错误＆＃34;下标超出范围。＆＃34;关于VBA功能

Question

我的问题是，什么可能导致此错误（错误＆＃34;下标超出范围。＆＃34;）？我在VBA中运行一个函数，该函数从每分钟更新的特定CSV中读取数据。我的职责是：

Function CSVtoDataArray(CSVpath As String, fileName As String) As String()

Dim fnum As Integer
Dim whole_file As String
Dim lines As Variant
Dim one_line As Variant
Dim num_rows As Long
Dim the_array() As String
Dim file_path As String

whole_file = ""

file_path = CSVpath & fileName
' Load the file.
fnum = FreeFile
Open file_path For Input As fnum
whole_file = Input$(LOF(fnum), #fnum)
Close fnum

' Break the file into lines.'
lines = Split(whole_file, vbCrLf)
whole_file = ""
num_rows = UBound(lines)
the_array = Split(lines(num_rows - 1), ",")

CSVtoDataArray = the_array()

End Function

我的脚本开始运行后错误弹出一段时间，调试标记错误以到达这些行：

num_rows = UBound(lines)
the_array = Split(lines(num_rows - 1), ",")

这表明我的字符串whole_file为空，给num_rows的值为-1。为什么你认为是问题？为什么这个错误只在一段时间后发生而不是立即发生？