Seek
Returns or sets the read/write position within a file opened by using the Open statement.
Seek Function
Returns a Long specifying the current read/write position within an open file.
Syntax: Seek( filenumber )
- filenumber
- required Integer containing a valid file number.
Seek returns a value between 1 and 2,147,483,647 (2^31 − 1), inclusive.
| Mode | Return value |
|---|---|
| Random | Number of the next record to be read or written. |
| Binary, Output, Append, Input | Byte position at which the next operation takes place. The first byte in a file is at position 1. |
Seek Statement
Sets the position for the next read/write operation within an open file.
Syntax: Seek [ # ] filenumber, position
- filenumber
- required Any valid file number.
- position
- required Number in the range 1–2,147,483,647 indicating where the next read/write operation should occur.
Record numbers specified in Get and Put statements override file positioning performed by Seek.
Performing a file-write operation after a Seek operation beyond the end of a file extends the file. Attempting a Seek to a negative or zero position causes an error.
Examples
This example assumes that TESTFILE contains records of the user-defined type Record.
Type Record ' Define user-defined type.
ID As Integer
Name As String * 20
End Type
For files opened in Random mode, the Seek function returns the number of the next record.
Dim MyRecord As Record
Open "TESTFILE" For Random As #1 Len = Len(MyRecord)
Do While Not EOF(1) ' Loop until end of file.
Get #1, , MyRecord ' Read next record.
Debug.Print Seek(1) ' Print record number.
Loop
Close #1 ' Close file.
The Seek statement can set the record position. This example reads records in reverse order.
Dim MyRecord As Record, MaxSize, RecordNumber
Open "TESTFILE" For Random As #1 Len = Len(MyRecord)
MaxSize = LOF(1) \ Len(MyRecord) ' Get number of records in file.
For RecordNumber = MaxSize To 1 Step -1
Seek #1, RecordNumber ' Set position.
Get #1, , MyRecord ' Read record.
Next RecordNumber
Close #1 ' Close file.
For files opened in modes other than Random, Seek returns or sets the byte position.
Dim MyChar
Open "TESTFILE" For Input As #1 ' Open file for reading.
Do While Not EOF(1) ' Loop until end of file.
MyChar = Input(1, #1) ' Read next character.
Debug.Print Seek(1) ' Print byte position.
Loop
Close #1 ' Close file.