Knowledge Base

How To Enumerate the Subkeys of an Open Registry Key

Article ID: 267908

Article Last Modified on 7/15/2004

APPLIES TO

Microsoft Visual Basic 5.0 Professional Edition
Microsoft Visual Basic 6.0 Professional Edition
Microsoft Visual Basic 5.0 Enterprise Edition
Microsoft Visual Basic 6.0 Enterprise Edition

This article was previously published under Q267908

SUMMARY

This article provides an example of how to use API functions to programmatically find keys in the system registry. The sample demonstrates searches of root subkeys for specified text strings. An option to perform case-sensitive text searches is presented.

The example uses the RegEnumKeyEx API function to enumerate subkeys of a specified open registry key. The function retrieves information about one subkey each time it is called.

MORE INFORMATION

The following steps create a project that displays the subkeys of an open registry key in a list box. You can use search criteria to isolate specific keys to be returned.

Step-by-Step Example

Start a new project Standard EXE in Visual Basic. Form1 is created by default.
Set the BorderStyle property of Form1 to 4 - FixedToolWindow.
Add the following controls to Form1: three Labels, two ComboBoxs, one TextBox, two CommandButtons, one CheckBox, and one ListBox.
Set the Style property for each ComboBox to 2 - Dropdown List.

Add the following code to the General Declarations section of Form1:

Option Explicit

Private Type FILETIME
    intLow As Long
    intHigh As Long
End Type

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, phkResult As Long) As Long

Private Declare Function RegEnumKeyEx Lib "advapi32.dll" _
    Alias "RegEnumKeyExA" _
    (ByVal hKey As Long, _
    ByVal dwIndex As Long, _
    ByVal lpName As String, _
    lpcbName As Long, _
    ByVal lpReserved As Long, _
    ByVal lpClass As String, _
    lpcbClass As Long, _
    lpftLastWriteTime As FILETIME) As Long

Private Declare Function RegCloseKey Lib "advapi32.dll" _
    (ByVal hKey As Long) As Long

Const HKEY_CLASSES_ROOT = &H80000000
Const HKEY_CURRENT_USER = &H80000001
Const HKEY_LOCAL_MACHINE = &H80000002
Const HKEY_USERS = &H80000003

Const ERROR_SUCCESS = 0&

Const SYNCHRONIZE = &H100000
Const STANDARD_RIGHTS_READ = &H20000
Const KEY_QUERY_VALUE = &H1
Const KEY_ENUMERATE_SUB_KEYS = &H8
Const KEY_NOTIFY = &H10
Const KEY_READ = ((STANDARD_RIGHTS_READ Or _
                  KEY_QUERY_VALUE Or _
                  KEY_ENUMERATE_SUB_KEYS Or _
                  KEY_NOTIFY) And _
                  (Not SYNCHRONIZE))

Dim strBranch As Long

Private Sub Combo1_Click()
    ' Set the branch to search depending on
    ' what is selected in the ComboBox
    Select Case Combo1.ListIndex
        Case 0
            strBranch = HKEY_CLASSES_ROOT
        Case 1
            strBranch = HKEY_CURRENT_USER
        Case 2
            strBranch = HKEY_LOCAL_MACHINE
        Case Else
            strBranch = HKEY_USERS
    End Select
End Sub

Private Sub Command1_Click()
    Dim i As Integer
    Dim lngKeyHandle As Long
    Dim lngResult As Long
    Dim lngCurIdx As Long
    Dim strValue As String
    Dim lngValueLen As Long
    Dim strClass As String
    Dim lngClassLen As Long
    Dim strResult As String
    Dim lngTime As FILETIME
    Dim strSearch As String
    Dim intSearchLen As Integer
    Dim blnMatch As Boolean
    
    i = 0
    ' Clear the current results
    List1.Clear
    ' Assign the new string to search for
    strSearch = Text1.Text
    intSearchLen = Len(strSearch)
    
    ' Open the Root Branch to search
    lngResult = RegOpenKeyEx(strBranch, _
            "", _
             0&, _
             KEY_READ, _
             lngKeyHandle)
    
    If lngResult <> ERROR_SUCCESS Then
        MsgBox "Cannot open key.", , "Search Registry Keys"
    Else
    ' If the Root branch can be opened, disable
    ' the buttons and begin the search
        Command1.Enabled = False
        Command2.Enabled = False
        List1.Enabled = False
        Form1.MousePointer = 11
        
        lngCurIdx = 0
        Do
            lngValueLen = 2000
            strValue = String(lngValueLen, 0)
            lngClassLen = 2000
            strClass = String(lngClassLen, 0)
        
            ' Enumerate all the sub keys
            lngResult = RegEnumKeyEx(lngKeyHandle, _
                 lngCurIdx, _
                 ByVal strValue, _
                 lngValueLen, _
                 0&, _
                 ByVal strClass, _
                 lngClassLen, _
                 lngTime)
           
            ' Increment the index of found keys
            lngCurIdx = lngCurIdx + 1
        
            If lngResult = ERROR_SUCCESS Then
                ' Trim the current key to its actual length
                strResult = Left(strValue, lngValueLen)
                
                ' Eliminate case if the search is insensitive
                blnMatch = False
                strValue = strResult
                If Check1.Value = 0 Then
                    strResult = LCase(strResult)
                    strSearch = LCase(strSearch)
                End If

                ' Compare strings based upon search type
                Select Case Combo2.ListIndex
                    Case 0
                        ' Check if any portion of the search string is found.
                        If InStr(strResult, strSearch) Then blnMatch = True
                    Case 1
                        ' Check if an exact match is found.
                        If strResult = strSearch Then blnMatch = True
                    Case 2
                        ' Check if the search string matches the
                        ' left portion of the key string.
                        If Left(strResult, intSearchLen) = strSearch Then blnMatch = True
                    Case Else
                        ' Check if the search string matches the 
                        ' right portion of the key string.
                        If Right(strResult, intSearchLen) = strSearch Then blnMatch = True
                End Select
                
                ' Populate the list with keys that match
                ' the search criteria
                If blnMatch Then
                    i = i + 1
                    List1.AddItem strValue
                End If
            End If
        
        ' Keep looking for more keys
        Loop While lngResult = ERROR_SUCCESS
        ' Close the Root Branch
        lngResult = RegCloseKey(lngKeyHandle)
    
        ' Enable the buttons
        Form1.MousePointer = 0
        List1.Enabled = True
        Command1.Enabled = True
        Command2.Enabled = True
        
        ' Display the total matches
        MsgBox "Total matches:" & Str(i), , "Search Registry Keys"
    End If
End Sub

Private Sub Command2_Click()
    Unload Me
End Sub

Private Sub Form_Load()
    ' Set up the Form interface
    Form1.Caption = "Search Registry Keys"
    Form1.Move 0, 0, 6960, 4230
    
    Label1.Caption = "Search Branch:"
    Label1.Move 240, 240, 1215, 255
    
    Label2.Caption = "Search Mode:"
    Label2.Move 240, 720, 1215, 255
    
    Label3.Caption = "Find What:"
    Label3.Move 240, 1200, 1215, 255

    Combo1.Move 1680, 240, 2535
    Combo1.AddItem "HKEY_CLASSES_ROOT"
    Combo1.AddItem "HKEY_CURRENT_USER"
    Combo1.AddItem "HKEY_LOCAL_MACHINE"
    Combo1.AddItem "HKEY_USERS"
    Combo1.ListIndex = 0
    Combo1.TabIndex = 0
    
    Combo2.Move 1680, 720, 2535
    Combo2.AddItem "Portion"
    Combo2.AddItem "All"
    Combo2.AddItem "Left"
    Combo2.AddItem "Right"
    Combo2.ListIndex = 0
    Combo2.TabIndex = 1
    
    Text1.Move 1680, 1200, 2535, 350
    Text1.Text = ""
    Text1.TabIndex = 2
    
    Command1.Caption = "Find Keys"
    Command1.Move 4560, 240, 1935, 375
    Command1.TabIndex = 3
    Command1.Default = True
    
    Command2.Caption = "Close"
    Command2.Move 4560, 720, 1935, 375
    Command2.TabIndex = 4
    
    Check1.Caption = "Match Case"
    Check1.Move 4680, 1320, 1275, 255
    Check1.TabIndex = 5

    List1.Move 240, 1920, 6255, 1620
    List1.TabIndex = 6
End Sub

Run the project and execute a search. Note that Keys that match the search criteria are displayed in the ListBox.

REFERENCES

For more information the Registry API functions, please search on the following topics in either the Win32 Programmer's Reference or the Microsoft Developer Network (MSDN) Library CD-ROM:

RegCloseKey
RegEnumKeyEx
RegOpenKeyEx

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

145679 How To Use the Registry API to Save and Retrieve Setting

Additional query words: win32 winapi

Keywords: kbhowto kbregistry kbapi kbcodesnippet KB267908

Microsoft KB Archive/267908

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