PBSetFPosSync

PBSetFPos Set position of an open file's file mark

#include <Files.h> File Manager (PBxxx)

OSErr PBSetFPos(pb, async );

ParmBlkPtr pb ; address of a 50-byte IOParam structure

Boolean async ; 0=await completion; 1=immediate return

returns Error Code; 0=no error

PBSetFPos selects a new position for the file mark (the place where the

next read or write will start) of an open file.

pb is the address of a 50-byte IOParam structure. The relevant fields

are:

Out-In Name Type Size Offset Description

-> ioCompletion ProcPtr 4 12 Completion routine address (if async =TRUE)

-> ioRefNum short 2 24 File reference number

-> ioPosMode short 2 44 Positioning Mode (1=absolute, 2=from EOF, et.al)

<-> ioPosOffset long 4 46 Entry: Position delta (bytes from start,EOF,...)

Return: New value of mark (from start of file)

<- ioResult OSErr 2 16 Error Code (0=no error, 1=not done yet)

async is a Boolean value. Use FALSE for normal (synchronous) operation

or TRUE to enqueue the request and resume control immediately. See

Async I/O.

Returns: an operating system Error Code. It will be one of:

noErr (0) No error

eofErr (-39) End of file

extFSErr (-58) External file system

fnOpnErr (-38) File not open

ioErr (-36) I/O error

posErr (-40) Can't position to before start of file

rfNumErr (-51) Bad ioRefNum

Notes: Since you can set ioPosOffset when you call PBRead and PBWrite,

PBSetFPos is not needed often.

In random-access database operations, watch for the eofErr return value.

You may need to enlarge the file via PBSetEOF or PBAllocate.