而在 .Net(C#,VB.Net) 下， 參數默認是使用 ByVal （即按值傳送)  傳送的，一直沒怎么注意。

這些天在優化程序時發現 當傳送 大變量時，使用默認方式（ByVal) 效率相當低

如傳入的參數變量類型 是 大字符串，數組，集合，DataSet 等

測試的關鍵代碼如下,我傳入的字符串并沒有特別大，變量越大，使用 ByRef 效率越高,當然，當傳入得變量可以被修改或無其他作用時，可以改用 ByRef 傳

 Private Declare Function GetTickCount Lib "kernel32" () As Int32

    Private Function TestByRef(ByRef aa As String) As String
        aa = "1" & aa
        TestByRef = aa

    End Function

    Private Function TestByVal(ByVal aa As String) As String
        aa = "1" & aa
        TestByVal = aa

    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim teststr As String
        Dim Newstr As String

        Dim t As Int32
        Dim II As Int32

        teststr = "wosdfsdfdsfdsfsfdsfsfsfsfsfsfdsfdsfcvxcvxcvcxvvcxvvvxvcvxv"

        t = GetTickCount

        For II = 1 To 10000
            Newstr = TestByRef(teststr)
        Next

        MsgBox("ByRef  " & CStr(GetTickCount - t))

        t = GetTickCount

        For II = 1 To 10000
            Newstr = TestByVal(teststr)
        Next

        MsgBox("ByVal  " & CStr(GetTickCount - t))

    End Sub