Changing a Drive's Volume Label

• Microsoft C for MS-DOS, version 5.1

SUMMARY

Changing a drive's volume label involves the use of FCB (file control block) file processing, and therefore is not supplied with the C run-time libraries. However, one of the ways to do this is through MS-DOS Interrupt 21h calls for FCB file manipulation.

MORE INFORMATION

Below is an assembly routine written with Microsoft MASM version 5.1 to change a drive's volume name. To do this, it first sets up an extended FCB to allow for manipulating files with attributes. Offset 6 of the FCB is set to 8 (_A_VOLID defined in DOS.H) to specify a volume. The old volume is searched for with "*.*" as a pattern and deleted, then the volume is re-created with the new volume label passed by the C caller. The function returns the error code supplied from the MS-DOS application programming interface (API) that creates the volume label.

Use the following:

   rc = NewVol( iDrive, szName ); // iDrive = Drive number ( 1, 2, ... )
                                  // szName = Up to 11 chars. DOS filename
                                  // rc = Return Code from function.

Sample Code

; unsigned NewVol( int, char * ) will delete a disk volume and

;                                  create one with the new name.
;

;               /Dlang={C FORTRAN BASIC PASCAL}

.DATA

maxlen  EQU     11                 ;Maximum name length
datasz  EQU      2                 ;Size of Data Pointers

fcb     DB      255, 0, 0, 0, 0, 0, 8, 1
        DB      37 DUP (?)
default DB      '*       *  '      ;Equivalent to "*.*"

        mov     bx,Drive           ;Get drive number ( 1 byte )
        mov     fcb+7,bl           ;...and store in FCB offset 7
        mov     ax,ds
        mov     es,ax
        cld                        ;Upward move
        mov     cx,maxlen          ;Size of move
        mov     si,OFFSET default  ;Source string to
        mov     di,OFFSET fcb+8    ;...filename offset in 8 FCB
        rep     movsb              ;Move maxlen bytes of vol name
        mov     dx,OFFSET fcb      ;Delete volume off drive
        mov     ah,13H
        int     21H
        mov     cx,maxlen
        mov     si,VolName         ;New name passed by C caller
        mov     di,OFFSET fcb+8
        rep     movsb              ;Copy 11 chars for new label
        mov     dx,OFFSET fcb      ;Create the new volume
        mov     ah,16H
        int     21H
        mov     dx,OFFSET fcb      ;Close the file
        mov     ah,10H
        int     21H
        mov     ah,0
        ret

        END