Q42586: Variable with Periods in COMMON Block Can Cause Problems

Article: Q42586
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b buglist4.50 B_BasicCom | mspl13_basic
Last Modified: 26-FEB-1990

In the Microsoft QB.EXE editor, CHAINing between programs that have a
COMMON block can cause errors, under the following conditions:

1. The programs have a COMMON block.

2. The COMMON block contains an array, a user-defined TYPE variable,
   and a simple variable that contains one or more periods.

The result is an "array not defined" error message in the CHAINed-to
program. If the period(s) are removed from the simple variable, the
programs CHAIN and run correctly. This error occurs only when running
in the QB.EXE editor. The programs execute properly after being
compiled with BC.EXE.

Microsoft has confirmed this to be a problem in QuickBASIC Versions
4.00, 4.00b, and 4.50. This problem was corrected in Microsoft BASIC
Professional Development System (PDS) Version 7.00 (fixlist7.00).
Microsoft also recommends that you do not use periods in variable
names, since the period is now used to distinguish between
user-defined-TYPE variables. There may be conflicts between the two
usages.

In the following program examples, the COMMON block consists of an
integer array, a user-defined-TYPE variable, and a single-precision
variable. If PROG1.BAS is run inside the QuickBASIC environment, a
"Subscript out of range" error occurs in PROG2.BAS, on the PRINT
statement. This is because the array dimensions have not been
correctly passed in the COMMON block.

If the periods are removed from the variable x.to.y in PROG2.BAS, the
program executes normally. Also, if the programs are compiled as they
appear here with BC.EXE, they CHAIN together and run properly.

Code Example
------------

'----------------------------------- PROG1.BAS
'$DYNAMIC
TYPE test
  a AS INTEGER
  b AS INTEGER
END TYPE
COMMON SHARED c() AS INTEGER
COMMON SHARED Typed AS test
COMMON SHARED x.to.y
DIM SHARED c(1 TO 60) AS INTEGER

c(3) = 42
PRINT "Press a key to CHAIN to PROG2..."
WHILE INKEY$ = "": WEND
CHAIN "PROG2"
END

'----------------------------------- PROG2.BAS
'$DYNAMIC
TYPE test
  a AS INTEGER
  b AS INTEGER
END TYPE
COMMON SHARED c() AS INTEGER
COMMON SHARED Typed AS test
COMMON SHARED x.to.y

PRINT UBOUND(c), c(3)
END

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