Debug

The intrinsic debugging object. Writes to the IDE’s Debug Console, clears it, asserts a condition, and writes to the trace log.

Debug is a built-in class with a predeclared instance, so there is nothing to declare or construct — the name Debug is the object. It has four methods and no properties.

method	writes to
Print	the Debug Console
TracePrint	the active trace output
Cls	— clears the Debug Console
Assert	— halts if a condition is False

Debug.Print

Writes text to the Debug Console.

Syntax: Debug.Print [ outputlist ]

outputlist: optional Expressions to write. Separate them with a comma to start each at the next print zone — a fixed column every 14 characters, so zones begin at columns 0, 14, 28 and so on — or with a semicolon to place them immediately after one another. An expression longer than its zone pushes the next one into the zone after. A trailing semicolon holds the cursor on the same line, so the next Print continues it; without one, the line ends. With no outputlist at all, Print writes a blank line.

Debug.Print                       ' a blank line
Debug.Print "value: "; 42         ' value: 42
Debug.Print "left", "right"       ' right starts at column 14
Debug.Print "no newline yet";
Debug.Print " --- continued"

Numbers are written with a leading space where the sign would go, and a trailing space after the value, so Debug.Print 1, 2, 3 puts 1, 2 and 3 at columns 1, 15 and 29 rather than 0, 14 and 28.

Debug.TracePrint

Writes a message to the currently active trace output, not to the Debug Console.

Syntax: Debug.TracePrint [ outputlist ]

outputlist: optional Expressions to write, with the same comma and semicolon rules as Print.

Where the message goes is a project setting rather than a property of the call: Compilation: Trace Output selects the debug console or a file, and Compilation: Trace Flags selects what is traced. Tracing works in a compiled executable as well as under the IDE, which is the reason to prefer it over Print for anything you want to diagnose on a machine that has no IDE on it. See Debugging Features.

Public Sub ProcessOrder(ByVal orderId As Long)
    Debug.TracePrint "ProcessOrder called, orderId=" & CStr(orderId)
End Sub

Debug.Cls

Clears the Debug Console.

Syntax: Debug.Cls

This is the programmatic form of the console’s own Clear Debug Console button. Call it at the start of a run to separate that run’s output from the previous one.

Debug.Cls
Debug.Print "--- run starting ---"

Note

This is unrelated to the Cls method on a drawing surface such as Form or PictureBox, which clears graphics and text from that control rather than from the console.

Debug.Assert

Halts execution when a condition is False.

Syntax: Debug.Assert booleanexpression

booleanexpression: An expression evaluating to True or False. Execution continues when it is True and breaks when it is False.

Use it to state something the surrounding code relies on, so a violated assumption stops at the line that states it rather than further away.

Public Function Average(values() As Double) As Double
    Debug.Assert IsArrayInitialized(values)
    Dim i As Long, total As Double
    For i = LBound(values) To UBound(values)
        total = total + values(i)
    Next
    Average = total / (UBound(values) - LBound(values) + 1)
End Function

IsArrayInitialized is the right thing to assert here and UBound(values) >= LBound(values) is not: on an array the caller never sized, LBound and UBound raise error 9 themselves, so the assertion would be the line that fails rather than the line that catches it.