CODEWITHSUNDEEP
c++winapiboostiteratorboost-iterators
Mr.C64
Mr.C64

Reputation: 43014

How to implement a Forward Traversal Iterator for Windows registry enumeration

I was able to use Boost Iterator Facade to build a custom Single Pass Iterator to iterate (in a C++ way) through the values contained in a Windows registry key, wrapping the C API RegEnumValue.

E.g.:

// For each value 'v' under the given registry key 'hKey':
for (const auto& v : RegistryValueIterator(hKey)) 
{
    ...
}

Basically, the iterator's increment method calls RegEnumValue increasing the dwIndex parameter (initially set to 0 in the iterator class constructor), and when ERROR_NO_MORE_ITEMS is returned, that is mapped to the "end" iterator.

I've used the boost::single_pass_traversal_tag:

class RegistryValueIterator
    : public boost::iterator_facade< RegistryValueIterator,
                                     RegistryValueEntry,
                                     boost::single_pass_traversal_tag >
{
    ...

Boost.Filesystem's directory_iterator, which wraps the FindNextFile API in the Windows implementation, is implemented as a single-pass iterator, too. And similarly, the std::experimental::filesystem::directory_iterator is an Input Iterator as well (not a Forward Iterator).

So, would it be possible for registry enumeration to upgrade the iterator category to a Forward Traversal Iterator? What steps should I follow to achieve that goal?

In other words, would it be possible to implement a multi-pass traversal required by Forward Traversal Iterators using the Windows registry APIs like RegEnumValue? If so, how?

P.S. I've discussed registry value enumeration/iteration, but things are very similar for enumerating/iterating through registry keys as well, using the RegEnumKeyEx API.

Upvotes: 1

Views: 235

Answers (0)

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