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Q50220: QB.EXE 4.50 "String Space Corrupt" Passing Function to .QLB

Article: Q50220
Product(s): See article
Version(s): 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S891006-116 buglist4.50 B_BasicCom | mspl13_basic
Last Modified: 26-FEB-1990

There is a problem in the QuickBASIC Version 4.50 environment with
passing a FUNCTION procedure as a parameter to a user-defined function
that calls a SUBprogram when the FUNCTION and SUBprogram procedures
are located in a Quick library. A "String space corrupt" error
displays, and the program returns to DOS. This problem occurs only
when running the program a second time [using any combination of the
ALT+R+R (Restart), F8, F5 (ALT+R+N), or SHIFT+F5 (ALT+R+S) (Start)
keys]. The problem doesn't occur in compiled .EXE programs.

Microsoft has confirmed this to be a problem in the QuickBASIC
environment (QB.EXE) in Version 4.50. This problem was corrected in
the QBX.EXE environment of Microsoft BASIC Professional Development
System (PDS) Version 7.00 for MS-DOS and MS OS/2 (fixlist7.00).

You can work around this problem by assigning the value returned by
the BN$ FUNCTION to a temporary value and passing this temporary value
when you invoke the FNOPEN% user-defined function (as demonstrated in
MAIN.BAS below).

The "String space corrupt" error is not generated in any of the
following cases:

1. If QLIB.BAS (shown below) is loaded as a secondary module instead
   of as a .QLB (Quick library)

2. When the two modules (shown below) are compiled into an .EXE (using
   QLIB.LIB or QLIB.OBJ) and run as an .EXE

3. When QuickBASIC Version 4.00 or 4.00b is used

The following programs, MAIN.BAS and QLIB.BAS, demonstrate the
problem. MAIN.BAS is the module loaded into the environment, and
QLIB.BAS is the Quick library, which is loaded in with the /L
invocation switch (for example, QB MAIN /L QLIB).

MAIN.BAS
--------

DECLARE FUNCTION BN$ (X$)
DECLARE SUB SOPEN (KAN%, K$, BEST$, RECL%)

DEF FNOPEN% (KAN%, K$, BEST$, RECL%)
     CALL SOPEN(KAN%, K$, BEST$, RECL%)
END DEF

CLS : LOCATE 21, 1

'Statement that causes the "String space corrupt" error:
FS% = FNOPEN%(2, "S", BN$("XXXXACTR"), 256)

'Workaround to eliminate the "String space corrupt" error:
'TEMP$ = BN$("XXXXACTR")
'FS% = FNOPEN%(2, "S", TEMP$, 256)

QLIB.BAS
--------

DECLARE FUNCTION BN$ (X$)
DECLARE SUB SOPEN (KAN%, K$, BEST$, RECL%)
FUNCTION BN$ (X$)
     BN$ = "C:0001" + MID$(X$, 5)
END FUNCTION
SUB SOPEN (KAN%, K$, BEST$, RECL%)
     PRINT BEST$
END SUB

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