SEEK
Contents |
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
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bFileNumber |
(Byte) Filenumber, which identifies an opened file |
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NextReadWrite |
A Long Variable, which is assigned with the Position of the next Byte to be read or written (1-based) |
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NewPos |
A Long variable that holds the new position the file pointer must be set too. |
This function returns the position of the next Byte to be read or written. If an error occurs, 0 is returned. Check DOS-Error in variable gbDOSError.
The statement also returns an error in the gbDOSerror variable in the event that an error occurs.
You can for example not set the file position behinds the file size.
In VB the file is filled with 0 bytes when you set the file pointer 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.
See also
INITFILESYSTEM , OPEN , CLOSE, FLUSH , PRINT, LINE INPUT, LOC, LOF , EOF , FREEFILE , FILEATTR , BSAVE , BLOAD ,KILL , DISKFREE , DISKSIZE , GET , PUT , FILEDATE , FILETIME , FILEDATETIME , DIR , FILELEN , WRITE , INPUT
ASM
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Function Calls |
_FileSeek |
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Input |
r24: filenumber |
X: Pointer to Long-variable, which gets the result |
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Output |
r25: Errorcode |
C-Flag: Set on Error |
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Statement Calls |
_FileSeekSet |
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Input |
r24: filenumber |
X: Pointer to Long-variable with the position |
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Output |
r25: Errorcode |
C-Flag: Set on Error |
Partial 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
Partial Example 2
'------------------------------------------------------------------------------ ' simulate-AVR-DOS.bas ' simulate AVR-DOS using virtual XRAM drive ' '------------------------------------------------------------------------------ $regfile = "M128def.dat" $crystal = 16000000 ' Adjust HW Stack, Soft-Stack and Frame size to 128 minimum each!!! $hwstack = 128 : $swstack = 128 : $framesize = 128 $xramsize = &H10000 'specify 64KB of XRAM for the file system $sim 'for simulation only ! $baud = 19200 Config Clock = Soft Enable Interrupts Config Date = Mdy , Separator = Dot Dim Btemp1 As Byte , Battr1 As Byte , Battr2 As Byte $include "Config_XRAMDrive.bas" ' Does drive init too $include "Config_AVR-DOS.BAS" Print "Wait for Drive" If Gbdriveerror = 0 Then Print "Init File System ... "; Btemp1 = Initfilesystem(1) ' Partition 1 ' use 0 for drive without Master boot record If Btemp1 <> 0 Then Print "Error: " ; Btemp1 ; " at Init file system" Else Print " OK" Print "Filesystem: " ; Gbfilesystem Print "FAT Start Sector: " ; Glfatfirstsector Print "Root Start Sector: " ; Glrootfirstsector Print "Data First Sector: " ; Gldatafirstsector Print "Max. Cluster Nummber: " ; Glmaxclusternumber Print "Sectors per Cluster: " ; Gbsectorspercluster Print "Root Entries: " ; Gwrootentries Print "Sectors per FAT: " ; Glsectorsperfat Print "Number of FATs: " ; Gbnumberoffats End If Else Print "Error during Drive Init: " ; Gbdriveerror End If Dim Lpos As Long Open "test.bin" For Binary As #11 Print Seek(#11) ' 1 Put #11 , Btemp1 Print Seek(#11) ' 2 Lpos = Lof(#11) + 1 ' 1+1=2 Seek #11 , Lpos Put #11 , Btemp1 Print Seek(#11) '3 Close #11 End
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