DosProtectSetFilePtr

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Description

Moves the read or 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. */
FHLOCK    fhFileHandleLockID;  /*  The filehandle lockid returned by
                                   a previous DosProtectOpen. */
APIRET    ulrc;                /*  Return Code. */

ulrc = DosProtectSetFilePtr(hFile, ib, method, ibActual, fhFileHandleLockID);

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.
This field specifies the location in the file at which the read/write pointer starts before adding the ib offset. The values and their meanings are as shown in the following list:
FILE_BEGIN Move the pointer from the beginning of the file.
FILE_CURRENT Move the pointer from the current location of the read/write pointer.
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.
fhFileHandleLockID (FHLOCK) - input 
The filehandle lockid returned by a previous DosProtectOpen.

Return Code

ulrc (APIRET) - returns

DosProtectSetFilePtr 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. DosProtectSetFilePtr cannot be used to move to a negative position in the file.

DosProtectSetFilePtr cannot be used for a character device or pipe.

Example Code

This example opens or creates and opens a file named "DOSPROT.DAT", writes a string to it, returns the file pointer to the beginning of the file, reads it, and finally closes it using DosProtect functions.

#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;
   ULONG  ulAction       = 0;
   ULONG  ulBytesRead    = 0;
   ULONG  ulWrote        = 0;
   ULONG  ulLocal        = 0;
   UCHAR  uchFileName[20]  = "dosprot.dat",
          uchFileData[100] = " ";
   FHLOCK FileHandleLock = 0;        /* File handle lock   */
   APIRET rc             = NO_ERROR; /* Return code */

   /* Open the file test.dat.  Make it read/write, open it */
   /* if it already exists and create it if it is new.     */
   rc = DosProtectOpen(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   */
                &FileHandleLock);               /* File handle lock id     */
   if (rc != NO_ERROR) {
      printf("DosProtectOpen error: return code = %u\n", rc);
      return 1;
   } else {
     printf ("DosProtectOpen: Action taken = %u\n", ulAction);
   } /* endif */

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

   rc = DosProtectWrite (hfFileHandle,       /* File handle                  */
                  (PVOID) uchFileData,       /* String to be written         */
                  sizeof (uchFileData),      /* Size of string to be written */
                  &ulWrote,                  /* Bytes actually written       */
                  FileHandleLock);           /* File handle lock id          */
   if (rc != NO_ERROR) {
      printf("DosProtectWrite error: return code = %u\n", rc);
      return 1;
   } else {
      printf ("DosProtectWrite: Bytes written = %u\n", ulWrote);
   } /* endif */

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

   /* Read the first 100 bytes of the file */
   rc = DosProtectRead (hfFileHandle,         /* File Handle                 */
                 uchFileData,                 /* String to be read           */
                 100L,                        /* Length of string to be read */
                 &ulBytesRead,                /* Bytes actually read         */
                 FileHandleLock);             /* File handle lock id         */
   if (rc != NO_ERROR) {
      printf("DosProtectRead error: return code = %u\n", rc);
      return 1;
   } else {
      printf("DosProtectRead: Bytes read = %u\n%s\n", ulBytesRead, uchFileData);
   } /* endif */

   rc = DosProtectClose(hfFileHandle, FileHandleLock);   /* Close the file */
   if (rc != NO_ERROR) {
      printf("DosProtectClose error: return code = %u\n", rc);
      return 1;
    }
   return NO_ERROR;
}

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