Seek Statement

Sets the position for the next read or write operation in a file opened using the Open statement.

Syntax

Seek [#]filenumber, position

Parts

• filenumber: Required. Any valid file number. The number sign (#) is optional but commonly included for clarity.
• position: Required. Number in the range 1 to 2,147,483,647 (equivalent to 2^31 - 1), indicating where the next read or write should occur.

Remarks

• File Position: The Seek statement sets the byte position in a file where the next Input, Output, Get, or Put operation will occur.
• Position Numbering: File positions are numbered beginning with 1 (the first byte in the file is at position 1, not 0).
• Random Access Files: For Random mode files, the position parameter specifies a record number rather than a byte position.
• Sequential Files: For files opened in Input, Output, or Append mode, position specifies the byte position.
• Binary Files: For Binary mode files, position specifies the byte position.
• Seek Function: Use the Seek function (without arguments except file number) to return the current file position.
• EOF Behavior: Setting the position beyond the end of the file doesn't immediately extend the file, but writing to that position will.
• Position Range: The position must be a positive Long value (1 to 2,147,483,647).
• File Number: The file must be opened before using Seek.

Position Interpretation by File Mode

Examples

Seek to Beginning of File

Open "DATA.TXT" For Binary As #1
Seek #1, 1   ' Position at first byte
' Read or write operations
Close #1

Seek to Specific Byte Position

Open "BINARY.DAT" For Binary As #1
Seek #1, 100   ' Position at byte 100
Get #1, , myData
Close #1

Seek to Specific Record in Random File

Type Employee
ID As Integer
Name As String * 30
End Type

Dim emp As Employee
Open "EMPLOYEE.DAT" For Random As #1 Len = Len(emp)
Seek #1, 5   ' Position at record 5
Get #1, , emp
Close #1

Seek Based on Calculation

Dim recordNumber As Long
recordNumber = 10
Seek #1, recordNumber

Using Seek with Loop

Open "DATA.BIN" For Binary As #1
For i = 1 To 100 Step 10
Seek #1, i
Put #1, , dataArray(i)
Next i
Close #1

Seek to End of File

Open "APPEND.TXT" For Binary As #1
Seek #1, LOF(1) + 1   ' Position after last byte
Put #1, , newData
Close #1

Combined with Seek Function

Open "DATA.TXT" For Binary As #1
currentPos = Seek(1)      ' Get current position
Seek #1, currentPos + 50  ' Move 50 bytes forward
Close #1

Rewind File

Sub RewindFile(fileNum As Integer)
Seek fileNum, 1  ' Return to beginning
End Sub

Seek in Random Access Processing

Type Product
Code As String * 10
Price As Double
End Type

Dim prod As Product
Dim recordNum As Long

Open "PRODUCTS.DAT" For Random As #1 Len = Len(prod)
recordNum = 25
Seek #1, recordNum
Get #1, , prod
prod.Price = prod.Price * 1.1  ' Increase price by 10%
Seek #1, recordNum
Put #1, , prod
Close #1

Common Errors

• Error 52: Bad file name or number - file not open or invalid file number
• Error 63: Bad record number - position is less than 1 or exceeds valid range
• Error 5: Invalid procedure call - negative or zero position value

Performance Tips

• For sequential reading/writing, you generally don't need Seek as the file pointer advances automatically.
• Use Seek when you need random access to specific parts of a file.
• Combining Seek with the Seek function allows you to save and restore file positions.
• For large files, seeking to specific positions is much faster than reading sequentially.

See Also

• Seek function (returns current file position)
• Get statement (read data from file)
• Put statement (write data to file)
• Open statement (open files)
• LOF function (length of file)
• Loc function (current position in file)

References

• Seek Statement - Microsoft Docs