vb split 用法

vb split 用法
For i = 1 To AllNum1(LineNum1)
NumberNum1(LineNum1,i) = Split(Split(s,",")(i),",")(0)
Next i
尤其是Split(Split(s,",")(i),",")(0)怎么理解?特别是Split(Split(s,",")(i),",")后面的那个（0）什么意思啊?split函数后面加个（0）怎么理解,
我把代码发全一点,代码没问题,测试过了
Open PathIn1 For Input As #1
Do Until EOF(1) = True
Line Input #1,s
s = "," & s & ","
LineNum1 = LineNum1 + 1
Nnum = 0
For i = 1 To Len(s)
If Mid(s,i,1) = "," Then Nnum = Nnum + 1
Next i
AllNum1(LineNum1) = Nnum - 1
For i = 1 To AllNum1(LineNum1)
NumberNum1(LineNum1,i) = Split(Split(s,",")(i),",")(0)
Next i
Loop
Close #1