(h != key && refcount) {
			if(--*refcount == 0) {
				delete refcount;
				refcount = 0;
				regCloseKey(key);
				key = 0;
			}
		}
		key = h;
		if(key) {
			refcount = new long;
			*refcount = 1;
		}
	}
	operator HKEY() const {
		return key;
	}
	bool operator ==(const shared_hkey &o) {
		return key == o.key;
	}
	bool operator !=(const shared_hkey &o) {
		return key != o.key;
	}
};

Thanks a lot. Works like a charm.

Now I need to get my dialog stream buffer properly working, but that's another project