vb 6.0 string 怎么实现 +=操作？

如题

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分步
VB code:
Dim a
Dim b
a = a + 1
a = a + b
'或者
'a = a + 1 + b

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哦,是string类型,走眼了。。。

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好像没有+=这样的操作符吧，
只能是
dim str1 as string , str2 as string
str1 = "**" str2 = "**"
str1 = str1 + str2

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VB不支持这个运行符
只能这样：strOne=strOne +strTwo
或者：strOne=strOne & strTwo
推荐后者，因为前者需要重载。

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举个例子:
VB code:
Private Sub Command3_Click()
Dim a As String, i As Long
Dim b(10) As String
b(0) = ""
b(1) = "hehe"
b(2) = ""
b(3) = "heihei"
b(4) = "lala"

For i = 0 To 10
a = a & IIf(a = "", IIf(b(i) = "", "", b(i)), IIf(b(i) = "", "", "," & b(i)))
Next
Debug.Print a
End Sub

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再问一个

    Set Fs_Start_Cmd_tcl = CreateObject("Scripting.FileSystemObject")
    Set F_Start_Cmd_tcl = Fs_Start_Cmd_tcl.OpenTextFile(F3, ForWriting, True, 0)

程序提示OpenTextFile 没有该函数或过程，为什么啊？

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c = a & b