PBSetEOFSync
PBSetEOF Set the logical file size of an open file
#include <Files.h> File Manager (PBxxx)
OSErr PBSetEOF(pb, async ); Boolean async ; 0=await completion; 1=immediate return PBSetEOF lets you expand or truncate the logical size of an open file. The
file must be open with read/write permission.
pb is the address of a 50-byte IOParam structure. The relevant fields are as follows:
Out-In Name Type Size Offset Description
-> ioCompletion ProcPtr 4 12 Completion routine address (if async =TRUE) -> ioRefNum short 2 24 File reference number
-> ioMisc Ptr 4 28 Desired logical file size, in bytes <- 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.
noErr (0) No error
dskFulErr (-34) Disk full
extFSErr (-58) External file system
fLckdErr (-45) File is locked
fnOpnErr (-38) File not open
ioErr (-36) I/O error
rfNumErr (-51) Bad ioRefNum
vLckdErr (-46) Volume is locked
wPrErr (-44) Diskette is write-protected
wrPermErr (-61) Write permissions error
Notes: Place the desired size in ioMisc. Since that structure field is declared as a
type Ptr, you will need to coerce the desired size from a long integer to a
Ptr:
long newSize;
newSize = 1000L;
pb.ioRefNum = myFileRef;
pb.ioMisc = (Ptr)newSize;
err = PBSetEOF( &pb, FALSE ); If you set the logical EOF to a value larger than its physical EOF, additional
disk blocks will be allocated to the file. If there is not enough space on the
disk to satisfy the request, no change is made and the function returns
Using a smaller size will truncate the file. The resulting physical EOF will
be the value of ioMisc, rounded up to the next higher block size. Use
ioMisc=0 to truncate all data from the open fork of the file and release all
of its storage on the volume.
You can use PBAllocate or PBAllocContig to increase the physical size
of the file, without affecting the logical EOF. Use PBGetFInfo to obtain the current value of the physical EOF.
Note that since sequential write operations (starting at the end of the file)
increase the EOF automatically, this function is rarely needed.