先看看怎样应用：

'提取文件名全称(完整路径 As String)
'提取扩展名(文件名全称 As String)
'获取字符串字节数(字符串 As String)
'获取文件名称(文件名全称 As String)

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Private Sub Command20_Click()

Text1.Text = "从全路径名中提取文件名全称： " & 提取文件名全称("C:\AAA\BBB\CCC.exe")

Text2.Text = "从文件名全称中获取文件名（ABC.exe）: " & 获取文件名称("ABC.exe")

Text3.Text = "提取扩展名（CCC.exe）： " & 提取扩展名("CCC.exe")

Text4.Text = "获取字符串字节数(“钟点工”)： " & 获取字符串字节数("钟点工")

End Sub

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Function 提取文件名全称(完整路径 As String)
Dim X%, ct%

X% = InStr(完整路径, "\")
Do While X%
ct% = X%
X% = InStr(ct% + 1, 完整路径, "\")
Loop
If ct% > 0 Then 提取文件名全称 = Mid(完整路径, ct% + 1)

End Function

Public Function 提取扩展名(文件名全称 As String)
Dim I, J, PthPos, ExtPos As Integer

For I = Len(文件名全称) To 1 Step -1 ' Go from the Length of the 文件名全称, to the first character by 1.
If Mid(文件名全称, I, 1) = "." Then ' If the current position is '.' then...
ExtPos = I ' ...Change the ExtPos to the number.
For J = Len(文件名全称) To 1 Step -1 ' Do the Same...
If Mid(文件名全称, J, 1) = "\" Then ' ...but for '\'.
PthPos = J ' Change the PthPos to the number.
Exit For ' Since we found it, don't search any more.
End If
Next
Exit For ' Since we found it, don't search any more.
End If
Next

If PthPos > ExtPos Then
Exit Function ' No extension.
Else
If ExtPos = 0 Then Exit Function ' If there is not extension, then exit sub.
提取扩展名 = Mid(文件名全称, ExtPos + 1, Len(文件名全称) - ExtPos) 'Messagebox the Extension
End If

End Function
'使用：
'字符串变量 = 提取扩展名("c:\B_sys\Explorer.exe")

Function 获取字符串字节数(字符串 As String)
On Error Resume Next
Dim WINNT_CHINESE
WINNT_CHINESE = (Len("中国") = 2)

If WINNT_CHINESE Then
Dim l, T, C
Dim I
l = Len(字符串)
T = l

For I = 1 To l

C = Asc(Mid(字符串, I, 1))

If C < 0 Then C = C + 65536

If C > 255 Then
T = T + 1
End If

Next

获取字符串字节数 = T

Else

获取字符串字节数 = Len(字符串)

End If

If Err.Number <> 0 Then Err.Clear
End Function

Function 获取文件名称(文件名全称 As String)
Dim 扩展名 As String
扩展名 = 提取扩展名(文件名全称)
获取文件名称 = StrReverse(Mid(StrReverse(文件名全称), 获取字符串字节数(扩展名) + 2))
End Function