Visual Basic for Applications:
Logging

How to:

In VBA, there isn’t a built-in logging framework as found in some other languages. However, implementing a simple logging mechanism is straightforward. Below is an example of how to create a basic file logger.

1. Writing to a Log File: This example function, LogMessage, writes messages to a text file with a timestamp.

Sub LogMessage(message As String)
    Dim logFilePath As String
    Dim fileNum As Integer
    
    ' Specify the path of the log file
    logFilePath = ThisWorkbook.Path & "\log.txt"
    
    ' Get the next available file number
    fileNum = FreeFile()
    
    ' Open the file for appending
    Open logFilePath For Append As #fileNum
    
    ' Write the timestamp and the log message
    Print #fileNum, Now & ": " & message
    
    ' Close the file
    Close #fileNum
End Sub

To log a message, simply call LogMessage("Your message here"). This produces entries in log.txt like:

4/30/2023 3:45:32 PM: Your message here

2. Reading from a Log File: To read and display the contents of the log file:

Sub ReadLogFile()
    Dim logFilePath As String
    Dim fileContent As String
    Dim fileNum As Integer
    
    logFilePath = ThisWorkbook.Path & "\log.txt"
    fileNum = FreeFile()
    
    ' Open the file for reading
    Open logFilePath For Input As #fileNum
    
    ' Read the entire file content
    fileContent = Input(LOF(fileNum), fileNum)
    
    ' Close the file
    Close #fileNum
    
    ' Display the file content
    MsgBox fileContent
End Sub

Deep Dive

Logging in VBA, due to its lack of a native logging framework, is usually implemented through basic file operations or by harnessing the power of external COM objects for more advanced needs, such as logging to a database or interacting with Windows Event Log. Historically, logging in VBA has been a way to circumvent the limitations posed by its simplistic error handling and debugging tools. Although effective, direct file manipulation for logging is rudimentary and can be inefficient with large volumes of data or under high concurrency. For more sophisticated logging capabilities, programmers often turn to external libraries or integrate with systems specifically designed for logging, such as the ELK stack (Elasticsearch, Logstash, Kibana) or Splunk, through web service calls or intermediary databases. While VBA does not offer the modern conveniences found in newer programming languages, understanding its capabilities and limitations allows programmers to effectively utilize logging as a powerful tool for application monitoring and diagnostics.