A Class For Handling The Registry

Often one can read in the newsgroups, that someone is looking for an MFC class that encapsulates the registry. In fact, MFC does not provide such a class. As long as one has no need to work with the registry in another location than HKEY_CURRENT_USER\Software\[<company>\]<product>, one can use CWinApp::GetProfile*() and CWinApp::WriteProfile*().

If one wants to use the registry more flexible, then one has to use the API-functions with their dozens of parameters. I don't know why MS doesn't provide a registry class in MFC - that would be quite easy ...

The CRegistry class I've developed allows one to use the registry in a simple way. In addition to the basic operations (loading and storing data), the class provides some more features. For instance one can walk the registry tree and perform some operations on any key/value-hit. Furthermore the class encapsulates differences between NT and Win95 (Aeh - you guessed that the Win32 API should be identical on both systems? Yes - the API is identical, but the performed action is not! Take a closer look at the description of the RegDeleteKey() function for instance.)

To handle all the different data types one can put into the registry, the CRegistry class uses an information holder class CRegVal. If you have to load a string from
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\WinLogon\DefaultUserName
you can do it as follows:

CString strKey = TEXT("Software\\Microsoft\\Windows NT\\CurrentVersion\\WinLogon");
CRegistry reg(HKEY_LOCAL_MACHINE);  // otherwise it defaults to HKEY_CURRENT_USER
CString strDefaultUserName;
CRegVal regval;
if( reg.LoadKey(strKey, TEXT("DefaultUserName"), regval) )
        if( regval.GetValue(strDefaultUserName) )
                // yep - got the name

CString strKey = TEXT("Software\\Microsoft\\Windows NT\\CurrentVersion\\WinLogon");
CRegistry reg(HKEY_LOCAL_MACHINE);  // otherwise it defaults to HKEY_CURRENT_USER
CString strDefaultUserName;
if( reg.LoadKey(strKey, TEXT("DefaultUserName"), strDefaultUserName) )
        // yep - got the name

CRegistry doesn't support security (but that was no handicap for me so far :-)
 

Changes in Revision 2

Changes in Revision 3

• The RegistryTreeWalk() method no longer reports a wrong  "depth" to the methods OnValueHit() and OnKeyHit().
• The member USHORT m_usDepth was deleted
• eliminated a memory leak in DeleteKey()  (thanks to Tobias Krueger)
• several bugfixes in DeleteKey() (sent in by Tobias Krueger)

 Changes in Revision 4

• Some of the CRegVal::SetValue() methods changed. Most changes are for UNICODE applications (allocated too less memory). CRegVal::SetValue(const CStringArray &) is the only method that changes even for non-UNICODE applications. If you write CStringArrays to the registry, you really should upgrade to this revision!

Changes in Revision 5

• Bug fixed in the RegTreeWalk-function (thanks to Pieter E. Roos and Daniel G. Hyams): The RegEnumValue()  function returns the number of bytes read in the last parameter. Since that value is stored in the CRegVal helper class, the next time RegVal was used to receive information from RegEnumValue(), RegEnumValue() thought that the buffer that it can put data in is smaller than it really is.
• The sample is now a VC 6 project (sorry to all of you, who have only older versions of VC - but I have to be up to date ...)

Usage

CRegistry consists of three files:
Registry.h
Registry.cpp
RegMFC.cpp
Download Source 12 KB
Download Sample Project 28 KB

Date Last Updated: February 3, 1999