FS_CHGFILEPTR

Move a file's logical read/write position pointer.

Syntax

FS_CHGFILEPTR(psffsi, psffsd, offset, type, IOflag)

Parameters

psffsi: Is a pointer to the file-system-independent portion of an open file instance.

The FSD uses the current file size or sfi_position along with offset and type to compute a new sfi_position. This is updated by the system.

psffsd: Is a pointer to the file-system-dependent portion of an open file instance. The FSD may store or adjust data as appropriate in this structure.

offset: Is the signed offset to be added to the current file size or position to form the new position within the file.

type: Indicates the basis of a seek operation.

type == 0 indicates seek relative to beginning of file.

type == 1 indicates seek relative to current position within the file.

type == 2 indicates seek relative to end of file.

The value of type passed to the FSD will be valid.

IOflag: Indicates information about the operation on the handle.; IOflag == 0x0010 indicates write-through.; IOflag == 0x0020 indicates no-cache.

Returns

Sample

Calling Sequence

int far pascal FS_CHGFILEPTR(psffsi, psffsd, offset, type, IOflag)

struct sffsi far * psffsi;
struct sffsd far * psffsd;
long offset;
unsigned short type;
unsigned short IOflag;

Remarks

The file system may want to take the seek operation as a hint that an I/O operation is about to take place at the new position and initiate a positioning operation on sequential access media or read-ahead operation on other media.

Some DOS mode programs expect to be able to do a negative seek. OS/2 passes these requests on to the FSD and returns an error for OS/2 mode negative seek requests. Because a seek to a negative position is, effectively, a seek to a very large offset, it is suggested that the FSD return end-of-file for subsequent read requests.

FSDs must allow seeks to positions beyond end-of-file.

The information passed in IOflag is what was set for the handle during a DosOpen/DosOpen2 operation, or by a DosSetFHandState call.