FS CHGFILEPTR: Difference between revisions

Latest revision as of 01:28, 9 February 2020

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.

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.

@@ Line 1: / Line 1: @@
-Move a file's logical read/write position pointer.
+{{DISPLAYTITLE:FS_CHGFILEPTR}}
+Move a file's logical read/write position pointer.
 ==Syntax==
   FS_CHGFILEPTR(psffsi, psffsd, offset, type, IOflag)
 ==Parameters==
-;psffsi
+;psffsi:Is a pointer to the file-system-independent portion of an open file instance.
-: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.
-: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.
+;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.
-;psffsd
+:type == 0 indicates seek relative to beginning of file.
-: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.
+:type == 1 indicates seek relative to current position within the file.
+:type == 2 indicates seek relative to end of file.
-;offset
+:The value of type passed to the FSD will be valid.
-:Is the signed offset to be added to the current file size or position to form the new position within the file.
+;IOflag:Indicates information about the operation on the handle.
+:IOflag == 0x0010 indicates write-through.
-;type
+:IOflag == 0x0020 indicates no-cache.
-: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==
+Calling Sequence
-==Sample==
-Calling Sequence
 <PRE>
 int far pascal FS_CHGFILEPTR(psffsi, psffsd, offset, type, IOflag)
@@ Line 40: / Line 29: @@
 unsigned short IOflag;
 </PRE>
 ==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.
+The information passed in IOflag is what was set for the handle during a DosOpen/DosOpen2 operation, or by a [[DosSetFHandState]] call.
 [[Category:IFS Interfaces]]
-{{DISPLAYTITLE:FS_CHGFILEPTR}}