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Although Visual Basic includes the SaveSetting and GetSetting functions to save and retrieve information from the registry, these functions only operate on a specific section of the registry, the Visual Basic and VBA Program Settings of the HKEY_CURRENT_USER root key.
This article outlines the use of 32-bit Windows API functions, which can be used to set and retrieve values from anywhere in the registry. The topics and function references in this article can be generalized to program the 16-bit registry.
The 32-bit API functions also include support for security, although an overview of security is outside the scope of this article.
NOTE: The SaveSetting and GetSetting functions are not part of the VBA function library. However, the sample code below still applies to 32-bit applications that implement VBA.
General Registry InformationThe 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 LocationAfter 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.
With this procedure a call of:
will create a key called TestKey immediately under HKEY_LOCAL_MACHINE.
Calling CreateNewKey like this:
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.
A call of:
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.
With this procedure, a call of:
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'.
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
SetValueEx and QueryValueEx Wrapper Functions:
Programming the Windows 95 User Interface, Chapter 10 - "Using the Registry"
For function references: Any guide to the Win16 or Win32 API.
Article ID: 145679 - Last Review: July 15, 2004 - Revision: 1.2