Function 0Fh Open File with FCB

mov dx, seg FileFCB

mov ds, dx

mov dx, offset FileFCB ;ds:dx points to FCB

mov ah, 0Fh ;Open File with FCB

int 21h

cmp al, 0 ;zero means success

jne error_handler

Open File with FCB (Function 0Fh) opens a file identified by the file control block (FCB).

This function has been superseded by Open File with Handle (Function 3Dh).

Parameter

FileFCB

Points to an FCB structure that identifies the file to open. The fcbDriveId, fcbFileName, and fcbExtent fields must specify the filename and drive; all other fields must be set to zero. The FCB structure has the following form:

FCB STRUC

fcbDriveID db ? ;drive no. (0=default, 1=A, etc.)

fcbFileName db '????????' ;filename

fcbExtent db '???' ;file extension

fcbCurBlockNo dw ? ;current block number

fcbRecSize dw ? ;record size

fcbFileSize db 4 dup (?) ;size of file in bytes

fcbFileDate dw ? ;date file last modified

fcbFileTime dw ? ;time file last modified

fcbReserved db 8 dup (?) ;reserved

fcbCurRecNo db ? ;current record number

fcbRandomRecNo db 4 dup (?) ;random record number

FCB ENDS

For a full description of the FCB structure, see Chapter 3, “File System.”

Return Value

If the file is found, the AL register contains 00h and the remaining fields in the FCB structure are filled in. Otherwise, the AL register contains 0FFh.

Comments

This function does not support paths, so it is possible to open only files in the current directory.

If the calling program specifies zero for the drive number, MS-DOS searches for the file on the default drive. If the system finds the file, it fills in the fcbDriveId field with the correct drive.

When a file is opened, MS-DOS sets the current block number in the FCB to zero (the file pointer is at the beginning of the file).

MS-DOS initially sets the record size to 128 bytes. If some other record size is to be used, the size must be set after the call to Open File with FCB but before any other disk operation.