检查文件是否存在时出错53

Question

我使用以下代码检查文件是否存在：

If Len(Dir$(strFile)) > 0 Then

直到今天仍然有效。

在某些情况下，我收到以下错误：

错误指向上面的代码行。

我知道该文件不存在，但我不希望出现此错误。

Answer 1

我忘了提一下：文件名是动态的，取决于另一个过程。

我刚注意到，当错误发生时，另一个进程返回垃圾，导致大约2000个字符的长文件名。

我从未意识到文件名的长度有限制。

我创建了一个小项目来测试它，结果是上限是259个字符：

Option Explicit

Private Sub Command1_Click()
  Dim strFile As String
  Dim intLength As Integer
  strFile = App.Path & "\"
  intLength = 259 - Len(strFile)
  strFile = strFile & String(intLength, "a")
  If Len(Dir$(strFile)) = 0 Then
    MsgBox "file does not exist"
  End If
End Sub

使用值259可以正常工作，但260会出错。

Answer 2

我使用调用Windows API的函数来执行此操作。此函数处理空格和长文件名。

添加到声明部分：

Private Declare Function CloseHandle Lib "Kernel32" (ByVal hObject As Long) As Long
Private Declare Function CreateFile Lib "Kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, lpSecurityAttributes As SECURITY_ATTRIBUTES, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Any) As Long

Private Type SECURITY_ATTRIBUTES
    nLength As Long
    lpSecurityDescriptor As Long
    bInheritHandle As Long
End Type

Private Const OPEN_EXISTING = 3
Private Const FILE_SHARE_READ = &H1
Private Const GENERIC_READ = &H80000000
Private Const INVALID_HANDLE_VALUE = -1

实际功能

Function FileExists(ByVal fSpec As String) As Boolean
    Dim lngResult As Long
    Dim udtSA As SECURITY_ATTRIBUTES

    On Error GoTo errFileExists

    If Len(fSpec) > 0 Then
        udtSA.nLength = Len(udtSA)
        udtSA.bInheritHandle = 1&
        udtSA.lpSecurityDescriptor = 0&
        lngResult = CreateFile(fSpec, GENERIC_READ, FILE_SHARE_READ, udtSA, OPEN_EXISTING, 0&, 0&)
        If lngResult <> INVALID_HANDLE_VALUE Then
            Call CloseHandle(lngResult)
            FileExists = True
        Else
            Select Case Err.LastDllError  'some errors may indicate the file exists, but there was an error opening it
                Case Is = ERROR_SHARING_VIOLATION
                    FileExists = True

                Case Else
                    FileExists = False

            End Select
        End If
   End If

Exit Function

errFileExists:
    Err.Raise Err.Number, Err.Source, Err.Description, Err.HelpFile, Err.HelpContext

End Function