`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.)

FileAttr Function