DosSetFilePtr

Description

Moves the read/write pointer according to the type of move specified.

Syntax

#define INCL_DOSFILEMGR
#include <os2.h>

HFILE     hFile;     /*  The handle returned by a previous DosOpen function. */
LONG      ib;        /*  The signed distance (offset) to move, in bytes. */
ULONG     method;    /*  The method of moving. */
PULONG    ibActual;  /*  Address of the new pointer location. */
APIRET    ulrc;      /*  Return Code. */

ulrc = DosSetFilePtr(hFile, ib, method, ibActual);

Parameters

hFile (HFILE) - input

The handle returned by a previous DosOpen function.

ib (LONG) - input

The signed distance (offset) to move, in bytes.

method (ULONG) - input

The method of moving.

Specifies a location in the file from where the ib to move the read/write pointer starts. The values and their meanings are described in the following list:

0 FILE_BEGIN Move the pointer from the beginning of the file.

1 FILE_CURRENT Move the pointer from the current location of the read/write pointer.

2 FILE_END Move the pointer from the end of the file. Use this method to determine a file's size.

ibActual (PULONG) - output

Address of the new pointer location.

Return Code

ulrc (APIRET) - returns

DosSetFilePtr returns one of the following values:

• 0 NO_ERROR
• 1 ERROR_INVALID_FUNCTION
• 6 ERROR_INVALID_HANDLE
• 132 ERROR_SEEK_ON_DEVICE
• 131 ERROR_NEGATIVE_SEEK
• 130 ERROR_DIRECT_ACCESS_HANDLE

Remarks

The read/write pointer in a file is a signed 32-bit number. A negative value for ib moves the pointer backward in the file; a positive value moves it forward. DosSetFilePtr cannot be used to move to a negative position in the file.

DosSetFilePtr cannot be used for a character device or pipe.

Example Code

This example opens or creates and opens a file named "DOSTEST.DAT", writes to it, positions the file pointer back to the beginning of the file, reads from the file, and finally closes it.

#define INCL_DOSFILEMGR          /* File Manager values */
#define INCL_DOSERRORS           /* DOS Error values    */
#include <os2.h>
#include <stdio.h>
#include <string.h>

int main(void) {
   HFILE  hfFileHandle   = 0L;     /* Handle for file being manipulated */
   ULONG  ulAction       = 0;      /* Action taken by DosOpen */
   ULONG  ulBytesRead    = 0;      /* Number of bytes read by DosRead */
   ULONG  ulWrote        = 0;      /* Number of bytes written by DosWrite */
   ULONG  ulLocal        = 0;      /* File pointer position after DosSetFilePtr */
   UCHAR  uchFileName[20]  = "dostest.dat",     /* Name of file */
          uchFileData[100] = " ";               /* Data to write to file */
   APIRET rc             = NO_ERROR;            /* Return code */

   /* Open the file test.dat.  Use an existing file or create a new */
   /* one if it doesn't exist.                                      */
   rc = DosOpen(uchFileName,                    /* File path name */
                &hfFileHandle,                  /* File handle */
                &ulAction,                      /* Action taken */
                100L,                           /* File primary allocation */
                FILE_ARCHIVED | FILE_NORMAL,    /* File attribute */
                OPEN_ACTION_CREATE_IF_NEW |
                OPEN_ACTION_OPEN_IF_EXISTS,     /* Open function type */
                OPEN_FLAGS_NOINHERIT |
                OPEN_SHARE_DENYNONE  |
                OPEN_ACCESS_READWRITE,          /* Open mode of the file */
                0L);                            /* No extended attribute */
   if (rc != NO_ERROR) {
      printf("DosOpen error: return code = %u\n", rc);
      return 1;
   } else {
     printf ("DosOpen: Action taken = %ld\n", ulAction);
   } /* endif */

   /* Write a string to the file */
   strcpy (uchFileData, "testing...\n1...\n2...\n3\n");

   rc = DosWrite (hfFileHandle,                /* File handle */
                  (PVOID) uchFileData,         /* String to be written */
                  sizeof (uchFileData),        /* Size of string to be written */
                  &ulWrote);                   /* Bytes actually written */

   if (rc != NO_ERROR) {
      printf("DosWrite error: return code = %u\n", rc);
      return 1;
   } else {
      printf ("DosWrite: Bytes written = %u\n", ulWrote);
   } /* endif */

   /* Move the file pointer back to the beginning of the file */
   rc = DosSetFilePtr (hfFileHandle,           /* File Handle */
                       0L,                     /* Offset */
                       FILE_BEGIN,             /* Move from BOF */
                       &ulLocal);              /* New location address */
   if (rc != NO_ERROR) {
      printf("DosSetFilePtr error: return code = %u\n", rc);
      return 1;
   }

   /* Read the first 100 bytes of the file */
   rc = DosRead (hfFileHandle,                /* File Handle */
                 uchFileData,                 /* String to be read */
                 100L,                        /* Length of string to be read */
                 &ulBytesRead);               /* Bytes actually read */

   if (rc != NO_ERROR) {
      printf("DosRead error: return code = %u\n", rc);
      return 1;
   } else {
      printf ("DosRead: Bytes read = %u\n%s\n", ulBytesRead, uchFileData);
   } /* endif */

   rc = DosClose(hfFileHandle);                /* Close the file */

   if (rc != NO_ERROR) {
      printf("DosClose error: return code = %u\n", rc);
      return 1;
   }
   return NO_ERROR;
}

Related Functions

• DosOpen
• DosRead
• DosSetFileSize
• DosWrite