Microsoft KB Archive/105230
Article ID: 105230
Article Last Modified on 10/28/2003
- Microsoft Visual Basic 2.0 Standard Edition
- Microsoft Visual Basic 3.0 Professional Edition
This article was previously published under Q105230
When trying to use the Set keyword to assign a value to a formal parameter passed to a Visual Basic Sub or Function procedure, you may get a "Can't Set formal parameter" error at compile or run time.
Specifically, trying to use a Set statement on an object variable that is a formal parameter of a procedure results in this error.
This behavior is by design. You cannot use a procedure's formal parameter as the destination of a Set statement.
Object variables can be parameters of a Sub or Function procedure, but if an object variable is a parameter, its value cannot be changed inside the called procedure.
You can use a Set statement on an array of objects that is passed as a parameter. For example, you can modify the code shown in the "Steps to Reproduce Behavior" section to the following to prevent the error:
Sub Form_Load () ReDim X(0) As Form Call MySub1(X()) End Sub Sub MySub1 (FormalParameterX() As Form) Set FormalParameterX(0) = Form1 FormalParameterX(0).Caption = "Success" ' Form's caption will change. End Sub
If you make the object variable Global instead of passing it as a parameter, you can use Set statements inside procedures.
This behavior is by design.
Objects as parameters can be thought of as a copy of the structure that defines the object. If Set statements were allowed on these objects, this would change the value inside the routine, but upon returning from the routine the changes would be lost and the object variable would revert back to its original value.
Steps to Reproduce Behavior
- Start a new project in Visual Basic. Form1 is created by default.
Add the following code to the Form_Load procedure:
Sub Form_Load () Dim X As Form Call MySub1(X) End Sub Sub MySub1 (FormalParameterX As Form) Set FormalParameterX = Form1 ' Can't Set formal parameter error FormalParameterX.Caption = "Success" ' This is never executed. End Sub
- Attempt to run or compile the application to generate the "Can't Set formal parameter" error.
More Steps to Reproduce Behavior
Here is another set of steps that result in the error:
Start a new project in Visual Basic and add the following procedure to the application:
Sub s (tb As Table) Set tb = Nothing End Sub
- Press the F5 key to run the application. The error "Can't Set Formal Parameter" should occur immediately.
NOTE: Trying to force these objects to be passed by value by setting the ByVal keyword results in this error:
ByVal is allowed with the variable types listed in the error message, but it is not allowed with any other variable type.
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