MORE INFORMATION
General Registry Information
The registry is used by applications and Windows to store configuration
data. It is a replacement for the large numbers of INI files that
proliferated on Windows 3.x machines and is also used heavily by OLE.
The registry is organized using a hierarchical series of keys and values
resembling a tree. Each key, beginning with one of the six predefined root
keys, can have sub-keys and values associated with it. The keys are
organizational and naming units and appear in the Windows Registry Editors
as file folders. Values are data entries and appear as text entries in the
right pane of the Registry Editor window. Keys need not have any associated
values, but may have many. Each value has an associated data type. The two
most commonly used registry data types are REG_SZ, a null-terminated
string; and REG_DWORD, a 32-bit number.
The basic process used to write or read from a location in the registry is
the same. To reference any given key or value, you must have a handle to
the key. Once this handle is obtained, values and sub-keys of the key that
this handle refers to can be read, set, or listed (enumerated).
Given a location in the registry, to obtain a handle to that key, you must
begin with one of the six predefined keys (HKEY_CLASSES_ROOT,
HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS, HKEY_CURRENT_CONFIG, and
HKEY_DYN_DATA) and traverse the registry tree until the desired key is
reached. User programs most often read and write from HKEY_CURRENT_USER and
HKEY_LOCAL_MACHINE. If the keys being traversed exist already, you can use
a series of calls to the RegOpenKey or RegOpenKeyEx functions. If the keys
need to be created, the RegCreateKey and RegCreateKeyEx functions do the job.
With the handle to the desired key, the functions used to list, set, and
retrieve information can be called. In all cases, the functions with the Ex
suffix will work only on 32-bit platforms. Functions without the suffix may
work on both 16-bit and 32-bit versions of Windows. Keep in mind that not
all registry functions lacking the 'Ex' suffix are functions provided for
16-bit compatibility. The Ex suffix was only added when the capabilities of
16-bit functions were expanded. Functions that are totally new and specific
to 32-bit platforms do not possess an Ex extension.
The RegSetValue and RegSetValueEx functions allow the settings of a value
to be modified, while RegQueryValue and RegQueryValueEx retrieve the
current setting of a value. The limitations of the non-Ex, 16-bit versions
of these APIs are very evident here. When using the 16-bit RegSetValue
function there is no way to name a value, and because of this, RegSetValue
can't be used to associate more than one value with each key. In addition,
all values written with RegSetValue have a data type of REG_SZ. These
limitations are inherent with the 16-bit Registry. RegSetValueEx allows the
creation of a multiple number of values with any available data type.
How to Write to a Specific Registry Location
After determining what functions you will need to use for your project,
copy the relevant declares from the code at the end of this article to a
basic module. The two Visual Basic procedures included (SetValueEx and
QueryValueEx) are wrappers for the RegSetValueEx and RegQueryValueEx API
functions and greatly simplify their use. The notes below make use of these
Visual Basic functions; however, you are free to make calls directly to the
API if you wish.
Creating/Modifying Keys and Values:
With the declarations and procedures available, you can create and open
keys, and add, modify, and read values. The three following sections
explain how to create a key, set or modify a value, and query a value.
Creating a New Key:
Creating a new key is as simple as using the following procedure.
CreateNewKey takes the name of the key to create, and the constant
representing the predefined key to create the key under. The call to
RegCreateKeyEx doesn't take advantage of the security mechanisms allowed,
but could be modified to do so. A discussion of Registry security is
outside the scope of this article.
Private Sub CreateNewKey (sNewKeyName As String, lPredefinedKey As Long)
Dim hNewKey As Long 'handle to the new key
Dim lRetVal As Long 'result of the RegCreateKeyEx function
lRetVal = RegCreateKeyEx(lPredefinedKey, sNewKeyName, 0&, _
vbNullString, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, _
0&, hNewKey, lRetVal)
RegCloseKey (hNewKey)
End Sub
With this procedure a call of:
CreateNewKey "TestKey", HKEY_LOCAL_MACHINE
will create a key called TestKey immediately under HKEY_LOCAL_MACHINE.
Calling CreateNewKey like this:
CreateNewKey "TestKey\SubKey1\SubKey2", HKEY_LOCAL_MACHINE
will create three-nested keys beginning with TestKey immediately under
HKEY_CURRENT_USER, SubKey1 subordinate to TestKey, and SubKey3 under
SubKey2.
Setting/Modifying a Value:
Creating and setting a value of a specified key can be accomplished with
the following short procedure. SetKeyValue takes the key that the value
will be associated with, the name of the value, the setting of the value,
and the type of the value (the SetValueEx function only supports REG_SZ and
REG_DWORD, but this can be modified if necessary). Specifying a new value
for an existing sValueName will modify the current setting of that value.
Private Sub SetKeyValue (sKeyName As String, sValueName As String, _
vValueSetting As Variant, lValueType As Long)
Dim lRetVal As Long 'result of the SetValueEx function
Dim hKey As Long 'handle of open key
'open the specified key
lRetVal = RegOpenKeyEx(HKEY_CURRENT_USER, sKeyName, 0, _
KEY_SET_VALUE, hKey)
lRetVal = SetValueEx(hKey, sValueName, lValueType, vValueSetting)
RegCloseKey (hKey)
End Sub
A call of:
SetKeyValue "TestKey\SubKey1", "StringValue", "Hello", REG_SZ
will create a value of type REG_SZ called "StringValue" with the setting of
"Hello." This value will be associated with the key SubKey1 of "TestKey."
In this case, "TestKey" is a subkey of HKEY_CURRENT_USER, but this can be
modified by changing the call to RegOpenKeyEx. This call will fail if
"TestKey\SubKey1" does not exist. To avoid this problem, use a call to
RegCreateKeyEx instead of a call to RegOpenKeyEx. RegCreateKeyEx will open
a specified key if it already exists.
Querying a Value:
The next procedure can be used to ascertain the setting of an existing
value. QueryValue takes the name of the key and the name of a value
associated with that key and displays a message box with the corresponding
value. It uses a call to the QueryValueEx wrapper function defined below,
that only supports REG_SZ and REG_DWORD types.
Private Sub QueryValue (sKeyName As String, sValueName As String)
Dim lRetVal As Long 'result of the API functions
Dim hKey As Long 'handle of opened key
Dim vValue As Variant 'setting of queried value
lRetVal = RegOpenKeyEx(HKEY_CURRENT_USER, sKeyName, 0, _
KEY_QUERY_VALUE, hKey)
lRetVal = QueryValueEx(hKey, sValueName, vValue)
MsgBox vValue
RegCloseKey (hKey)
End Sub
With this procedure, a call of:
QueryValue "TestKey\SubKey1", "StringValue"
will display a message box with the current setting of the "StringValue"
value, and assumes that "StringValue" exists in the "TestKey\SubKey1" key.
If the Value that you query does not exist then QueryValue will return an
error code of 2 - 'ERROR_BADKEY'.
Additional Notes:
The above examples use the extended 32-bit versions of the registry
functions exclusively. These functions allow more than one value to be
associated with each key. As discussed above, the 16-bit RegSetValue and
RegQueryValue act on a single value associated with the current key (which
is always of the type REG_SZ). These functions appear in the 32-bit
Registry Editor with a name of <NO NAME>. To set, modify, or query this
special associated value, one must use the 16-bit registry functions.
Reading and writing from the registry in a 16-bit environment is much
simpler than in a 32-bit environment. The same basic procedure is followed:
open a key and get a handle and then call your modification function with
that handle, but no consideration needs to be made for multiple associated
values or for different value data types. A 16-bit application can create
and modify keys and values with the declarations of the RegCreateKey,
RegOpenKey, RegQueryValue, RegSetValue, and RegCloseKey functions.
In some cases, there is no need for any values to be associated with a key.
An application may only need to know if a certain key or value exists, and
not care about the nature of the key's values. In a situation like this,
the RegEnumKey, RegEnumKeyEx, and RegEnumValue functions can be used to
determine whether a certain key or value exists. For more information on
these functions refer to the API Text Viewer and/or Windows API reference.
API Function and Constant Declarations
Option Explicit
Public Const REG_SZ As Long = 1
Public Const REG_DWORD As Long = 4
Public Const HKEY_CLASSES_ROOT = &H80000000
Public Const HKEY_CURRENT_USER = &H80000001
Public Const HKEY_LOCAL_MACHINE = &H80000002
Public Const HKEY_USERS = &H80000003
Public Const ERROR_NONE = 0
Public Const ERROR_BADDB = 1
Public Const ERROR_BADKEY = 2
Public Const ERROR_CANTOPEN = 3
Public Const ERROR_CANTREAD = 4
Public Const ERROR_CANTWRITE = 5
Public Const ERROR_OUTOFMEMORY = 6
Public Const ERROR_ARENA_TRASHED = 7
Public Const ERROR_ACCESS_DENIED = 8
Public Const ERROR_INVALID_PARAMETERS = 87
Public Const ERROR_NO_MORE_ITEMS = 259
Public Const KEY_QUERY_VALUE = &H1
Public Const KEY_SET_VALUE = &H2
Public Const KEY_ALL_ACCESS = &H3F
Public Const REG_OPTION_NON_VOLATILE = 0
Declare Function RegCloseKey Lib "advapi32.dll" _
(ByVal hKey As Long) As Long
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, ByVal lpSecurityAttributes _
As Long, phkResult As Long, lpdwDisposition As Long) As Long
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
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
Declare Function RegQueryValueExLong Lib "advapi32.dll" Alias _
"RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
String, ByVal lpReserved As Long, lpType As Long, lpData As _
Long, lpcbData As Long) As Long
Declare Function RegQueryValueExNULL Lib "advapi32.dll" Alias _
"RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
String, ByVal lpReserved As Long, lpType As Long, ByVal lpData _
As Long, lpcbData As Long) As Long
Declare Function RegSetValueExString Lib "advapi32.dll" Alias _
"RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
ByVal Reserved As Long, ByVal dwType As Long, ByVal lpValue As _
String, ByVal cbData As Long) As Long
Declare Function RegSetValueExLong Lib "advapi32.dll" Alias _
"RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
ByVal Reserved As Long, ByVal dwType As Long, lpValue As Long, _
ByVal cbData As Long) As Long
SetValueEx and QueryValueEx Wrapper Functions:
Public Function SetValueEx(ByVal hKey As Long, sValueName As String, _
lType As Long, vValue As Variant) As Long
Dim lValue As Long
Dim sValue As String
Select Case lType
Case REG_SZ
sValue = vValue & Chr$(0)
SetValueEx = RegSetValueExString(hKey, sValueName, 0&, _
lType, sValue, Len(sValue))
Case REG_DWORD
lValue = vValue
SetValueEx = RegSetValueExLong(hKey, sValueName, 0&, _
lType, lValue, 4)
End Select
End Function
Function QueryValueEx(ByVal lhKey As Long, ByVal szValueName As _
String, vValue As Variant) As Long
Dim cch As Long
Dim lrc As Long
Dim lType As Long
Dim lValue As Long
Dim sValue As String
On Error GoTo QueryValueExError
' Determine the size and type of data to be read
lrc = RegQueryValueExNULL(lhKey, szValueName, 0&, lType, 0&, cch)
If lrc <> ERROR_NONE Then Error 5
Select Case lType
' For strings
Case REG_SZ:
sValue = String(cch, 0)
lrc = RegQueryValueExString(lhKey, szValueName, 0&, lType, _
sValue, cch)
If lrc = ERROR_NONE Then
vValue = Left$(sValue, cch-1)
Else
vValue = Empty
End If
' For DWORDS
Case REG_DWORD:
lrc = RegQueryValueExLong(lhKey, szValueName, 0&, lType, _
lValue, cch)
If lrc = ERROR_NONE Then vValue = lValue
Case Else
'all other data types not supported
lrc = -1
End Select
QueryValueExExit:
QueryValueEx = lrc
Exit Function
QueryValueExError:
Resume QueryValueExExit
End Function