Compatibility: 4.0+

Expects: AH    6cH

BX    extended open mode flags (see below)

CX    file attribute (used only if file gets created)

DX    action: 00-0h = if file exists, fail the call

00-1h = if file exists, open it

00-2h = if file exists, replace and open it

000-h = if doesn't exist, fail the call

001-h = if doesn't exist, create and open it

DS:SI address of an ASCIIZ  string of a filespec to open

Returns: AX    error code if CF is set to CY

file handle if no error

CX    action taken: 0 file was opened

1 file was created and opened

2 file was replaced and opened

Info: This function opens (or creates and opens) a file.  Think of it

as a smart 3dH Open which can optionally 3cH Create the file if

it doesn't exist.

Additionally, this call can disable normal INT 24h critical error

handling and can force all writes to go direct to the disk.

DS:DX points to an ASCIIZ string in the form...

d:\path\filename.ext0

If the drive or path is omitted, defaults are assumed.

BX On entry, BX contains extended mode flags as follows:

1 1 1 1 1 1

 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0        See Open Mode for more

 0 d f 0 0 0 0 0 i  shr  0  r/w         info on bits 0-7

                                  bits

                                0-2: read/write access mode

                                4-6: sharing mode

                                  7: inheritance

                                 13: 0=normal INT 24H use

                                     1=fail critical errors

                                       on open and all I/O

                                 14: 0=normal file buffering

1=directly to disk

If bit 13 is set (2000H), then I/O through this handle will never

cause an INT 24H critical error.  If a drive door is open (etc.),

then the function which caused the error will fail with a regular

DOS error.  Use Fn 59H to find out what happened.

If bit 14 is set (4000H), then the normal DOS output buffering is

bypassed and all output goes directly to the disk (as if you had

called Fn 68H after each write).  This can hurt I/O performance,

but it maximizes safety.

CX When creating a new file, set CX to the desired  file attribute

(read-only, hidden, etc.).  Use 0000H for normal files.  If the

file exists, CX is ignored.

DX This controls the open/create action, depending upon whether the

file exists at the time of the call.  Common combinations are:

0001H = open the file if it exists; otherwise fail the call

0011H = open the file if it exists; otherwise create it

0012H = if the file exists open and truncate it to length 0;

otherwise create it and open it

Notes:   Perhaps the most useful feature here is the ability to avoid

special handling for INT 24H critical errors.  Of course, you

can only discard your INT 24H handler if you are sure that the

application is used only under DOS 4.0+.

See Also: Handle-Oriented File I/O

INT 24H

DOS Functions

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