Error handling

 BBS: Inland Empire Archive
Date: 07-08-92 (22:44)             Number: 272
From: MATT HART                    Refer#: NONE
  To: BILL CAMPBELL                 Recvd: NO  
Subj: Error handling                 Conf: (2) Quik_Bas

 BC> handling and recompiled (using /e and /x) and found that those 8
 BC> lines of code cost me about an extra 10k. All I want to do is
 BC> trap for a file not being there when I try to open it.

All you need is /X - /E is for trapping without resume, /X
handles with or without.  You should make a seperate .BAS
program, and link with it.  Here's also a way to do it with
an interrupt call:

'
' EXIST.BAS  by Matt Hart
' Uses Interrupt 21H to see if a file exists.
'
    DEFINT A-Z
    TYPE RegTypeX
        ax    AS INTEGER
        bx    AS INTEGER
        cx    AS INTEGER
        dx    AS INTEGER
        bp    AS INTEGER
        si    AS INTEGER
        di    AS INTEGER
        flags AS INTEGER
        ds    AS INTEGER
        es    AS INTEGER
    END TYPE
    DECLARE FUNCTION Exist(File$)
    File$="EXIST.BAS"
    File$=command$
    Print Exist(File$)
    END
FUNCTION Exist(File$)
    DIM InRegs as RegTypeX
    DIM OutRegs as RegTypeX
    DIM DTA as string * 42
    DIM F as string * 64
    InRegs.AX = &H1A00
    InRegs.DS = VARSEG(DTA)
    InRegs.DX = VARPTR(DTA)
    CALL InterruptX (&H21, InRegs, OutRegs)
    F = File$+CHR$(0)
    InRegs.AX = &H4E00
    InRegs.CX = 0
    InRegs.DS = VARSEG(F)
    InRegs.DX = VARPTR(F)
    CALL InterruptX (&H21, InRegs, OutRegs)
    if OutRegs.AX = 2 or OutRegs.AX = 18 then
        Exist = 0
    else
        Exist = -1
    endif
END FUNCTION


Without an interrupt call (and typed without testing!):

     ON ERROR GOTO ErrorTrap
FUNCTION Exist(File$)
     SHARED Ecode
     Ecode = -1                    ' Assume it exists
     Fil = FREEFILE
     OPEN File$ FOR INPUT AS Fil
     CLOSE Fil                     ' code goes here if file exists AND
     Exist = Ecode                 ' after the errortrap
     ON ERROR GOTO 0               ' trapping OFF
END FUNCTION

ErrorTrap:
     Ecode = 0           ' code goes here after the OPEN if it doesn't exist
     RESUME NEXT         ' continue at the close

~~
---
 * Origin: Midnight Micro!  V.32/REL  (918)451-3306 (1:170/600)