Understanding ByVal in Visual Basic

In Visual Basic and Visual Basic .NET, the keyword ByVal is used to pass arguments to a procedure by value. This means the procedure receives a copy of the variable, not the original variable itself.

What Does ByVal Mean?

When a parameter is passed ByVal:

• The called procedure gets its own copy of the variable’s value.
• Changing the parameter inside the procedure does not change the original variable.
• It is the default parameter-passing method in VB.NET.

Example in Classic Visual Basic (VB6)

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

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

The variable num remains 5 because the procedure changed only its local copy.

Example in VB.NET

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

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

Again, changing the parameter inside the procedure has no effect on the original variable.

ByVal vs ByRef

Visual Basic also supports ByRef, which passes the argument by reference instead of by value. A ByRef parameter allows a procedure to modify the caller’s variable directly.

Keyword	Meaning	Can the procedure change the original value?
ByVal	Passes a copy of the variable	No
ByRef	Passes the actual variable	Yes

Why Use ByVal?

• Prevents unintended changes to variables
• Makes functions more predictable
• Helps avoid side effects when debugging
• It is safer and generally preferred unless modification is intended

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