.Net 下區(qū)別使用 ByRef/ByVal 的重要性

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

這些天在優(yōu)化程序時(shí)發(fā)現(xiàn) 當(dāng)傳送 大變量時(shí)，使用默認(rèn)方式（ByVal) 效率相當(dāng)?shù)?/p>

如傳入的參數(shù)變量類型 是 大字符串，數(shù)組，集合，DataSet 等

測(cè)試的關(guān)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(dāng)然，當(dāng)傳入得變量可以被修改或無其他作用時(shí)，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