Difference between revisions of "DosProtectSetFilePtr"
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Moves the read or write pointer according to the type of move specified. | Moves the read or write pointer according to the type of move specified. | ||
==Syntax== | ==Syntax== | ||
− | + | DosProtectSetFilePtr(hFile, ib, method, ibActual, fhFileHandleLockID) | |
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==Parameters== | ==Parameters== | ||
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::FILE_END Move the pointer from the end of the file. Use this method to determine a file's size. | ::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. | ;ibActual (PULONG) - output : Address of the new pointer location. | ||
− | ;fhFileHandleLockID (FHLOCK) - input : The filehandle lockid returned by a previous DosProtectOpen. | + | ;fhFileHandleLockID (FHLOCK) - input : The filehandle lockid returned by a previous [[DosProtectOpen]]. |
==Return Code== | ==Return Code== | ||
− | + | ;ulrc (APIRET) - returns:DosProtectSetFilePtr returns one of the following values: | |
− | DosProtectSetFilePtr returns one of the following values: | + | |
* 0 NO_ERROR | * 0 NO_ERROR | ||
* 1 ERROR_INVALID_FUNCTION | * 1 ERROR_INVALID_FUNCTION |
Latest revision as of 06:49, 1 December 2019
Moves the read or write pointer according to the type of move specified.
Syntax
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; }