Action

Function: Returns the position of the next Byte to be read or written

Statement: Sets the position of the next Byte to be read or written

Syntax

Function: NextReadWrite = Seek (#bFileNumber)

Statement: Seek #bFileNumber, NewPos

Remarks

This function returns the position of the next Byte to be read or written. If an error occures, 0 is returned. Check DOS-Error in variable gbDOSError.

The statetement also returns an error in the gbDOSerror variable in the event that an error occurs.
You can for example not set the fileposition behinds the filesize.

In QB/VB the file is filled with 0 bytes when you set the filepointer behind the size of the file. For embedded systems this does not seem a good idea.

Seek and Loc seems to do the same function, but take care : the seek function will return the position of the next read/write, while the Loc function returns the position of the last read/write. You may say that Seek = Loc+1.

Difference with QB

In QB/VB you can use seek to make the file bigger. When a file is 100 bytes long, setting the filepointer to 200 will increase the file with 0 bytes. By design this is not the case in AVR-DOS.

ASM

Example

Open "test.biN" For Binary As #2
Put #2 , B ' write a byte
Put #2 , W ' write a word
Put #2 , L ' write a long
Ltemp = Loc(#2) + 1 ' get the position of the next byte
Print Ltemp ; " LOC" ' store the location of the file pointer
Print Seek(#2) ; " = LOC+1"

Close #2

'now open the file again and write only the single
Open "test.bin" For Binary As #2
Seek #2 , Ltemp ' set the filepointer
Sn = 1.23 ' change the single value so we can check it better
Put #2 , Sn = 1 'specify the file position
Close #2