DosSetFilePtrL: Difference between revisions

Revision as of 01:09, 17 November 2016

Description

DosSetFilePtrL moves the read write pointer according to the type of move specified.

Syntax

#define INCL DOSFILEMGR
#include  os2.h 

    APIRET DosSetFilePtrL
        (HFILE hFile, LONGLONG ib, ULONG method, PLONGLONG ibActual)

Parameters

hFile HFILE) input

The handle returned by a previous DosOpenL function.

ib LONGLONG) 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:

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 PLONGLONG) output: Address of the new pointer location.

Return Code

ulrc APIRET) returns

DosSetFilePtrL returns one of the following values:

0 NO_ERROR
ERROR_INVALID_FUNCTION
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 64-bit number. A negative value for ib moves the pointer backward in the file; a positive value moves it forward. DosSetFilePtrL cannot be used to move to a negative position in the file.

DosSetFilePtrL 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 DosOpenL */
ULONG  ulBytesRead    = 0;      /* Number of bytes read by DosRead */
ULONG  ulWrote        = 0;      /* Number of bytes written by DosWrite */
LONGLONG  ullLocal    = 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 = DosOpenL(uchFileName,                    /* File path name */
 hfFileHandle,                  /* File handle */
 ulAction,                      /* Action taken */
(LONGLONG)100,                  /* 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("DosOpenL error  return code = %u\n", rc);
return 1;
  else  
printf ("DosOpenL  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 = DosSetFilePtrL (hfFileHandle,           /* File Handle */
(LONGLONG)0,            /* Offset */
FILE_BEGIN,             /* Move from BOF */
 ullLocal);             /* New location address */
if (rc != NO_ERROR)  
printf("DosSetFilePtrL 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;

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