How to query whether a certain item exists about winreg HOT 3 CLOSED

One option could be trying opening the subkey with RegKey::TryOpen(), and then check the result code.
If the result code is 2 (ERROR_FILE_NOT_FOUND), that means that the subkey doesn't exist.
If the result code is 0 (ERROR_SUCCESS), that means that the subkey exists and was correctly opened.

For example:

// Try open the subkey for read
auto result = key.TryOpen(HKEY_CURRENT_USER, LR"(SOFTWARE\Classes\ms)", KEY_READ);
if (result.Code() == ERROR_FILE_NOT_FOUND)
{
    // Doesn't exist
}

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Thank you, I have reviewed the source code and suggest using std::wstring_view instead of const std::wstring & in source code

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Using std::wstring_view instead of const std::wstring& in that context would be really bad and a source of lots of bugs. In fact, typically Win32 C-style APIs (or at least those used in my code), expect PCWSTR as (Unicode UTF-16) input string parameters. PCWSTR is a _Null_terminated_ const wchar_t*; on the other hand, std::wstring_views are not guaranteed to be null terminated! So using them as you suggest would cause lots of (subtle) bugs. Things might be different if the C++ standard library would provide a proper null-terminated version of string views.

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