Function 23h Get File Size

mov dx, seg FileFCB

mov ds, dx

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

mov ah, 23h ;Get File Size

int 21h

cmp al, 0 ;zero means success

jne error_handler

Get File Size (Function 23h) returns the number of records in a file specified by a file control block (FCB).

This function has been superseded by Move File Pointer (Function 42h).

Parameter

FileFCB

Points to an FCB structure that identifies the file to examine. The fcbDriveID, fcbFileName, and fcbExtent fields must contain the filename information. Also, the fcbRecSize field must contain the size of a single file record. Other fields should contain 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 function is successful, the AL register contains 00h, and the fcbRandomRecNo field contains the number of records in the file. Otherwise, the AL register contains 0FFh.

Comment

MS-DOS returns the size of the file in records by dividing the size in bytes by the size of a single record (as specified by the fcbRecSize field). If the fcbRecSize field in the FCB structure is set to 1 byte, MS-DOS returns the size of the file in bytes.