FileAttr Function

Returns a Long representing the file mode for files opened using the Open statement, or the file attribute information for files, directories, or folders.

Syntax

FileAttr(filenumber, returntype)

Parameters

filenumber: Required. An Integer containing a valid file number of an open file.
returntype: Required. A Long indicating the type of information to return.
1: Returns a value indicating the file mode (Input, Output, Append, Binary, Random)
2: Returns the file handle used by the operating system

Return Value

Returns a Long value. The meaning depends on the returntype parameter:

When returntype = 1 (File Mode):

1: Input mode
2: Output mode
4: Random access mode
8: Append mode
32: Binary mode

When returntype = 2 (File Handle):

Returns the operating system file handle (an integer value used by the OS to identify the file).

Remarks

The FileAttr function returns information about files that have been opened using the Open statement. It provides two types of information: the file access mode or the operating system file handle. Important Characteristics: - File must be open before calling FileAttr - Error if file number is invalid or file is closed - returntype must be 1 or 2 - File mode values are mutually exclusive - File handle is OS-specific (Windows, Unix, etc.) - File handle can be used with API calls - Not applicable to files opened by other applications - Only works with files opened via VB6 Open statement

File Mode Values (returntype = 1)

Mode	Value	Description
Input	1	File opened for reading
Output	2	File opened for writing (new file or overwrite)
Random	4	File opened for random access
Append	8	File opened for appending
Binary	32	File opened in binary mode

Examples

Basic Usage - Check File Mode

Sub CheckFileMode()
    Dim fileNum As Integer
    Dim fileMode As Long
    fileNum = FreeFile
    Open "C:\data.txt" For Input As #fileNum
    ' Get file mode
    fileMode = FileAttr(fileNum, 1)
    Select Case fileMode
        Case 1
            Debug.Print "File opened for Input"
        Case 2
            Debug.Print "File opened for Output"
        Case 4
            Debug.Print "File opened for Random access"
        Case 8
            Debug.Print "File opened for Append"
        Case 32
            Debug.Print "File opened for Binary"
    End Select
    Close #fileNum
End Sub

Get File Handle

Sub GetFileHandle()
    Dim fileNum As Integer
    Dim fileHandle As Long
    fileNum = FreeFile
    Open "C:\temp.dat" For Binary As #fileNum
    ' Get operating system file handle
    fileHandle = FileAttr(fileNum, 2)
    Debug.Print "OS File Handle: " & fileHandle
    ' File handle can be used with Windows API calls
    ' Example: SetFilePointer, ReadFile, WriteFile, etc.
    Close #fileNum
End Sub

Verify File Is Open for Writing

Function CanWriteToFile(fileNum As Integer) As Boolean
    On Error GoTo ErrorHandler
    Dim fileMode As Long
    fileMode = FileAttr(fileNum, 1)
    ' Check if file is open for Output, Append, Random, or Binary
    CanWriteToFile = (fileMode = 2 Or fileMode = 8 Or fileMode = 4 Or fileMode = 32)
    Exit Function
ErrorHandler:
    CanWriteToFile = False
End Function

Common Patterns

File Mode Lookup Function

Function GetFileModeDescription(fileNum As Integer) As String
    On Error GoTo ErrorHandler
    Dim fileMode As Long
    fileMode = FileAttr(fileNum, 1)
    Select Case fileMode
        Case 1
            GetFileModeDescription = "Input"
        Case 2
            GetFileModeDescription = "Output"
        Case 4
            GetFileModeDescription = "Random"
        Case 8
            GetFileModeDescription = "Append"
        Case 32
            GetFileModeDescription = "Binary"
        Case Else
            GetFileModeDescription = "Unknown"
    End Select
    Exit Function
ErrorHandler:
    GetFileModeDescription = "Error: " & Err.Description
End Function

List All Open Files

Sub ListOpenFiles()
    Dim i As Integer
    Dim fileMode As Long
    Dim modeDesc As String
    Debug.Print "Open Files:"
    Debug.Print String(60, "-")
    Debug.Print "File#", "Mode", "Handle"
    Debug.Print String(60, "-")
    For i = 1 To 255
        On Error Resume Next
        fileMode = FileAttr(i, 1)
        If Err.Number = 0 Then
            ' File is open
            modeDesc = GetFileModeDescription(i)
            Debug.Print i, modeDesc, FileAttr(i, 2)
        End If
        Err.Clear
    Next i
End Sub

Safe File Operation Wrapper

Function WriteToFile(fileNum As Integer, data As String) As Boolean
    On Error GoTo ErrorHandler
    Dim fileMode As Long
    ' Verify file is open
    fileMode = FileAttr(fileNum, 1)
    ' Check if writable
    If fileMode <> 2 And fileMode <> 8 And fileMode <> 4 And fileMode <> 32 Then
        MsgBox "File is not open for writing", vbExclamation
        WriteToFile = False
        Exit Function
    End If
    ' Write data based on mode
    Select Case fileMode
        Case 2, 8  ' Output or Append
            Print #fileNum, data
        Case 4     ' Random
            Put #fileNum, , data
        Case 32    ' Binary
            Put #fileNum, , data
    End Select
    WriteToFile = True
    Exit Function
ErrorHandler:
    WriteToFile = False
End Function

Log File Access Information

Sub LogFileAccess(fileNum As Integer, logPath As String)
    Dim logNum As Integer
    Dim fileMode As Long
    Dim fileHandle As Long
    On Error Resume Next
    fileMode = FileAttr(fileNum, 1)
    fileHandle = FileAttr(fileNum, 2)
    If Err.Number = 0 Then
        logNum = FreeFile
        Open logPath For Append As #logNum
        Print #logNum, Format(Now, "yyyy-mm-dd hh:nn:ss") & " | " & _
                       "File#" & fileNum & " | " & _
                       "Mode: " & GetFileModeDescription(fileNum) & " | " & _
                       "Handle: " & fileHandle
        Close #logNum
    End If
End Sub

Check If File Number Is Valid

Function IsFileOpen(fileNum As Integer) As Boolean
    On Error Resume Next
    Dim fileMode As Long
    fileMode = FileAttr(fileNum, 1)
    IsFileOpen = (Err.Number = 0)
End Function

Get All File Handles

Function GetOpenFileHandles() As Collection
    Dim handles As New Collection
    Dim i As Integer
    Dim fileHandle As Long
    For i = 1 To 255
        On Error Resume Next
        fileHandle = FileAttr(i, 2)
        If Err.Number = 0 Then
            handles.Add fileHandle, CStr(i)
        End If
        Err.Clear
    Next i
    Set GetOpenFileHandles = handles
End Function

Validate File Before Operation

Function ValidateFileForReading(fileNum As Integer) As Boolean
    On Error GoTo ErrorHandler
    Dim fileMode As Long
    fileMode = FileAttr(fileNum, 1)
    ' Check if file is open for Input, Random, or Binary
    ValidateFileForReading = (fileMode = 1 Or fileMode = 4 Or fileMode = 32)
    Exit Function
ErrorHandler:
    ValidateFileForReading = False
End Function

Compare File Modes

Sub CompareFileModes(file1 As Integer, file2 As Integer)
    Dim mode1 As Long, mode2 As Long
    On Error Resume Next
    mode1 = FileAttr(file1, 1)
    mode2 = FileAttr(file2, 1)
    If Err.Number = 0 Then
        If mode1 = mode2 Then
            Debug.Print "Files have the same mode: " & GetFileModeDescription(file1)
        Else
            Debug.Print "File1 mode: " & GetFileModeDescription(file1)
            Debug.Print "File2 mode: " & GetFileModeDescription(file2)
        End If
    End If
End Sub

Track File Usage Statistics

Type FileStats
    FileNumber As Integer
    Mode As Long
    Handle As Long
    OpenTime As Date
    OperationCount As Long
End Type
Private fileStatistics() As FileStats
Private statCount As Long
Sub RecordFileOpen(fileNum As Integer)
    On Error Resume Next
    Dim fileMode As Long
    Dim fileHandle As Long
    fileMode = FileAttr(fileNum, 1)
    fileHandle = FileAttr(fileNum, 2)
    If Err.Number = 0 Then
        ReDim Preserve fileStatistics(0 To statCount)
        With fileStatistics(statCount)
            .FileNumber = fileNum
            .Mode = fileMode
            .Handle = fileHandle
            .OpenTime = Now
            .OperationCount = 0
        End With
        statCount = statCount + 1
    End If
End Sub

Platform-Specific File Handle Usage

' Windows API declarations (for demonstration)
Private Declare Function GetFileSize Lib "kernel32" _
    (ByVal hFile As Long, lpFileSizeHigh As Long) As Long
Function GetFileSizeViaHandle(fileNum As Integer) As Long
    Dim fileHandle As Long
    Dim fileSizeHigh As Long
    On Error GoTo ErrorHandler
    ' Get file handle from VB6 file number
    fileHandle = FileAttr(fileNum, 2)
    ' Use Windows API to get file size
    GetFileSizeViaHandle = GetFileSize(fileHandle, fileSizeHigh)
    Exit Function
ErrorHandler:
    GetFileSizeViaHandle = -1
End Function

Advanced Usage

File Access Monitor

Type FileAccessInfo
    FileNumber As Integer
    Mode As String
    Handle As Long
    CanRead As Boolean
    CanWrite As Boolean
    LastChecked As Date
End Type
Function GetFileAccessInfo(fileNum As Integer) As FileAccessInfo
    Dim info As FileAccessInfo
    Dim fileMode As Long
    On Error GoTo ErrorHandler
    fileMode = FileAttr(fileNum, 1)
    With info
        .FileNumber = fileNum
        .Handle = FileAttr(fileNum, 2)
        .LastChecked = Now
        Select Case fileMode
            Case 1  ' Input
                .Mode = "Input"
                .CanRead = True
                .CanWrite = False
            Case 2  ' Output
                .Mode = "Output"
                .CanRead = False
                .CanWrite = True
            Case 4  ' Random
                .Mode = "Random"
                .CanRead = True
                .CanWrite = True
            Case 8  ' Append
                .Mode = "Append"
                .CanRead = False
                .CanWrite = True
            Case 32  ' Binary
                .Mode = "Binary"
                .CanRead = True
                .CanWrite = True
        End Select
    End With
    GetFileAccessInfo = info
    Exit Function
ErrorHandler:
    info.Mode = "Error"
    GetFileAccessInfo = info
End Function

Automatic File Mode Detection for Operations

Function ReadFromFile(fileNum As Integer, ByRef data As Variant) As Boolean
    On Error GoTo ErrorHandler
    Dim fileMode As Long
    fileMode = FileAttr(fileNum, 1)
    ' Read based on detected mode
    Select Case fileMode
        Case 1  ' Input mode
            If Not EOF(fileNum) Then
                Line Input #fileNum, data
                ReadFromFile = True
            End If
        Case 4  ' Random mode
            Get #fileNum, , data
            ReadFromFile = True
        Case 32  ' Binary mode
            Get #fileNum, , data
            ReadFromFile = True
        Case Else
            MsgBox "File not open for reading", vbExclamation
            ReadFromFile = False
    End Select
    Exit Function
ErrorHandler:
    ReadFromFile = False
End Function

File Handle Cache

Private Type HandleCacheEntry
    FileNumber As Integer
    Handle As Long
    CachedTime As Date
End Type
Private handleCache() As HandleCacheEntry
Private cacheSize As Long
Function GetCachedHandle(fileNum As Integer) As Long
    Dim i As Long
    Dim currentTime As Date
    currentTime = Now
    ' Check cache first
    For i = 0 To cacheSize - 1
        If handleCache(i).FileNumber = fileNum Then
            ' Verify cache is still valid (within 1 second)
            If DateDiff("s", handleCache(i).CachedTime, currentTime) < 1 Then
                GetCachedHandle = handleCache(i).Handle
                Exit Function
            End If
        End If
    Next i
    ' Not in cache or expired, get fresh value
    On Error Resume Next
    GetCachedHandle = FileAttr(fileNum, 2)
    If Err.Number = 0 Then
        ' Add to cache
        ReDim Preserve handleCache(0 To cacheSize)
        handleCache(cacheSize).FileNumber = fileNum
        handleCache(cacheSize).Handle = GetCachedHandle
        handleCache(cacheSize).CachedTime = currentTime
        cacheSize = cacheSize + 1
    End If
End Function

Cross-Platform File Handle Wrapper

Function GetPlatformFileInfo(fileNum As Integer) As String
    Dim fileHandle As Long
    Dim info As String
    On Error Resume Next
    fileHandle = FileAttr(fileNum, 2)
    If Err.Number = 0 Then
        info = "File Number: " & fileNum & vbCrLf
        info = info & "Mode: " & GetFileModeDescription(fileNum) & vbCrLf
        info = info & "OS Handle: " & fileHandle & vbCrLf
        ' Platform-specific information
        #If Win32 Then
            info = info & "Platform: Windows 32-bit" & vbCrLf
        #ElseIf Win64 Then
            info = info & "Platform: Windows 64-bit" & vbCrLf
        #Else
            info = info & "Platform: Unknown" & vbCrLf
        #End If
    Else
        info = "File not open"
    End If
    GetPlatformFileInfo = info
End Function

File Descriptor Manager

Private Type FileDescriptor
    VBFileNumber As Integer
    OSHandle As Long
    Mode As Long
    ModeDescription As String
    FilePath As String
    OpenedAt As Date
    IsOpen As Boolean
End Type
Private descriptors As Collection
Sub InitializeDescriptorManager()
    Set descriptors = New Collection
End Sub
Sub RegisterOpenFile(fileNum As Integer, filePath As String)
    Dim desc As FileDescriptor
    On Error Resume Next
    desc.VBFileNumber = fileNum
    desc.OSHandle = FileAttr(fileNum, 2)
    desc.Mode = FileAttr(fileNum, 1)
    desc.ModeDescription = GetFileModeDescription(fileNum)
    desc.FilePath = filePath
    desc.OpenedAt = Now
    desc.IsOpen = (Err.Number = 0)
    If desc.IsOpen Then
        descriptors.Add desc, "FD" & fileNum
    End If
End Sub
Function GetDescriptor(fileNum As Integer) As FileDescriptor
    On Error Resume Next
    GetDescriptor = descriptors("FD" & fileNum)
End Function

Comprehensive File State Checker

Function GetCompleteFileState(fileNum As Integer) As String
    Dim state As String
    Dim fileMode As Long
    Dim fileHandle As Long
    On Error Resume Next
    state = "=== File State for #" & fileNum & " ===" & vbCrLf
    fileMode = FileAttr(fileNum, 1)
    If Err.Number <> 0 Then
        state = state & "File is CLOSED or invalid file number" & vbCrLf
        GetCompleteFileState = state
        Exit Function
    End If
    state = state & "File is OPEN" & vbCrLf
    state = state & "Mode: " & GetFileModeDescription(fileNum) & " (" & fileMode & ")" & vbCrLf
    fileHandle = FileAttr(fileNum, 2)
    state = state & "OS Handle: " & fileHandle & vbCrLf
    ' Add capabilities
    state = state & "Capabilities:" & vbCrLf
    Select Case fileMode
        Case 1
            state = state & "  - Read: Yes" & vbCrLf
            state = state & "  - Write: No" & vbCrLf
            state = state & "  - EOF applicable: Yes" & vbCrLf
        Case 2
            state = state & "  - Read: No" & vbCrLf
            state = state & "  - Write: Yes" & vbCrLf
            state = state & "  - EOF applicable: No" & vbCrLf
        Case 4
            state = state & "  - Read: Yes" & vbCrLf
            state = state & "  - Write: Yes" & vbCrLf
            state = state & "  - EOF applicable: Yes" & vbCrLf
        Case 8
            state = state & "  - Read: No" & vbCrLf
            state = state & "  - Write: Yes (append only)" & vbCrLf
            state = state & "  - EOF applicable: No" & vbCrLf
        Case 32
            state = state & "  - Read: Yes" & vbCrLf
            state = state & "  - Write: Yes" & vbCrLf
            state = state & "  - EOF applicable: Use LOF/Seek" & vbCrLf
    End Select
    GetCompleteFileState = state
End Function

Error Handling

Function SafeFileAttr(fileNum As Integer, returnType As Long) As Variant
    On Error GoTo ErrorHandler
    ' Validate returnType
    If returnType <> 1 And returnType <> 2 Then
        Err.Raise 5, , "Invalid returnType. Must be 1 or 2."
    End If
    SafeFileAttr = FileAttr(fileNum, returnType)
    Exit Function
ErrorHandler:
    Select Case Err.Number
        Case 52  ' Bad file name or number
            MsgBox "File #" & fileNum & " is not open", vbExclamation
            SafeFileAttr = Null
        Case 5   ' Invalid procedure call
            MsgBox "Invalid returnType parameter", vbExclamation
            SafeFileAttr = Null
        Case Else
            MsgBox "Error " & Err.Number & ": " & Err.Description, vbCritical
            SafeFileAttr = Null
    End Select
End Function

Common Errors

Error 52 (Bad file name or number): File number is invalid or file is closed
Error 5 (Invalid procedure call): returntype is not 1 or 2

Performance Considerations

FileAttr is very fast (simple state query)
Minimal overhead for checking file state
More efficient than maintaining separate state variables
File handle retrieval (returntype=2) is as fast as mode retrieval
Consider caching results if calling frequently in tight loops

Best Practices

Always Validate File Is Open

' Good - Check before operations
On Error Resume Next
fileMode = FileAttr(fileNum, 1)
If Err.Number <> 0 Then
    MsgBox "File is not open"
    Exit Sub
End If
On Error GoTo 0
' Or use IsFileOpen helper
If Not IsFileOpen(fileNum) Then
    Exit Sub
End If

Use Constants for Return Types

' Good - Define constants for clarity
Const FILE_ATTR_MODE = 1
Const FILE_ATTR_HANDLE = 2
fileMode = FileAttr(fileNum, FILE_ATTR_MODE)
fileHandle = FileAttr(fileNum, FILE_ATTR_HANDLE)

Comparison with Other Functions

`FileAttr` vs `GetAttr`

' FileAttr - For open files, returns mode or handle
fileMode = FileAttr(fileNum, 1)  ' File must be open
' GetAttr - For any file, returns attributes (readonly, hidden, etc.)
attrs = GetAttr("C:\file.txt")   ' File can be closed

`FileAttr` vs `LOF`

' FileAttr - Returns mode or handle
fileMode = FileAttr(fileNum, 1)
' LOF - Returns file length in bytes
fileSize = LOF(fileNum)

Limitations

Only works with files opened via VB6 Open statement
Cannot get attributes of closed files
returntype must be exactly 1 or 2
File handle is platform-specific
No information about file path or name
Cannot determine if file is at EOF
Does not indicate file position

FreeFile: Returns next available file number
Open: Opens a file for reading or writing
Close: Closes an open file
LOF: Returns length of open file
Seek: Returns or sets current position in file
EOF: Returns whether end of file reached
GetAttr: Returns attributes of any file (readonly, hidden, etc.)