Understanding `ByRef` in Visual Basic

In both Visual Basic and Visual Basic .NET, the keyword ByRef is used to pass arguments by reference. This means the called procedure receives a reference to the original variable—not a copy—allowing the procedure to change the variable directly.

What Does `ByRef` Mean?

When a parameter is passed ByRef:

The procedure receives a reference to the actual variable.
Changes inside the procedure affect the original variable.
It allows a function to return multiple results by modifying variables.

Classic Visual Basic (VB6) Example


Private Sub ChangeNumber(ByRef x As Integer)
    x = x + 10
End Sub

Private Sub Command1_Click()
    Dim num As Integer
    num = 5
    Call ChangeNumber(num)
    MsgBox num   ' Shows 15
End Sub

Because x was passed by reference, modifying it inside the procedure also changes num.

VB.NET Example


Sub ChangeText(ByRef message As String)
    message = "Modified inside procedure"
End Sub

Sub Main()
    Dim txt As String = "Original text"
    ChangeText(txt)
    Console.WriteLine(txt)   ' Outputs: Modified inside procedure
End Sub

The original variable txt is changed because it was passed ByRef.

`ByRef` vs `ByVal`

Understanding the difference between ByVal and ByRef is essential for controlling how data flows in VB procedures.

Keyword	Meaning	Does the procedure modify the original variable?
`ByVal`	Passes a copy of the variable	No
`ByRef`	Passes a reference to the original variable	Yes

When Should You Use `ByRef`?

When you want a procedure to modify the caller’s variable.
When returning multiple values from a single function.
When performance matters and copying large structures would be expensive.
When interacting with certain APIs or legacy VB6 code that expects references.

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Understanding ByRef in Visual Basic

What Does ByRef Mean?