How to validate an IBAN code with VB/A

Bank accounts are identified with a standardized IBAN code that simplifies international transactions. The code identifies the country, the banking institution and a customer account. You’ll find a function to validate an international Bank account IBAN identifier with VB/A in this post, along with a bunch of test IBANs.

There’s a “checksum” contained in the IBAN, that can be validated using a modulo 97 algorithm. You can peek here for a detailed explanation of the validation: I borrowed the modulo 97 algorithm from some code I found online, and wapped it at my sauce.

The encoding standard in Switzerland has its peculiarities; it has a length of 21 characters and the Bank ID is composed of only number digits. Same rules seems to apply for Lichtenstein (

You will need these small support functions too. IsOnlyNumbers() will return True if a text is composed only of digit characters “0” to “9”, and IsAlphaNum() will return True if the text is composed either of digits or letters “A” to “Z” in UPPER case only.

Here’s a piece of code to test the function, with a bunch of IBANs I gathered online:

Public domain. Enjoy !

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How to reverse a string in VB/A

There are many ways to do a simple string inversion, character by character, with VB/A. This function uses the Mid$ keyword as a function and as a statement to do it.

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Solving the Unicode, UTF8, UTF16 and Text Files conundrum in VBA

Understanding Unicode variants like UTF8 and UTF16 and how they impact your Office VBA development is not so straightforward. This post will guide thru the experience of reading a text file with VBA, explain some of the pitfalls you may encounter on this path when dealing with different text encodings and file formats. We’ll shed some light on essential Unicode concepts you’ve preferred to leave aside until now, because – let’s face it – who wants to spend hours reading wikipedia or MSDN just to read a text file or understand the many rules and APIs for converting between encodings ?

No bulky and verbose .NET or undecipherable C++ code complications here.
Just immediately actionable, simple and humble, VBA code with one function to rule them all, and a 10 to 15 minutes read to understand it all.

Let’s start the experience right now. Try something:

  • Open Windows notepad and copy/paste (or type) this text:

    Fancy a café ? Or a piña colada ? – Oh, that’s so cliché!

    I have a strong impression of Déjà vu.

    You hide your true motive behind a friendly façade.

    (Just my lame try to compose words with diacritics, in english. Inspiration found here and here)

  • Save the file; let’s say in c:\temp\textfiles\notepad_text.txt

Now we’ll try to read it and display it in Visual Basic, line by line, as usual:

Executing the “Test_ReadTextFileByLine” Sub (in the debug window) from this simple code snippet should do it…

…or not (!). The accented characters don’t display correctly.

Unicode, UTF8 and UTF16

Let’s state some facts before banging our heads on that:

  • Two forms of Unicode will be of interest here: UTF8 and UTF16.
  • “Windows is Unicode“, UTF16 Unicode. So is VBA. Unicode is a big character set which is meant to be able to represent the character glyphs of different languages.
  • Unicode (UTF16) encodes a character with two bytes (a “wide” character, in extension “wide” strings).
    (Note: UCS2 is history, assume UCS2 (or UCS-2) is UTF16)
  • The representation of a character in Unicode is also called a code point.
  • UTF8: not all the characters in the Unicode character set really need two bytes of encoding. UTF8 is sort of a packed representation of a series of Unicode characters, where one or two bytes can be used to represent a wide character.

Back to reading our file

At this point, we can guess that our Notepad old friend (on Windows 10 en_US version in my setup), probably stored our text file using a UTF8 encoding, which VBA is not aware of. Let’s take a look at the bytes in the file:

We see at lines 0 and 30 that our accented “é” are encoded as the two bytes C3 and A9, so this is a UTF8 file.

Then, at some point, we’ll have to convert an UTF8 representation of string to a UTF16 VBA friendly one.

Unfortunately, VBA cannot help here, so let’s take a detour to our trustworthy Win32 API.

Converting from UTF8 to UTF16 with the Win32 API

You’ll find all the code in the demo database of my reading_text_files github repository.

The function we’ll need is MultiByteToWideChar(), which we can declare as:

We’re going to have two variable sources, byte arrays and strings, to convert to UTF16, this is the VBA API functions signatures we’ll use:

Unicode normalization

There’s more than one way to represent a combination of characters in Unicode (MSDN). Extract:

Capital A with dieresis (umlaut) can be represented either as a single Unicode code point “Ä” (U+00C4) or the combination of Capital A and the combining Dieresis character (“A” + “¨”, that is, U+0041 U+0308). Similar considerations apply for many other characters with diacritic marks.

Simply put, a problem rises if we compare two Unicode strings that conceptually are the same, but use different code points (as the example above).

There are two more Win32 API functions that can help with that. One, NormalizeString(), transforms a Unicode string to a standard form, so it can be compared with another, even if the representations are different. The other, IsNormalizedString(), tests if a Unicode string is in the expected form.

There are a number of standard forms, but mainly, the one that “compresses” the code points into one character (I mean we get the attached form of “ae” instead of the “a” and “e”) is “NormalizationC”, value 1, from the following (C++) enumeration:

Normalization is an optional step, but for security considerations, should be used.
I wrapped the API (and followed MSDN guidance) in these two VBA API functions, and two others to get any error information:


I’m not following my coding guidelines for keeping error information inside a module, because we get an error either when calling Win32 API functions or a “logical” error when using the VBA API.

Then to test if something went wrong when calling UcNormalizeString() we have to test like that:

You can see a test scenario, that I sort of translated from the ones in MSDN, in the Test_Normalization() Sub, which calls:

Back to reading our file – again

Ok, now we know for sure that our file is in UTF8.
And we know that we have a nice UTF8DecodeString() at our disposal.

Are we not tempted to make this slight adaptation to our ReadTextFileByLine() function ? (see the UTF8DecodeString call in this code):

The result:

Whaaaat ? – Let’s debug that using the provided DumpStringBytes() function:

Which brings us to that output:

As we can see (and compare with the previous file’s hex dump), we do not have an UTF8 string in the variable sLine that is read by VBA from the file.

VBA converts the line it read from the file to a double byte (UTF16) string.

We cannot use VBA to read an UTF8 encoded text file using string variables.

Solution for reading and converting an UTF8 text file

We have to open the file in binary mode and read the contents in a byte array. This way VBA doesn’t do any conversion. We then just convert the byte array to an UTF8 string with the UTF8DecodeByteArrayToString().

And finally, we get it right:

Other text file encodings and BOMs

If Notepad saves files in UTF8 encoding, there are other encodings of text and file formats.

UTF8 and UTF16 text files may have, or not, a special series of bytes at the start of the file called the BOM (Byte Order Mark). The BOM is a magic number that we can use to infer the file encoding and byte endianness (order of bytes) of the file contents.

Without the BOM, guessing the file encoding can be tough.
But when there’s one, we can use it to make the necessary conversions, like in the following GetFileText() function, that can handle the following file encodings:

  • UTF16 BE / LE (Big Endian / Little Endian) with or without BOM,
  • UTF8 with or without BOM
  • ANSI (8 bits characters text, different character sets or code pages possible)

This is the signature of the function (code in the MTextFiles module of the Reading_Text_Files.accdb project), with a bit of documentation:

There’s a “text_files_samples” directory, in the github repository, with one file for each possible text file encoding.
Note that there are no UTF16 files with no BOM, as I used Notepad++ to generate the files and there’s no option in Notepad++ to generate UTF16 files with no BOM.

The Test_ReadSampleEncodings() procedure will read and check the contents of each file with this GetFileText() function:


We’ve seen different representation of text and encodings like UTF8, UTF16. We’re now able to convert between those encodings. And we now know how to read text from files with some of the most common file formats we may encounter, with VBA.

From here, it should be quite easy to also write any of these formats (using files open in binary mode helps).


Head to the Reading_Text_Files github repository to get the source code, the example files and the Access demo database.

(MIT Licence)

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Localization demo application screenshot

Using national language support in Office with VBA

If you need to handle multiple languages, get some specific regional settings, or do things like implement dynamic runtime language switching in your Microsoft Office solutions, you can leverage some additional help using the national language support Win32 API in VBA.

Do you know why you have to use the US English date format when you assign a date literal to a variable in VBA or in a SQL statement, surrounding it with “#” characters (like in: MyDate = #1/6/2020# for the 6 jan. 2020) ?
That’s because VBA (and the Office Object Model) is internally language locked on the locale which language ID is #1033.

What’s a locale and a language ID ? That’s how Windows manages multi language support.

There’s a lot of information about that on MSDN and on the web. Too much in fact to get started quickly.

This post will try to help you spare some time, make that journey quick and easy and jump into action now.

Here you’ll find :

  • A short review of the key concepts regarding national language support in Windows. Just what you need to know. Like what that means, and what language IDs and locales are.

  • A VBA standard module wrapping some of the most useful NLS Windows API immediately actionable.

  • A Microsoft Access database demo application using the module.
    See the short demo video:

Localization with VBA and the Win32 API demo

National language support with the Windows API

From MSDN:

The National Language Support (NLS) functions help applications support the different language- and locale-specific needs of users around the world.

The National Language Support (NLS) functions permit applications to:

  • Set the locale for the user
  • Identify the language in which the user works
  • Retrieve strings representing times, dates, and other information formatted correctly for the specified language and locale

Locales and Languages

Here’s the short version, while the full version of this topic is on MSDN.

  • In Windows, each language is identified by a 32bits Long value, the LANGUAGE ID, which has two parts:

    • The lower 16bits are the PRIMARY LANGUAGE ID
    • The higher 16bits are the SUB LANGUAGE ID

    Each language id can be translated to a string. For example, 1033 is “en_US” and 4108 is “fr_CH”. “en” is for the PRIMARY LANGUAGE ID, and “US” for the region, is the SUB LANGUAGE ID.

  • Each LANGUAGE ID has an associated LOCALE

    A “locale” is a collection of language-related user preference information represented as a list of values

  • Each value in the locale list, is indexed by (ie accessible via) a 32bits Long value, the LOCALE ID.

  • There can be multiple locales associated with one (primary) language (“en_US”, “en_GB”, etc…).

  • By using a valid LANGUAGE ID, applications can get localized strings and regional settings, like the full or abbreviated names of days and months, the region currency name and symbol, the various date and time formats, etc…

  • There is a preinstalled set of languages (and their locale settings) that ships with Windows.

    • LANG_SYSTEM_DEFAULT is a predefined constant for the language ID used to install WIndows. SUBLANG_SYS_DEFAULT represents its sub language ID.
    • LOCALE_USER_DEFAULT is a predefined constant for the language ID set for the current user.
    • There’s a predefined set of constants (LANG_*) for PRIMARY LANGUAGE IDs.
    • There’s a predefined set of constants (SUBLANG_*) for SUB LANGUAGE IDs.

Microsoft Office Application object language settings

Each VBA project in an Office application has access to a global Application object that has a:

  • LanguageSettings member that will give us a set of language IDs (MsoAppLanguageID enumeration), among which we can distinguish:

    • The language ID used to install Office (msoLanguageIDInstall),
    • The language ID in use for the current application (msoLanguageIDUI)
  • LanguagePreferredForEditing() function, that returns True, if a given language ID is used for editing (however that applies to the application).

Example (demo database)

Localization_win32.accdb, in this github repository, is an Access Database that illustrates how we can retrieve these language and regional settings from VBA.

It contains the MIntl.bas standard Visual Basic module, that wraps the necessary Win32 API functions and declarations. It also provides shortcut functions for some frequently used settings.

More on globalization

Globalization Documentation portal on MSDN.


The files of this project are in the github repository, including the demo database (MIT license).

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Explaining the real time device detector Access demo database

In this post, we’ll examine and explain how the Access application that demonstrates a possible, real life use case, of the device detection feature of the AxDeviceDetector ActiveX server.

See the downloads section below to download a copy of the database.


We want to allow, let’s say, restaurant waiters or employees, to register their shifts by typing in their password, clicking a (start or end) button, and then plugging a USB key into the computer, to confirm they are who they say to be. This is an instance of a multi factor authentication, or MFA, system.

The DeviceDetectorAuthDemo.accdb demo database is essentially a finite state machine implementation.

Using USB device for multifactor authentication demo

States and transitions

The frmMain form can be in one of these 4 states:

  1. Select employee
  2. Enter password
  3. Wait for action
  4. Wait for device detection

It’s a cycle, when the wait for the device detection ends, we return on the first state (Select employee).

There is a constant definition for each of these states:

When placed in one of these states, the form needs to update its UI, so only the next possible state(s) can be triggered. This is done in the EnableStepControls() method. This method also updates the UI to show in which state number it is, by moving a green square (it’s a label control) under the correct state number label.

State transition triggers

There are two classes of events that provoke the transition between these states:

  • UI elements actions

    • Double-click on the employee listbox
    • Button clicks
  • Timer event

Each event code that provokes a state transition has the responsibility to do so only if the UI holds valid values for every possible event parameters. In this simple demo, cmdOK_Click() is a good example:

To change state, DisableCurrentStep() and ActivateStep() are called in sequence.
DisableCurrentStep() executes whatever code is needed, before the state transition occurs:

ActivateStep() executes whatever code needed, before the new state is reached:

By design, there is a parameter for the transition to state 4 (Wait for device detection): the action code, which is one of these possible values defined as constants:

This way, when the device arrival/removal event sent by the AxDeviceDetector ActiveX server arrives, we know what action to take. The action code is stored in the miAction form scoped variable. Here an example, in the code executed when we click on the cmdRegisterDevice() button:

In the moDetector_OnDeviceArrival() there is a “Select Case miAction” statement that can now execute the correct action and transition back to step (ie state) #1 (select employee).

A class of state transitions is missing

Guessed which one ? – If not, then try to select another employee while you’re in state #3. You can’t.

There are at least two “cancel” actions that are missing:

  • A “cancel” button is missing, along the “OK” button
  • Another “cancel” button is missing if we want to cancel the wait for the device arrival.

Both of the action could for instance simply return us to state #1. I’ll let that for you.

About hashing

To link the USB device to an Employee, we generate a simple hash with the password, the device product id and the device serial number. That is discriminating enough to make it reasonably difficult to reverse engineer:

I’ve used here one of the first MD5 functions for VBA I googled for. You can replace that with a SHA256 to make it stronger, and add your additional parameters to generate the hash.

You should however avoid displaying and/or logging too much information, as I do for the sake of the demo, like the device product id, in a production application.

Avoiding blocking UI while handling ActiveX server events

We should avoid displaying any blocking UI elements like message boxes, input boxes or modal dialog boxes. This would prevent the server from notifying us of further events while those UI elements block the application’s VBA thread. The ActiveX server itself runs on another process/thread, so it will not block or crash. It has room for buffering 50 messages, that’s its event queue default size. When the server event queue becomes full, it’s emptied and the cleared events are lost.

About the Employee table

  • We have to store the device serial number (field AuthDeviceSerial), if we want to avoid registering an already registered device to another user;
  • The EventLog table is just here for the demo. You may want to (re)use your own logging system.
  • You should of course split your database, ie do not keep the data tables in the same database as the application, but rather link them.

That’s it !


All the material including the DeviceDetectorAuthDemo.accdb database, is available in my AxDeviceDetector github project


Credits: Post photo by Kentaro Toma on Unsplash

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Explaining how to detect device arrival/removal in an ActiveX server in real time

We’ve seen know how to get some useful information (like vendor ID and serial number) from attached Windows devices, using a C DLL. Interfacing the DLL with Visual Basic, was then just a matter of declaring the DLL functions in a standard module. With some more basic wrapping, we’ve obtained a simple API function and a data structure, to query for device information in Access.

Reacting to real time device arrival/removal notifications in VB/A

Getting notified in real time (well, as near as that as we can get, at least), when a USB device is plugged or unplugged from the system is the next step. This will allow us later to do things like build an Access application that can use a USB device as a multifactor authentication device (MFA).

Receiving notifications about device arrival or removal in windows is achieved by registering for that, via the RegisterDeviceNotification() Win32 API function. By then listening for the WM_DEVICECHANGE windows message, we can react accordingly.


VB/A cannot listen for windows messages on its own. We have to use a “subclassing” technique, where we redirect all the messages Windows sends to a VB Form (which itself is a window), to a custom routine. I use a subclassing technique derived from “Sensei” Bruce McKinney’s “Hardcore VB 5” book (free link), where we end up responding to the Windows messages we choose by implementing an ISubclass interface, in a Visual Basic Form. Here’s the snippet in frmMain that handles what we need:

Building an out-of-process ActiveX exe server

An ActiveX out-of-process server written in (classic) Visual Basic, is an independent 32 bits executable that serves objects running on their own threads, in an external process. In VBA hosts like Access or Excel, the Visual Basic code runs in a single thread of execution, so it cannot handle simultaneously the tasks of continuously responding to Windows messages and running the VBA application. I already explained why it would be a bad idea to use subclassing techniques in a VBA host application, talking about how to detect Windows session lock/unlock in VBA.

Object classes that are exposed by an ActiveX OOP server have the additional advantage of being accessible in 32 and 64 bits VBA hosts, thanks to (automatic) COM inter process communication marshalling.

I’ve used this technique in the three ActiveX servers I’m presenting on this series on my blog:

  • AxSessionLockDetector

    • Provides classes and events to detect and react when a user locks or unlocks his/her Windows session.
  • AxDeviceDetector

    • Provides classes and events to detect then there’s a device (or media) arrival or removal from the system (The one we’re discussing here).
  • AxHttpSrv

    • Provides classes and events to implement an HTTP web server in Microsoft Access.
    • Although this is the last one of this series, it is the oldest (I wrote it back in 2011), and it served as a base template for the two others.

However, when writing the ActiveX server we’re discussing here, I ran into a quite unexpected problem.

While trying to raise events or invoking OLE callbacks to notify the host for events, automation errors where popping up, instead of raising events (or executing OLE callbacks), basically rendering the solution useless. The first actionable information I found about that by googling around is in this KB article, located in a quite interesting github repository (it’s a static repository of Microsoft knowledge base articles).

A nice workaround consists in queuing the Windows messages we receive in the function implementing the ISubclass interface, and notifying them a bit later, using a timer to pop them back from the queue.

So, I quickly added a fixed size queue, stored in a circular memory array, specializing the CQueue class I presented in an earlier article where I was illustrating how a circular queue implementation works.

Strangely, I did not have to use this queue/timer technique for the two other ActiveX EXE server, but, alas, I can’t explain why is the difference between all of them.

Events or OLE callbacks ?

For an ActiveX server (or DLL for that matter), we can use two techniques to notify an object instance owner:

  • Events

    • Technically, they’re disguised OLE callbacks. You first declare the event in a class definition module, then raise the event with the RaiseEvent VB keyword;
  • OLE Callbacks

    • The client process has to give a reference to an (untyped) Object, to the ActiveX server class, that will keep a reference on it.
    • The ActiveX server class then tries a late bound call on a specific method name on the object reference, that’s the late bound call or OLE callback.
    • One key difference with raising events is that you control the callback sequence in the ActiveX server, when you chain multiple OLE callbacks; when you raise events, you can’t control in what sequence the client receives them.

The DeviceDetector class in the AxDeviceDetector ActiveX server allows for both methods to be used. For each of the two methods, you also have the option of passing parameters to the event procedures or OLE callbacks or not. If not, then the client can call methods on the class to get them. This is commented in the class source code:



You should see a schema illustrating a bit more nicely how this ActiveX Server works, as the image of this post.
Head to the github repository to download all the related material.

In the next post, we’ll see a real life possible use case for this ActiveX server.
I’ll explain the Access Demo application that you can see here in the mean time:

Using USB device for multifactor authentication demo


Browse the source code for more specific comments and explanations.

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How to get useful Windows device information in VBA

Here are (at least) 3 properties of hardware like hard disks (whether they are HDD, SSD, USB or else), printers or anything else that Windows considers a device. These can be very useful to obtain in applications that manage enterprise assets like data and documents:

  • Vendor name,
  • Vendor ID,
  • and serial number.

These hardware properties allow us to uniquely an reliably identify a physical device.

Unfortunately, they’re not so easy to obtain. Particularly if we develop our applications with the “high level” languages that we use in database management systems like Microsoft Access (but also WinDev or FileMaker to name a few others), or in development environments that do not have the necessary, production ready, components or libraries to interact with the system.

Then there are different technologies we can use to get to these hardware properties, like:

  • Windows Management Instrumentation (or WMI), which has already morphed into MI; it is feature rich and COM/ActiveX friendly, but – boy – what a learning curve and a maintenance nightmare threat that would be, just do such a simple thing;
  • .NET, although it would be like using a cannon to kill a mosquito to fire up the .NET runtime engine just to use a nugget of its capacities to bring this small functionality to applications that are not .NET based.
  • The venerable and almighty Win32 API, that we’ll use here from C, to bridge its functionality to Visual Basic, because the Win32 API is mostly C/C++ friendly; my winner here, attaboy.

So, let’s start at the end (!), because we want to get into action immediately, don’t we ?
Some explanation will follow later in this post.

Just before jumping there, let me point out where I am going with all this stuff next:

  • We’re going to combine this code in an out of process, Visual Basic 5 ActiveX EXE server. That will allow us to detect when a USB (or other device type) is plugged or unplugged into the system, in real time;

  • That’s for a bit later, we have some other things to talk about first, but I can’t resist the urge to spoil it:
    using a similar technique (the ActiveX OOP EXE server), we’ll turn Access into a (local machine/network) Web server (whaaat ?!? – Yes, no apache, nginx, node, or whatever needed!)

Watch the (short) demo video

Get device information from an access database demo


  • binaries

    • deviceinfo.dll (32bits version, MD5 sum: fb86ea314cdc4b2fd42f01b3876230d3)
    • deviceinfo64.dll (64bits version, MD5 sum: c27ce08c1c7d982bc475181d6f1cc613)
  • C DLL source code on my github

  • Access Demo database

    • deviceinfo_dll.accdb (contains the MDeviceInfo.bas module with the necessary declares, and additional wrapping to easily use the DLL with one function call and a supporting Type definition).
      Important note: copy the two DLLs (deviceinfo.dll and deviceinfo64.dll) in the same directory where you put the demo database deviceinfo_dll.accdb. The DLLs have to be in one of your PATH directories, or in the same directory of the application using them.

Some (quick) explanation

We can see the VB/A declarations that import the DLL functions in the declarations section of the MDeviceInfo.bas module:

Get to one API function

Instead of crippling our code with calls to each of the DLL functions, we can create one single function that does it all:

This way, we don’t have to worry about forgetting to call the DICreateDeviceInfo() and DIDestroyDeviceInfo() functions that are necessary for the DLL to do its job without crashes.

We gather the retrieved device information in an easy to access structure, in the following (public) Type definition:

Another way of doing it is using a class module. We’ll do that in the next post, where we set up the ActiveX OOP EXE server that will notify us of the devices arrival/removal in real time.

Sample usage

Take a look at the demo() procedure in the MMain.bas module:

About commercial use

If you’re following me thru this coding journey in my latest posts, you’ve probably noticed that I’m putting out all of the code and other assets under either the MIT or the GPL v2 licenses. While the works under the MIT license are completely free to use in all scenarios (commercial or not), that’s not true for works under the GPL v2 license, where you have to give these assets or your derived ones back to the community or whomever you distribute it.

Talking about the journey, if you’re wondering why I’m starting to making code and posts rain in these days (well, I mean, considering my personal publishing scale), allow me to give you a hint: I’ve started my sole ownership company as an independent software developer, back in may 1995…

So, I’m however going to set up a dual licensing system, so you can reuse the code/assets I publish here (or thru, in your commercial applications without worries. I know one buck has not the same value depending on our situation or where we live. Fear not, I can’t make specific promises for now, but I’ll do my best to be fair and affordable for everyone, leaving open the option to paypal me for a coffee or a beer, or just leave a donation (on which I’ll give back somehow), when it is reasonable.

Anyway, if you made it thru here, thank for your attention, don’t hesitate to share a link to this post where you see fit, open or join the conversation here, or drop me a tweet (I’m @francescofoti), I’ll always appreciate that.

And see you soon, because we’re not done yet 😉

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How to detect windows session lock/unlock in VBA

There are (at least) 3 solutions to detect when a user locks his/her workstation on Windows and react on the event.

  • A light and efficient solution using Classic Visual Basic (here VB5).
  • A very bad solution in VBA, which involves subclassing and using the Windows API directly.
  • An hybrid solution for an Access (VBA) application, which uses an out of process 32bits ActiveX EXE server written in Classic Visual Basic (VB5), that’ll work with 32 and 64bits VBA versions.

I’m trying not to use C (or any other language/tool) to write a DLL, although that would be also easily possible.

The windows API function that allows us to be notified when a user session is locked or unlocked (among other notifications) is the WTSRegisterSessionNotification() function.

Solution 1: The Classic Visual Basic 5 solution

We generate a simple 32bits standalone EXE application:

Get the binaries:

SessionLockDetector.exe (13.5 K, MD5: 57f23cb31c6f9ccd2a35c52384b90ff5)
If you need the VB5 runtime DLL (should already be present on XP up), download it here, unzip it and drop it in the same directory as the SessionLockDetector.EXE (.zip MD5: 7f32b01c04b0208ac917d7e266eb6709, extracted .dll MD5: eac679185ad621eeace9b6b286372f27).

Get the source code: SessionLockDetector (standalone) Visual Basic 5 project.

This task in quite easy in VB5 and it is also nicely stable. We just have to subclass the Form to be able to receive and handle the windows messages sent by the system.

Solution 2: The (very) bad solution

You might be tempted, as I did, to simply jump into a new Access database and apply the same technique. Just add the standard and class modules from the vb5 project, and subclass an Access Form like we did for the VB5 Form.

But Access is a different beast than vb5.

Subclassing the Form (in VBA) will make Access quite irresponsive at some point, because the subclassed form will throw a lot of messages in the WindowProc hooked into the (single threaded) VBA interpreter. Access will enter an almost unbreakable loop trying to keep up handling the event cascade while also trying to do its own work (you will see the VBA IDE window title bar endlessly update its text, if you try to run the sample database; but don’t do it please, take my word for it). At this point, even Windows itself (the desktop explorer process) will become frighteningly irresponsive. So take at look at this database code if you’re curious, but, once again, DO NOT EXECUTE / OPEN the “frmMain” form it contains (open in design mode only, don’t double-click it).

You’ve been warned. Download the very bad database that you shouldn’t open, at your own risk.

Solution 3: The hybrid solution

This is where we build an ActiveX EXE server with the same VB5 code that we used in the first solution, but we wrap the functionality inside an automation class. This will be the “LockUnlockDetector” class (which fully qualified with the name of the ActiveX server is “SessionLockDetector.LockUnlockDetector”), that will throw just two events, one for when the session was locked (OnSessionLock), and the other when it unlocks (OnSessionUnlock).

Building the VB5 ActiveX EXE server

Here’s the code of the LockUnlockDetector class module (VB5, 32bits):

By the way, according to the coding guidelines published here, we’re creating a class which will be made available outside of the VB project (that’s the goal), so we do not use any prefix before the class name (no “C” preceding the name).

To create an ActiveX EXE server, we set the properties of the project like that:

Now every object instance of class LockUnlockDetector will run in its own thread, and as this thread is in the EXE, it runs in the background and isolates the host (Access) from any problem occurring in the EXE.

Best of all, even if the EXE is 32bits, thanks to the beautiful architecture of COM (ie. ActiveX), cross platform calls are transparently marshalled and a 64bits Access VBA host can also use these 32bits automation classes.

The only disadvantage of this solution, is that we have to register the EXE server on the target machine.
In order to do that, we open an console window in administrator mode, navigate to the directory where the compiled EXE server is, and run it. This will silently write the required windows registry entries, and we’ll see the automation server appear in the Project References dialog of the VBA IDE in Access.

To use the detector class in Access, we then add the reference to our project:

Then we create a form (named frmMain here), and we just need this code:

Then we can respond to Lock/Unlock events as we wish:

In the provided sample Access database I added an history table to store the events, that’s what the AddHistoryRecord function does:


AxSessionLockDetector.EXE – ActiveX EXE server binary (if you’re missing MSVBVM50.dll see the above download link in solution 1).
SessionLockDetector – VB5 ActiveX EXE server project and source code.
SessionLockDetector.accdb sample database using the EXE server (remember to register the SessionLockDetector ActiveX server (AxSessionLockDetector.exe) binary by running it once with administrator privileges).


  • You can extend the functionality of the ActiveX EXE server to be notified for other events supported by the WTSRegisterSessionNotification windows API, and raise appropriate events. You can write a windows service that directly uses the server or transform solution 1 to be a windows service.
  • You can also modify solution 1 to be notified for other supported events and take any action you need, like running a batch file.
  • You can use the hybrid solution in your Access projects to be able to do smart things like freeing database or resource locks once a user locks its workstation.

MIT Licence

Copyright © 2019, Francesco Foti,
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. The Software is provided “as is”, without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. In no event shall the authors or copyright holders (Francesco Foti) be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the Software. Except as contained in this notice, the name of Francesco Foti or shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from Francesco Foti.

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How to implement a circular queue in VBA (Excel)

Animated view of the class in action

Temporal modules

Queues are part of the “temporal modules” family, with stacks and general double ended queues. They are containers that follow the FIFO (first in, first out) principle for storing and retrieving elements. While stacks follow the LIFO (last in, first out) principle, and general double ended queues can store and retrieve elements in both ways.

These temporal modules can be implemented in many ways, using for instance fixed or dynamic memory arrays, or linked linked lists.

This is a sample implementation of a queue in a fixed size memory “circular” memory array, in a VBA class module.

“Circular” meaning that we use a fixed size array to store queue elements (in this case strings), and as we push (QPush) an pop (QPop) elements in the queue, we use “pointers” (“qfront”, “qback”) to keep track of where the queue head and tail elements are in the array. “Pointers” being in this case array element indices of the (fixed size) memory array.

Download this Excel workbook here. (MD5 checksum: 46de8d5d18a25c02dbcff7dac9dc88ee)

Please note that this is a workbook containing macros (.xlsm), you’ll have to allow them to execute when opening the document.

About this implementation

The queue itself is implemented in the “CQueue” class module.

We create a queue with the (spoiler) “CreateQueue” method, which takes the maximum number of elements we can store in the queue, as a parameter. Here’s the function signature:

To be able to show the inner workings of the module in the Excel worksheet, I had to expose (as Friend) some methods that should remain private in a final implementation; they are wrapped in a conditional compilation directive, testing on the “USE_FOR_EXCEL_DEMO” project conditional compilation argument that you’ll find defined in the project properties (from the VBA editor, menu tools, entry project properties):

From here

  • We can change the type of the array to store something else than strings (variants, object references, integers, etc…). We could for instance use integers that would be array indices of another array where the data elements are stored.
  • We can persist the queue on disk quite easily, by writing the header information in a file, and then the queue elements. We a bit of more work, the queue can then be shared and accessed by different applications using simple file/region locking mechanisms of the operating system.
  • We could implement stacks and general double ended queues in the same way. We would have something like “Push” and “Pop” methods for a stack, and “RQPush”, “RQPop”, “LQPush”, “LQPop” for a general double ended queue.

The code presented here follows these coding guidelines. Enjoy 🙂

Copyright © 2019, Francesco Foti,
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. The Software is provided “as is”, without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. In no event shall the authors or copyright holders X be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the Software. Except as contained in this notice, the name of Francesco Foti or shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from Francesco Foti.

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Swiss Money Coins

How to round a number to a five cents multiple in VB/A

In switzerland, we like rounding monetary numbers to 2 decimal places, with multiples of 5 for the fractional part. This is (probably) because our (physical) money has no “cent” coins, but we have 5 cents coins. That’s commonly called “5 cents” rounding.


  • 1.6777777 becomes 1.70
  • 1.4444444 becomes 1.45
  • 1.0333333 becomes 1.05
and so on.

Years ago, I was “gifted” with the knowledge of a “magic” trick to achieve that.
And that’s how it was gifted to me:

multiply by 20, cut the integer part, compare to .5 to do the rounding, adding 1 if it equals or overflows .5, and finally divide by 20 for the result.
Pretty simple. It works. However, this may not be a so easy task to do in VB/A as it seems to be.

Here’s my version of this algorithm, in the form of my FiveCt() function.
Note that I do use Double to Currency type conversion in this code, it will also work with Single type values.

You can use this function in Excel or Access (or any VB/A) calculations, as in Access queries for example.


Round a double precision number to a five cents value.
Double in, Double out.

Notes and references on floating point variable types in VB/A

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