Searching the Registry

Question:
Using VB 5.0, how can I detect the default browser and launch it to go to user selected site?

Answer:
This information is located in the Registry under this key:HKEY_CLASSES_ROOTHTMLFileShellOpenCommandTo read it, you need to use the Registry API. The following is a sectionfrom my new book discussing the Registry API and how to use it. Sorry forthe bad formatting, but I had to copy it from Microsoft Word. You shouldbe able to find your way through it.

The first function we need is one to retrieve information. There areactually several different API calls involved to do this, so we’re going toencapsulate them all in a simple function that you can use in anyapplication you have.

To get started, do the following:

  1. Open up your Bookmark Viewer program and create a new code module.Since you’ll probably want to use this code in another application, wedon’t want to clutter the Bookmark Viewer variables file with this code.
  2. The GetRegistryKey function code is listed below:
    Public Function GetRegistryKey(sKeyName As String, _   sValue As String, _   Optional bClasses_Root As Boolean = False, _   Optional bCurrent_User As Boolean = False, _   Optional bLocal_Machine As Boolean = False, _   Optional bUsers As Boolean = False, _   Optional bCurrent_Config As Boolean = False, _   Optional bDyn_Data As Boolean = False) As String      Dim sReturnBuffer As String   Dim iBufLen As Long   Dim iReturn As Long   Dim iTree As Long   Dim hKeyHandle As Long      If bClasses_Root Then      iTree = HKEY_CLASSES_ROOT   ElseIf bCurrent_User Then      iTree = HKEY_CURRENT_USER   ElseIf bLocal_Machine Then      iTree = HKEY_LOCAL_MACHINE   ElseIf bUsers Then      iTree = HKEY_USERS   ElseIf bCurrent_Config Then      iTree = HKEY_CURRENT_CONFIG   ElseIf bDyn_Data Then      iTree = HKEY_DYN_DATA   Else      GetRegistryKey = “”      Exit Function   End If   ‘   ‘ Set up return buffer   ‘   sReturnBuffer = Space(BUFFER_LENGTH)   iBufLen = BUFFER_LENGTH      iReturn = RegOpenKeyEx(iTree, sKeyName, _      0, KEY_ALL_ACCESS, hKeyHandle)      If iReturn = ERROR_SUCCESS Then      iReturn = RegQueryValueExString(hKeyHandle, _         sValue, 0, 0, sReturnBuffer, iBufLen)      If iReturn = ERROR_SUCCESS Then         GetRegistryKey = Left$(sReturnBuffer, _            iBufLen – 1)      Else         GetRegistryKey = “”      End If   Else      GetRegistryKey = “”   End If   RegCloseKey hKeyHandle   End Function
    Before we jump into this function, let’s take a quick look at a realregistry key and settings. Start the Registry Editor and find your waydown to this key:
    HKEY_CURRENT_USERSoftwareMicrosoftMS Setup (ACME)User Info
    Once you click on that key, values will be displayed in the right hand sideof the window. The GetRegistryKey function mimics what you just did:
    • You found the key in the registry.
    • You looked at the values in that key.
    • You closed the Registry (and the key)
    If you understand that process, the code is going to be a breeze. The firstlong If/Then block determines which section of the registry the key is in.The six optional parameters correspond to the six sections of the Windows95 registry. Windows NT has additional sections, but we won’t be coveringthose here.

    Based on which section the user specified, a constant value is stored inthe iTree variable for later use. Next, we create a return buffer for theAPI call to put its data into. For any API call that returns data you mustcreate a buffer in exactly this way or you run the risk of crashing yourprogram.

    The next statement actually calls the API function to open the key. If wewere trying to get to the key we just looked at, we could send in either ofthese two strings:

    SoftwareMicrosoftMS Setup (ACME)User InfoSoftwareMicrosoftMS Setup (ACME)User Info
    The Registry functions are case insensitive and do not care if you have abackslash at the beginning or end of the key value.

    If that call was successful, two things have happened:

    • A successful return code was put in the iReturn variable.
    • A handle, or reference, to the key was stored in the hKeyHandle variable.
    We can now retrieve particular values from that key using theRegQueryValueExString API call. That API call uses the handle from theprevious call and returns the values in the buffer we created earlier.

    If that call was also successful, we need to trim off the null terminatorat the end of the buffer. In case you’re not a C/C++ programmer, a nullterminator is how C programmers mark the end of a string. Unfortunately,that character makes it back to VB-land so we have to trim it off. Luckilythe RegQueryValueExString API call sets the iBufLen variable to the lengthof the string it returned, which includes the null character. A quick callto the Left$ function trims the string right up. Finally a call to RegCloseKey cleans up the reference to the Registry andwe’re all done!

  3. Before you can use this code, you have to add quite a few constants andAPI declarations at the beginning of your code module. These are listedhere for your convenience:
    Private Declare Function RegCloseKey Lib “advapi32.dll” _   (ByVal hKey As Long) As LongPrivate Declare Function RegCreateKeyEx Lib _   “advapi32.dll” _   Alias “RegCreateKeyExA” _   (ByVal hKey As Long, ByVal lpSubKey As String, _   ByVal Reserved As Long, ByVal lpClass As String, _   ByVal dwOptions As Long, ByVal samDesired As Long, _   lpSecurityAttributes As Any, _   hKeyHandle As Long, lpdwDisposition As Long) As LongPrivate Declare Function RegQueryValueExString Lib _       “advapi32.dll” _   Alias “RegQueryValueExA” _   (ByVal hKey As Long, ByVal lpValueName As String, _   ByVal lpReserved As Long, lpType As Long, _   ByVal lpData As String, lpcbData As Long) As Long   Private Declare Function RegOpenKeyEx Lib _   “advapi32.dll”_   Alias “RegOpenKeyExA” _   (ByVal hKey As Long, ByVal lpSubKey As String, _   ByVal ulOptions As Long, ByVal samDesired As Long, _   hKeyHandle As Long) As Long   Private Declare Function RegSetValueEx Lib “advapi32.dll” _   Alias “RegSetValueExA” _   (ByVal hKey As Long, ByVal lpValueName As String, _   ByVal Reserved As Long, ByVal dwType As Long, _   lpData As Any, ByVal cbData As Long) As LongPublic Const ERROR_SUCCESS = 0&Public Const HKEY_CLASSES_ROOT = &H80000000Public Const HKEY_CURRENT_CONFIG = &H80000005Public Const HKEY_CURRENT_USER = &H80000001Public Const HKEY_DYN_DATA = &H80000006Public Const HKEY_LOCAL_MACHINE = &H80000002Public Const HKEY_USERS = &H80000003Public Const KEY_CREATE_SUB_KEY = &H4Public Const KEY_ENUMERATE_SUB_KEYS = &H8Public Const KEY_QUERY_VALUE = &H1Public Const KEY_SET_VALUE = &H2Public Const KEY_NOTIFY = &H10Public Const KEY_CREATE_LINK = &H20Public Const REG_OPTION_NON_VOLATILE = 0Public Const REG_SZ = 1Public Const STANDARD_RIGHTS_ALL = &H1F0000Public Const SYNCHRONIZE = &H100000Private Const BUFFER_LENGTH = 255Public Const KEY_ALL_ACCESS = ((STANDARD_RIGHTS_ALL Or _   KEY_QUERY_VALUE Or _   KEY_SET_VALUE Or _   KEY_CREATE_SUB_KEY Or _   KEY_ENUMERATE_SUB_KEYS Or _   KEY_NOTIFY Or _   KEY_CREATE_LINK) And (Not SYNCHRONIZE))
    Note that some of these API calls have not yet been used. They will beused in the SaveRegistryKey function we’ll build next. To test out your function, you can add the following statement somewhere inyour code. This will retrieve the default web browser. You can use thisin a Shell statement to start a browser for a web site, if need be.
    Debug.Print GetRegistryKey(“htmlfileshellopencommand”, “”, _      bClasses_Root:=True)
    This will print a result similar to this on your debug window.
    “F:COMMUN~1INTERN~1iexplore.exe” -nohome
    Regardless of what it prints, it will match exactly with the key value atHKEY_CLASSES_ROOThtmlfileshellopencommand. In this case, we used ablank value name since we were looking for the default value of the key.
  4. With the GetRegistryKey function out of the way, let’s look at theSaveRegistryKey function listed here:
    Public Sub SaveRegistryKey(sKey As String, _   sValueName As String, sNewValue As String, _   Optional bClasses_Root As Boolean = False, _   Optional bCurrent_User As Boolean = False, _   Optional bLocal_Machine As Boolean = False, _   Optional bUsers As Boolean = False, _   Optional bCurrent_Config As Boolean = False, _   Optional bDyn_Data As Boolean = False)   Dim sKeyName As String   Dim iReturn As Long   Dim iTree As Long   Dim hKeyHandle As Long      If bClasses_Root Then      iTree = HKEY_CLASSES_ROOT   ElseIf bCurrent_User Then      iTree = HKEY_CURRENT_USER   ElseIf bLocal_Machine Then      iTree = HKEY_LOCAL_MACHINE   ElseIf bUsers Then      iTree = HKEY_USERS   ElseIf bCurrent_Config Then      iTree = HKEY_CURRENT_CONFIG   ElseIf bDyn_Data Then      iTree = HKEY_DYN_DATA   Else      Exit Sub   End If      ‘   ‘ RegCreateKeyEx will open the named key if it exists,    ‘ and create a new one if it doesn’t.   ‘   iReturn = RegCreateKeyEx(iTree, sKey, 0&, _      vbNullString, REG_OPTION_NON_VOLATILE, _      KEY_ALL_ACCESS, 0&, hKeyHandle, iReturn)      ‘   ‘ RegSetValueEx saves the value to the string within    ‘ the key that was just opened.   ‘   iReturn = RegSetValueEx(hKeyHandle, sValueName, 0&, _      REG_SZ, ByVal sNewValue, Len(sNewValue))      ‘   ‘ Close the key   ‘   RegCloseKey hKeyHandle   End Sub
    As you might have guessed, this function is nearly the reverse of theGetRegistryKey function. If the key doesn’t already exist, we have tocreate it. If it is there, we need to open it. Luckily, theRegCreateKeyEx API call will do the right thing as needed; that is, it willbuild a new key if necessary or open an existing one. We then set thevalue and close the key. Somewhere in your code, let’s change your default username with thefollowing call:
    SaveRegistryKey _   “SoftwareMicrosoftMS Setup (ACME)User Info”,    “DefName”, _   “Bill Gates”
    You can now go out to the registry and see that change in that key.

    Now that you have the power to read and edit the registry from code, oneword of caution: the Registry is EXTREMELY fragile. One modified key inthe wrong place and you will be stuck reinstalling Windows from scratch.If you don’t know what a key does or it doesn’t make sense why it is inyour Registry, leave it alone. What you don’t know can kill your system.

    With that caveat out of the way, here are some interesting keys to use forvarious system functions.

    • SoftwareMicrosoftMS Setup (ACME)User Info – These values store thedefault Windows user and company names which are commonly used by setupprograms. Located under the HKEY_CURRENT_USER tree.
    • HTMLFileShellOpenCommand – Retrieves the default web browser, justlike if you had double-clicked an HTML file in Windows Explorer. Locatedunder the HKEY_CLASSES_ROOT tree.
    • SoftwareVB and VBA Program Settings – This is the area where allGetSetting and SaveSetting function calls read and write from. This islocated under the HKEY_CURRENT_USER tree.
    • Word.Document.8ShellOpenCommand – This is the command line to startWord 97. You can append your own file name to the results ofGetRegistryKey. This key is located in the HKEY_CLASSES_ROOT tree.
    • SoftwareMicrosoftWindowsCurrentVersionUninstall – Ever wonder whyprograms keep showing up in the Add/Remove Programs dialog under theControl Panel? If you want to permanently remove a program from showing upthere, remove its key from here. This key is located in theHKEY_LOCAL_MACHINE tree.

      If you decide to use these functions in your own application, be sure thatyou follow the standard for locating your keys. The standard is to createa company key under Software, as in SoftwareMicrosoft. The next part ofthe key is the application name. After that, it’s up to you. You can haveas many levels as necessary. Take a look at SoftwareMicrosoftWindowsfor an example of a huge tree.

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