INT 21 - DOS 2+ - "OPEN" - OPEN EXISTING FILE AH = 3Dh AL = access and sharing modes (see #01402) DS:DX -> ASCIZA NUL-terminated ASCII string. The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h. Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. filename CL = attribute mask of files to look for (server call only) Return: CF clear if successful AX = file handle CF set on error AX = error code (01h,02h,03h,04h,05h,0Ch,56h) (see #01680 at AH=59h) Notes: file pointer is set to start of file if SHARE or a network is loaded, the file open may fail if the file is already open, depending on the combination of sharing modes (see #01403,#01404) file handles which are inherited from a parent also inherit sharing and access restrictions files may be opened even if given the hidden or system attributes under the FlashTek X-32 DOS extender, the pointer is in DS:EDX DR DOS checks the system password or explicitly supplied password at the end of the filename (following a semicolon) against the reserved field in the directory entry before allowing access sharing modes are only effective on local drives if SHARE is loaded BUG: Novell DOS 7 SHARE v1.00 would refuse file access in the cases in #01403 marked with [1] (read-only open of a read-only file which had previously been opened in compatibility mode); this was fixed in SHARE v1.01 of 09/29/94 SeeAlso: AH=0Fh,AH=3Ch,AX=4301h,AX=5D00h,INT 2F/AX=1116h,INT 2F/AX=1226h Bitfields for access and sharing modes: Bit(s) Description (Table 01402) 2-0 access mode 000 read only 001 write only 010 read/write 011 (DOS 5+ internal) passed to redirector on EXEC to allow case-sensitive filenames 3 reserved (0) 6-4 sharing mode (DOS 3.0+) (see #01403) 000 compatibility mode 001 "DENYALL" prohibit both read and write access by others 010 "DENYWRITE" prohibit write access by others 011 "DENYREAD" prohibit read access by others 100 "DENYNONE" allow full access by others 111 network FCBsee File Control Block (only available during server call) 7 inheritance if set, file is private to current process and will not be inherited by child processes SeeAlso: #01782,#01403 (Table 01403) Values of DOS 2-6.22 file sharing behavior: | Second and subsequent Opens First |Compat Deny Deny Deny Deny Open | All Write Read None |R W RW R W RW R W RW R W RW R W RW - - - - -| - - - - - - - - - - - - - - - - - Compat R |Y Y Y N N N 1 N N N N N 1 N N W |Y Y Y N N N N N N N N N N N N RW|Y Y Y N N N N N N N N N N N N - - - - -| Deny R |C C C N N N N N N N N N N N N All W |C C C N N N N N N N N N N N N RW|C C C N N N N N N N N N N N N - - - - -| Deny R |2 C C N N N Y N N N N N Y N N Write W |C C C N N N N N N Y N N Y N N RW|C C C N N N N N N N N N Y N N - - - - -| Deny R |C C C N N N N Y N N N N N Y N Read W |C C C N N N N N N N Y N N Y N RW|C C C N N N N N N N N N N Y N - - - - -| Deny R |2 C C N N N Y Y Y N N N Y Y Y None W |C C C N N N N N N Y Y Y Y Y Y RW|C C C N N N N N N N N N Y Y Y Legend: Y = open succeeds, N = open fails with error code 05h C = open fails, INT 24 generated 1 = open succeeds if file read-only, else fails with error code 2 = open succeeds if file read-only, else fails with INT 24 SeeAlso: #01636,#01404 (Table 01404) Values for DOS 7.x file sharing behavior: | Second and subsequent Opens First |Compat Deny Deny Deny Deny Open | All Write Read None |R W RW A R W RW A R W RW A R W RW A R W RW A - - - - -| - - - - - - - - - - - - - - - - - - - - - - - - Compat R |Y Y Y Y N N N N Y N N Y N N N Y Y N N Y W |Y Y Y C N N N N N N N N N N N Y Y N N Y RW|Y Y Y C N N N N N N N N N N N Y Y N N Y NA|Y C C Y N N N N Y N N Y N N N Y Y N N Y - - - - -| Deny R |C C C C N N N N N N N N N N N N N N N N All W |C C C C N N N N N N N N N N N N N N N N RW|C C C C N N N N N N N N N N N N N N N N NA|C C C C N N N N N N N N N N N N N N N N - - - - -| Deny R |Y C C Y N N N N Y N N Y N N N Y Y N N Y Write W |C C C C N N N N N N N N Y N N Y Y N N Y RW|C C C C N N N N N N N N N N N Y Y N N Y NA|Y C C Y N N N N Y N N Y N N N Y Y N N Y - - - - -| Deny R |C C C C N N N N N Y N N N N N N N Y N N Read W |C C C C N N N N N N N N N Y N N N Y N N RW|C C C C N N N N N N N N N N N N N Y N N NA|Y Y Y Y N N N N Y Y Y Y N N N Y Y Y Y Y - - - - -| Deny R |Y Y Y Y N N N N Y Y Y Y N N N Y Y Y Y Y None W |C C C C N N N N N N N N Y Y Y Y Y Y Y Y RW|C C C C N N N N N N N N N N N Y Y Y Y Y NA|Y Y Y Y N N N N Y Y Y Y N N N Y Y Y Y Y Legend: R -> reading, W -> writing, RW -> both reading & writing, A/NA -> reading without access time update Y = open succeeds, N = open fails with error code 05h C = open fails, INT 24 generated SeeAlso: #01403,#01636