Seek Function

Returns a Long specifying the current read/write position within a file opened using Open statement.

Syntax

Seek(filenumber)

Parameters

filenumber - Required. Any valid Integer file number.

Return Value

Returns a Long value indicating the current position in the file: - For Random mode files: Returns the record number of the next record to be read or written (1-based) - For Binary, Output, Append, and Input mode files: Returns the byte position where the next operation occurs (1-based) - Position 1 is the beginning of the file

Remarks

The Seek function is used to determine the current position in a file opened with the Open statement. It is particularly useful for: - Determining current position before reading/writing - Saving position to return to later - Calculating file progress (current position vs file size using LOF) - Implementing custom file navigation - Verifying position after Seek statement For Random access files, Seek returns the record number (1-based) of the next record to be read or written. For all other access modes (Binary, Input, Output, Append), Seek returns the byte position (1-based). The Seek function is different from the Seek statement: - Seek function: Returns current position (read-only operation) - Seek statement: Sets the position for next read/write (write operation) The file must be open before calling Seek. Use FreeFile to get an available file number. Always close files when done using Close statement.

Typical Uses

Current Position: Determine where you are in the file
Save Position: Store current position to return to later
Progress Tracking: Calculate percentage of file processed
Navigation: Implement forward/backward navigation in files
Record Counting: Count records processed in Random access
Byte Counting: Track bytes read/written in Binary mode
Position Verification: Verify Seek statement worked correctly
File Parsing: Parse structured binary files with position tracking

Basic Examples

' Example 1: Get current position in binary file
Dim FileNum As Integer
Dim CurrentPos As Long
FileNum = FreeFile
Open "data.bin" For Binary As #FileNum
CurrentPos = Seek(FileNum)  ' Returns 1 at start
Debug.Print "Position: " & CurrentPos
Close #FileNum

' Example 2: Get current record number in random access
Dim FileNum As Integer
Dim RecordNum As Long
FileNum = FreeFile
Open "records.dat" For Random As #FileNum Len = 100
RecordNum = Seek(FileNum)  ' Returns next record number
Debug.Print "Next Record: " & RecordNum
Close #FileNum

' Example 3: Save and restore position
Dim FileNum As Integer
Dim SavedPos As Long
FileNum = FreeFile
Open "data.txt" For Input As #FileNum
' Read some data...
SavedPos = Seek(FileNum)  ' Save position
' Read more data...
Seek #FileNum, SavedPos   ' Restore position
Close #FileNum

' Example 4: Calculate progress percentage
Dim FileNum As Integer
Dim Progress As Double
FileNum = FreeFile
Open "large.dat" For Binary As #FileNum
Progress = (Seek(FileNum) / LOF(FileNum)) * 100
Debug.Print "Progress: " & Format(Progress, "0.0") & "%"
Close #FileNum

Common Patterns

Pattern 1: `GetCurrentPosition`

Get current file position with error handling

Function GetCurrentPosition(FileNum As Integer) As Long
    On Error Resume Next
    GetCurrentPosition = Seek(FileNum)
    If Err.Number <> 0 Then
        GetCurrentPosition = -1  ' Error indicator
    End If
End Function

Pattern 2: `GetProgressPercentage`

Calculate how much of file has been processed

Function GetProgressPercentage(FileNum As Integer) As Double
    Dim CurrentPos As Long
    Dim FileSize As Long
    CurrentPos = Seek(FileNum)
    FileSize = LOF(FileNum)
    If FileSize > 0 Then
        GetProgressPercentage = (CurrentPos / FileSize) * 100
    Else
        GetProgressPercentage = 0
    End If
End Function

Pattern 3: `IsAtEndOfFile`

Check if at end of file using position

Function IsAtEndOfFile(FileNum As Integer) As Boolean
    IsAtEndOfFile = (Seek(FileNum) > LOF(FileNum))
End Function

Pattern 4: `GetRemainingBytes`

Calculate bytes remaining in file

Function GetRemainingBytes(FileNum As Integer) As Long
    GetRemainingBytes = LOF(FileNum) - Seek(FileNum) + 1
End Function

Pattern 5: `SaveAndRestorePosition`

Save position, perform operation, restore

Sub SaveAndRestorePosition(FileNum As Integer)
    Dim SavedPos As Long
    SavedPos = Seek(FileNum)
    ' Perform operations that change position
    Seek #FileNum, 1  ' Go to start
    ' Read header...
    Seek #FileNum, SavedPos  ' Restore position
End Sub

Pattern 6: `GetCurrentRecordNumber`

Get current record in Random access file

Function GetCurrentRecordNumber(FileNum As Integer) As Long
    ' For Random access, Seek returns record number
    GetCurrentRecordNumber = Seek(FileNum)
End Function

Pattern 7: `CalculateBytesProcessed`

Track bytes processed since start

Function CalculateBytesProcessed(FileNum As Integer, StartPos As Long) As Long
    CalculateBytesProcessed = Seek(FileNum) - StartPos
End Function

Pattern 8: `ValidateFilePosition`

Verify position is within file bounds

Function ValidateFilePosition(FileNum As Integer) As Boolean
    Dim CurrentPos As Long
    Dim FileSize As Long
    CurrentPos = Seek(FileNum)
    FileSize = LOF(FileNum)
    ValidateFilePosition = (CurrentPos >= 1 And CurrentPos <= FileSize + 1)
End Function

Pattern 9: `GetPositionInfo`

Get detailed position information

Sub GetPositionInfo(FileNum As Integer, ByRef Position As Long, _
                    ByRef Size As Long, ByRef Remaining As Long)
    Position = Seek(FileNum)
    Size = LOF(FileNum)
    Remaining = Size - Position + 1
End Sub

Pattern 10: `SeekToPercentage`

Jump to percentage of file

Sub SeekToPercentage(FileNum As Integer, Percentage As Double)
    Dim TargetPos As Long
    TargetPos = CLng((LOF(FileNum) * Percentage) / 100)
    If TargetPos < 1 Then TargetPos = 1
    Seek #FileNum, TargetPos
    Debug.Print "Moved to position: " & Seek(FileNum)
End Sub

Advanced Usage

Example 1: `FilePositionTracker` Class

Track and manage file positions with bookmarks

' Class: FilePositionTracker
Private m_FileNum As Integer
Private m_Bookmarks As Collection
Private Sub Class_Initialize()
    Set m_Bookmarks = New Collection
End Sub
Public Sub Initialize(FileNum As Integer)
    m_FileNum = FileNum
End Sub
Public Function GetCurrentPosition() As Long
    GetCurrentPosition = Seek(m_FileNum)
End Function
Public Sub AddBookmark(BookmarkName As String)
    Dim CurrentPos As Long
    CurrentPos = Seek(m_FileNum)
    On Error Resume Next
    m_Bookmarks.Remove BookmarkName
    On Error GoTo 0
    m_Bookmarks.Add CurrentPos, BookmarkName
End Sub
Public Sub GoToBookmark(BookmarkName As String)
    Dim BookmarkPos As Long
    On Error Resume Next
    BookmarkPos = m_Bookmarks(BookmarkName)
    If Err.Number = 0 Then
        Seek #m_FileNum, BookmarkPos
    Else
        Err.Raise vbObjectError + 1001, "FilePositionTracker", _
                  "Bookmark not found: " & BookmarkName
    End If
End Sub
Public Function GetProgress() As Double
    Dim CurrentPos As Long
    Dim FileSize As Long
    CurrentPos = Seek(m_FileNum)
    FileSize = LOF(m_FileNum)
    If FileSize > 0 Then
        GetProgress = (CDbl(CurrentPos) / CDbl(FileSize)) * 100
    Else
        GetProgress = 0
    End If
End Function
Public Function GetRemainingBytes() As Long
    GetRemainingBytes = LOF(m_FileNum) - Seek(m_FileNum) + 1
End Function
Public Sub ClearBookmarks()
    Set m_Bookmarks = New Collection
End Sub

Example 2: `BinaryFileParser` Module

Parse structured binary files with position tracking

' Module: BinaryFileParser
Private Type FileHeader
    Signature As String * 4
    Version As Integer
    RecordCount As Long
End Type
Public Function ParseFile(FileName As String) As Collection
    Dim FileNum As Integer
    Dim Header As FileHeader
    Dim Records As New Collection
    Dim i As Long
    Dim StartPos As Long
    FileNum = FreeFile
    Open FileName For Binary As #FileNum
    ' Read header
    StartPos = Seek(FileNum)
    Debug.Print "Reading header at position: " & StartPos
    Get #FileNum, , Header
    Debug.Print "Header read, now at position: " & Seek(FileNum)
    ' Validate signature
    If Header.Signature <> "DATA" Then
        Close #FileNum
        Err.Raise vbObjectError + 1001, "ParseFile", "Invalid file signature"
    End If
    ' Read records
    For i = 1 To Header.RecordCount
        Dim RecordPos As Long
        Dim RecordData As String
        RecordPos = Seek(FileNum)
        Debug.Print "Reading record " & i & " at position: " & RecordPos
        ' Read record (example: 100 byte records)
        RecordData = Space$(100)
        Get #FileNum, , RecordData
        Records.Add RecordData
    Next i
    Debug.Print "Finished at position: " & Seek(FileNum)
    Debug.Print "File size: " & LOF(FileNum)
    Close #FileNum
    Set ParseFile = Records
End Function
Public Function GetFileProgress(FileNum As Integer) As String
    Dim CurrentPos As Long
    Dim FileSize As Long
    Dim Percentage As Double
    CurrentPos = Seek(FileNum)
    FileSize = LOF(FileNum)
    If FileSize > 0 Then
        Percentage = (CDbl(CurrentPos) / CDbl(FileSize)) * 100
    Else
        Percentage = 0
    End If
    GetFileProgress = "Position: " & CurrentPos & " of " & FileSize & _
                      " (" & Format(Percentage, "0.0") & "%)"
End Function

Example 3: `RandomAccessNavigator` Class

Navigate through Random access file records

' Class: RandomAccessNavigator
Private m_FileNum As Integer
Private m_RecordLength As Integer
Private m_TotalRecords As Long
Public Sub Initialize(FileName As String, RecordLength As Integer)
    m_RecordLength = RecordLength
    m_FileNum = FreeFile
    Open FileName For Random As #m_FileNum Len = RecordLength
    m_TotalRecords = LOF(m_FileNum) \ RecordLength
End Sub
Public Function GetCurrentRecord() As Long
    ' For Random access, Seek returns record number
    GetCurrentRecord = Seek(m_FileNum)
End Function
Public Function GetTotalRecords() As Long
    GetTotalRecords = m_TotalRecords
End Function
Public Function MoveNext() As Boolean
    Dim CurrentRecord As Long
    CurrentRecord = Seek(m_FileNum)
    If CurrentRecord <= m_TotalRecords Then
        ' Seek statement will auto-advance after Get
        MoveNext = True
    Else
        MoveNext = False
    End If
End Function
Public Sub MovePrevious()
    Dim CurrentRecord As Long
    CurrentRecord = Seek(m_FileNum)
    If CurrentRecord > 1 Then
        Seek #m_FileNum, CurrentRecord - 1
    End If
End Sub
Public Sub MoveFirst()
    Seek #m_FileNum, 1
End Sub
Public Sub MoveLast()
    Seek #m_FileNum, m_TotalRecords
End Sub
Public Function IsAtBeginning() As Boolean
    IsAtBeginning = (Seek(m_FileNum) = 1)
End Function
Public Function IsAtEnd() As Boolean
    IsAtEnd = (Seek(m_FileNum) > m_TotalRecords)
End Function
Public Function GetProgress() As Double
    Dim CurrentRecord As Long
    CurrentRecord = Seek(m_FileNum)
    If m_TotalRecords > 0 Then
        GetProgress = (CDbl(CurrentRecord - 1) / CDbl(m_TotalRecords)) * 100
    Else
        GetProgress = 0
    End If
End Function
Public Sub Close()
    Close #m_FileNum
End Sub

Example 4: `FileProgressMonitor` Class

Monitor file processing progress with time estimates

' Class: FileProgressMonitor
Private m_FileNum As Integer
Private m_StartPosition As Long
Private m_StartTime As Double
Private m_FileSize As Long
Public Sub StartMonitoring(FileNum As Integer)
    m_FileNum = FileNum
    m_StartPosition = Seek(FileNum)
    m_StartTime = Timer
    m_FileSize = LOF(FileNum)
End Sub
Public Function GetCurrentPosition() As Long
    GetCurrentPosition = Seek(m_FileNum)
End Function
Public Function GetBytesProcessed() As Long
    GetBytesProcessed = Seek(m_FileNum) - m_StartPosition
End Function
Public Function GetPercentComplete() As Double
    Dim CurrentPos As Long
    CurrentPos = Seek(m_FileNum)
    If m_FileSize > 0 Then
        GetPercentComplete = (CDbl(CurrentPos) / CDbl(m_FileSize)) * 100
    Else
        GetPercentComplete = 0
    End If
End Function
Public Function GetElapsedSeconds() As Double
    GetElapsedSeconds = Timer - m_StartTime
End Function
Public Function GetEstimatedTimeRemaining() As Double
    Dim BytesProcessed As Long
    Dim BytesRemaining As Long
    Dim ElapsedTime As Double
    Dim BytesPerSecond As Double
    BytesProcessed = Seek(m_FileNum) - m_StartPosition
    BytesRemaining = m_FileSize - Seek(m_FileNum) + 1
    ElapsedTime = Timer - m_StartTime
    If BytesProcessed > 0 And ElapsedTime > 0 Then
        BytesPerSecond = BytesProcessed / ElapsedTime
        GetEstimatedTimeRemaining = BytesRemaining / BytesPerSecond
    Else
        GetEstimatedTimeRemaining = 0
    End If
End Function
Public Function GetProgressReport() As String
    Dim Report As String
    Dim PercentComplete As Double
    Dim ElapsedTime As Double
    Dim RemainingTime As Double
    PercentComplete = GetPercentComplete()
    ElapsedTime = GetElapsedSeconds()
    RemainingTime = GetEstimatedTimeRemaining()
    Report = "Progress: " & Format(PercentComplete, "0.0") & "%" & vbCrLf
    Report = Report & "Position: " & Seek(m_FileNum) & " of " & m_FileSize & vbCrLf
    Report = Report & "Elapsed: " & Format(ElapsedTime, "0.0") & "s" & vbCrLf
    Report = Report & "Remaining: " & Format(RemainingTime, "0.0") & "s"
    GetProgressReport = Report
End Function
Public Sub Reset()
    m_StartPosition = Seek(m_FileNum)
    m_StartTime = Timer
End Sub

Error Handling

The Seek function can generate the following errors: - Error 52 (Bad file name or number): File not open or invalid file number - Error 5 (Invalid procedure call): File number is invalid Always use error handling when working with file I/O:

On Error Resume Next
CurrentPos = Seek(FileNum)
If Err.Number <> 0 Then
    MsgBox "Error getting position: " & Err.Description
End If

Performance Considerations

Seek function is very fast (just reads internal file pointer)
No disk I/O involved (unlike reading/writing data)
Can be called frequently without performance impact
Useful for progress tracking in loops without overhead
Combine with LOF for efficient progress calculations

Best Practices

Validate File Number: Ensure file is open before calling Seek
Use with LOF: Combine with LOF function to calculate progress
Error Handling: Always use error handling for file operations
Close Files: Always close files when done to free resources
Save Position: Store position before operations that change it
1-Based Position: Remember positions start at 1, not 0
Mode Awareness: Know whether function returns record# or byte position
FreeFile Usage: Use FreeFile to get available file numbers
Progress Updates: Update UI periodically, not on every byte
Position Validation: Verify position is within expected range

Function/Statement	Purpose	Returns	Mode-Specific
Seek (Function)	Get current position	Long (position)	Record# or byte position
Seek (Statement)	Set position	N/A (void)	Sets for next operation
LOF	Get file size	Long (bytes)	Total file size
EOF	Check end of file	Boolean	True if past end
Loc	Get current position	Long	Similar to Seek
`FileLen`	Get file length	Long (bytes)	File must be closed

Platform Considerations

Available in VB6, VBA (all versions)
1-based positioning (unlike many other languages)
Maximum file size limited by Long data type (2GB)
For files > 2GB, position may overflow
Random access mode returns record numbers
All other modes return byte positions

Limitations

Cannot handle files larger than 2GB (Long overflow)
File must be open before calling Seek
Returns position for next operation (not last operation)
For Random access, assumes fixed-length records
No support for 64-bit file positions
Cannot determine position in closed files

Seek (Statement): Set the position for next read/write operation
LOF: Get the length of an open file in bytes
EOF: Determine if end of file has been reached
Loc: Get the current read/write position (similar to Seek function)
Get: Read data from file (advances position)
Put: Write data to file (advances position)
Open: Open file for I/O operations
Close: Close an open file
FreeFile: Get next available file number

Seek Function

Syntax

Parameters

Return Value

Remarks

Typical Uses

Basic Examples

Common Patterns

Pattern 1: GetCurrentPosition

Pattern 2: GetProgressPercentage

Pattern 3: IsAtEndOfFile

Pattern 4: GetRemainingBytes

Pattern 5: SaveAndRestorePosition

Pattern 6: GetCurrentRecordNumber

Pattern 7: CalculateBytesProcessed

Pattern 8: ValidateFilePosition

Pattern 9: GetPositionInfo

Pattern 10: SeekToPercentage