VBA Passing Arguments ByRef or ByVal
Passing Simple Variables ByRef And ByVal
Passing ByRef or ByVal indicates whether the actual value of an argument is passed to the CalledProcedure by the CallingProcedure, or whether a reference (called a pointer in some other languages) is passed to the CalledProcedure.
If an argument is passed ByRef, the memory address of the argument is passed to the CalledProcedure and any modification to that parameter by the CalledProcedure is made to the value in the CallingProcedure.
If an argument is passed ByVal, the actual value, not a reference to the variable, is passed to the CalledProcedure.
A simple example will illustrate this clearly:
Sub CalledProcedure(ByRef X As Long, ByVal Y As Long)
X = 321
Y = 654
End Sub
Sub CallingProcedure()
Dim A As Long
Dim B As Long
A = 123
B = 456
Debug.Print "BEFORE CALL => A: " & CStr(A), "B: " & CStr(B)
''Result : BEFORE CALL => A: 123 B: 456
CalledProcedure X:=A, Y:=B
Debug.Print "AFTER CALL = A: " & CStr(A), "B: " & CStr(B)
''Result : AFTER CALL => A: 321 B: 456
End SubAnother example:
Sub Main()
Dim IntVarByVal As Integer
Dim IntVarByRef As Integer
IntVarByVal = 5
IntVarByRef = 10
SubChangeArguments IntVarByVal, IntVarByRef '5 goes in as a "copy". 10 goes in as a reference
Debug.Print "IntVarByVal: " & IntVarByVal 'prints 5 (no change made by SubChangeArguments)
Debug.Print "IntVarByRef: " & IntVarByRef 'prints 99 (the variable was changed in
SubChangeArguments)
End Sub
Sub SubChangeArguments(ByVal ParameterByVal As Integer, ByRef ParameterByRef As Integer)
ParameterByVal = ParameterByVal + 2 ' 5 + 2 = 7 (changed only inside this Sub)
ParameterByRef = ParameterByRef + 89 ' 10 + 89 = 99 (changes the IntVarByRef itself - in the
Main Sub)
End Sub