Now that we have covered the basic aspects of Visual Basic and the Windows API, we now need to look at how to accomplish more advanced tasks, like enumerating keys from the Windows Registry, values from the Windows registry, backing up the registry and more.

Enumeration of the Windows Registry can be quite tricky at start, but after you have read this article you will be able to create these functions in your sleep.

The registry contains lots of sub-keys that make up the hierarchy of the Windows Registry. You may want to enumerate the keys in the registry, for example if you wanted to create your own registry editor, you would want to be able to enumerate the keys from the registry.

In this section of the article, I will show you how you can enumerate all the sub-keys from the registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\

You can see all the registry keys that they are, so how do me use Visual basic and the Windows API to enumerate these keys.

This can be done using the following Windows API functions:

RegOpenKeyEx

RegEnumKeyEx

RegCloseKey

The RegEnumKeyEx API function has the following parameters:

hKey – This is the opened key handle, that you can find using the RegOpenKeyEx API function (see earlier section for more information).

dwIndex – This is the index of the key that you want to enumerate. You would call this function increasing this parameter until know more data is available for enumerating.

A common mistake that is often made is by the fact that if you ask a person what is the lowest positive number and they will tell you 1, but at all mathematicians will tell you, 0 is the number o start counting from. You should therefore start the first call of the function leaving this parameter as 0 and after each call increase the value by one.

lpName – This is the returned data containing the name of the key, which we have enumerated. This parameter also returns a null character, and must be passed by value (ByVal). You must fix the length of this string before calling this API function to MAX_PATH + 1 (255 + 1), as the Windows API uses fixed length strings.

lpcbName – This is the length of the returned key name, which you can use with the left function to resize the string. When passing this parameter, you must make it equal to MAX_PATH + 1 (255 + 1). After calling this parameter contains the length of the key.

The rest of the parameters for this function are not needed by the Visual Basic programmer and should be left as null (0&).

Now how can you use the function to enumerate keys?

First you need to open the key that you wish to enumerate using the RegOpenKeyEx API function. You would then need to set the counter to 0 for the first key, and then use a do loop to keep enumerating while there is data is available. When there is no more data available, you need to exit the do and close the registry key.

Now for the sample. Create a new standard-EXE project in Visual basic and add a command button, list box to form1. Set the name of the command button to cmdEnumKey and the caption to Enum Keys.

Option Explicit

Private Sub cmdEnumKey_Click()

Dim lKeyHandle As Long, sTemp As String _

, sTempLen As Long, lTemp As Long, _

lIndex As Long

' Declare variables to hold opened key

' handle and error information

lIndex = 0

lTemp = RegOpenKeyEx(HKEY_LOCAL_MACHINE, "SOFTWARE", _

0&, KEY_ALL_ACCESS, lKeyHandle)

Do

sTempLen = 255 + 1

' Set the length that we want to use to size

' the string

sTemp = String(sTempLen, 0)

' Size the string

lTemp = RegEnumKeyEx(lKeyHandle, lIndex, ByVal sTemp, sTempLen, 0&, 0&, 0&, 0&)

' Call the Enum function to return information

If lTemp = REG_NOMOREDATA Then Exit Do

' The Enum function will either return:

' More Data Available or

' No More Data available

' If there is no more data available then we want

' to end the loop

lstKeys.AddItem Left$(sTemp, sTempLen)

' Add the key to the list box after resizing it.

' NB: Re resize the string to remove the null

' character

lIndex = lIndex + 1

' Increase the index count

Loops

Call RegCloseKey(lKeyHandle)

' close the opened key by passing the key handle

sTemp = String(100, 0)

' Fix the length of the string

sTempLen = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM _

Or FORMAT_MESSAGE_IGNORE_INSERTS, vbNullString, lTemp, _

0&, sTemp, Len(sTemp), ByVal 0&)

' Call the format message API function to return

' error information in the form of a string

MsgBox Left$(sTemp, sTempLen)

' Use the length of the error string returned

' to reduce the string back down to size and

' display the message in a message box

If you now add the required declarations and run the project, click on the command button and the keys from the registry will be displayed in the list box.

For a full sample and more detailed comments, you can download the sample, by clicking on the link below.

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