Purpose
DosSetFilePtr moves the read write pointer according to the type of move specified.
Syntax
#define INCL DOSFILEMGR #include os2.h
APIRET DosSetFilePtr
Parameters
hFile HFILE) input
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
Move the pointer from the beginning of the file.
Move the pointer from the current location of the read write pointer.
Move the pointer from the end of the file. Use this method to determine a file s size.
Returns
ulrc APIRET) returns
DosSetFilePtr returns one of the following values
25
Remarks
The read/write pointer in a file is a signed 32-bit number. A negative value for ib moves the pointer backward; a positive value moves it forward. The resulting pointer value cannot be negative or larger than the disk or an error will be returned. The signed 32-bit value of the read/write pointer limits the raw file system to the first 2 Gigabytes of a disk.
Related Functions
Example Code
The following is NOT a complete usable program. It is simply intended to provide an idea of how to use Raw I/O File System APIs (e.g. DosOpen, DosRead, DosWrite, DosSetFilePtr, and DosClose).
This example opens physical disk #1 for reading and physical disk #2 for writing. DosSetFilePtr is used to set the pointer to the beginning of the disks. Using DosRead and DosWrite, 10 megabytes of data is transferred from disk #1 to disk #2. Finally, DosClosed is issued to close the disk handles.
It is assumed that the size of each of the two disks is at least 10 megabytes.
#define INCL_DOSFILEMGR /* Include File Manager APIs */#define INCL_DOSMEMMGR /* Includes Memory Management APIs */
#define INCL_DOSERRORS /* DOS Error values */
#include os2.h>
#include stdio.h>
#include string.h>
#define SIXTY_FOUR_K 0x10000
#define ONE_MEG 0x100000
#define TEN_MEG 10*ONE_MEG
#define UNC_DISK1 "\\\\.\\Physical_Disk1"
#define UNC_DISK2 "\\\\.\\Physical_Disk2"
int main(void) {
HFILE hfDisk1 = 0; /* Handle for disk #1 */
HFILE hfDisk2 = 0; /* Handle for disk #2 */
ULONG ulAction = 0; /* Action taken by DosOpen */
ULONG cbRead = 0; /* Bytes to read */
ULONG cbActualRead = 0; /* Bytes read by DosRead */
ULONG cbWrite = 0; /* Bytes to write */
ULONG ulLocation = 0;
ULONG cbActualWrote = 0; /* Bytes written by DosWrite */
UCHAR uchFileName1[20] = UNC_DISK1, /* UNC Name of disk 1 */
uchFileName2[20] = UNC_DISK2; /* UNC Name of disk 2 */
PBYTE pBuffer = 0;
ULONG cbTotal = 0;
APIRET rc = NO_ERROR; /* Return code */
/* Open a raw file system disk #1 for reading */
rc = DosOpen(uchFileName1, /* File name */
hfDisk1, /* File handle */
ulAction, /* Action taken by DosOpen */
0L, /* no file size */
FILE_NORMAL, /* File attribute */
OPEN_ACTION_OPEN_IF_EXISTS, /* Open existing disk */
OPEN_SHARE_DENYNONE | /* Access mode */
OPEN_ACCESS_READONLY,
0L); /* No extented attributes */
if (rc != NO_ERROR) {
printf("DosOpen error rc = %u\n", rc);
return(1);
} /* endif */
/* Set the pointer to the begining of the disk */
rc = DosSetFilePtr(hfDisk1, /* Handle for disk 1 */
0L, /* Offset must be multiple of 512 */
FILE_BEGIN, /* Begin of the disk */
ulLocation); /* New pointer location */
if (rc != NO_ERROR) {
printf("DosSetFilePtr error rc = %u\n", rc);
return(1);
} /* endif */
/* Open a raw file system disk #2 for writing */
rc = DosOpen(uchFileName2, /* File name */
hfDisk2, /* File handle */
ulAction, /* Action taken by DosOpen */
0L, /* no file size */
FILE_NORMAL, /* File attribute */
OPEN_ACTION_OPEN_IF_EXISTS, /* Open existing disk */
OPEN_SHARE_DENYNONE | /* Access mode */
OPEN_ACCESS_READWRITE,
0L); /* No extented attributes */
if (rc != NO_ERROR) {
printf("DosOpen error rc = %u\n", rc);
return(1);
} /* endif */
/* Set the pointer to the begining of the disk */
rc = DosSetFilePtr(hfDisk2, /* Handle for disk 1 */
0L, /* Offset must be multiple of 512 */
FILE_BEGIN, /* Begin of the disk */
ulLocation); /* New pointer location */
if (rc != NO_ERROR) {
printf("DosSetFilePtr error rc = %u\n", rc);
return(1);
} /* endif */
/* Allocate 64K of memory for transfer operations */
rc = DosAllocMem((PPVOID) pBuffer, /* Pointer to buffer */
SIXTY_FOUR_K, /* Buffer size */
PAG_COMMIT | /* Allocation flags */
PAG_READ |
PAG_WRITE);
if (rc != NO_ERROR) {
printf("DosAllocMem error rc = %u\n", rc);
return(1);
} /* endif */
cbRead = SIXTY_FOUR_K;
while (rc == NO_ERROR cbTotal TEN_MEG) {
/* Read from #1 */
rc = DosRead(hfDisk1, /* Handle for disk 1 */
pBuffer, /* Pointer to buffer */
cbRead, /* Size must be multiple of 512 */
cbActualRead); /* Actual read by DosOpen */
if (rc) {
printf("DosRead error return code = %u\n", rc);
return 1;
}
/* Write to disk #2 */
cbWrite = cbActualRead;
rc = DosWrite(hfDisk2, /* Handle for disk 2 */
pBuffer, /* Pointer to buffer */
cbWrite, /* Size must be multiple of 512 */
cbActualWrote); /* Actual written by DosOpen */
if (rc) {
printf("DosWrite error return code = %u\n", rc);
return 1;
}
if (cbActualRead != cbActualWrote) {
printf("Bytes read (%u) does not equal bytes written (%u)\n",
cbActualRead, cbActualWrote);
return 1;
}
cbTotal += cbActualRead; /* Update total transferred */
}
printf("Transfer successfully %d bytes from disk #1 to disk #2.\n",
cbTotal);
/* Free allocated memmory */
rc = DosFreeMem(pBuffer);
if (rc != NO_ERROR) {
printf("DosFreeMem error return code = %u\n", rc);
return 1;
}
rc = DosClose(hfDisk1);
if (rc != NO_ERROR) {
printf("DosClose error return code = %u\n", rc);
return 1;
}
rc = DosClose(hfDisk2);
if (rc != NO_ERROR) {
printf("DosClose error return code = %u\n", rc);
return 1;
}
return NO_ERROR;
}