传递简单变量 ByRef 和 ByVal

传递 ByRef 或 ByVal 表示参数的实际值是否通过 CallingProcedure 传递给 CalledProcedure，或者是否将参考（在某些其他语言中称为指针）传递给 CalledProcedure。

如果参数传递给 ByRef，则参数的内存地址将传递给 CalledProcedure，并且 CalledProcedure 对该参数的任何修改都将转换为 CallingProcedure 中的值。

如果参数传递给 ByVal，则实际值（而不是对变量的引用）将传递给 CalledProcedure。

一个简单的例子将清楚说明这一点：

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 Sub

另一个例子：

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