Function 0Fh (15)        Open File, Using FCBs

Open an existing file using a File Control Block (FCB).

On entry:      AH         0Fh
DS:DX      Pointer to an unopened FCB

Returns:       AL         00h       If file successfully opened
FFh       If file not found

                                                                          

The FCB is initialized as follows:

Offset  Length  Field           Initialized to       Initialized by

00h     1     Drive code      Drive specified           User
01h     8     Filename        Filename                  User
09h     3     Extension       Filename extension        User
0Ch     2     Current Block   00h                       DOS
0Eh     2     Record Size     80h                       DOS; see below
10h     4     File Size       Value in file directory   DOS
14h     2     Date            Value in file directory   DOS
16h     2     Time            Value in file directory   DOS
18h     8     Reserved
20h     1     Current Record  See notes below           User
21h     4     Random Record   See notes below           User
Number

An extended File Control Block is used to access files with special
attributes. An extended File Control Block has three additional
fields, starting at offset -07h (minus 7), as follows:

Offset  Length  Field             Initialized to     Initialized by

-07h     1     Extended FCB ID   FFh                     User
-06h     5     Reserved          Must be zeros           User
-01h     1     Attribute Byte    File attribute          User


Notes:         If the drive code was 0 (default drive), this
function changes it to the current default drive,
where A = 1, B = 2, etc.

The record-size field is set by DOS to 80h (128)
bytes. If you want to use a different value, change
the field after the file has been opened and before
you perform any disk operation. If the record size
is less than 64 bytes, all four bytes of this field
are used; otherwise only the lower three bytes are
used.

The current record field is used for sequential
read/write operations, and must be set before
performing any sequential read/writes. Set the
current record field to the record number that you
wish to access within the current block. The current
record field can take on any value between 0 and
127.

The random record number field must be set before
any random read/write operations can be performed.
Set this field to the record number relative to the
beginning of the file that you wish to access.

File Control Blocks are a holdover from DOS 1. It is
preferable to manipulate files using the newer DOS
services that deal with files via handles. (All file
functions above 2Eh use handles rather than FCBs.)


See also:   Interrupt 20098     (Destroy Disk and Exit)
Service 23512       (Memorial Service for Dead Disk)

See also: FCB
See also: 3Dh
See also: 10h
See also: 29h

0Fh (15) Open File, Using FCBs