KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q42324: Period in Name of NAMED COMMON Can Erase BLANK COMMON Values

Article: Q42324
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom buglist4.00 buglist4.00b buglist4.50 | mspl13_basic
Last Modified: 26-FEB-1990

The following information applies to the QB.EXE editor in Microsoft
QuickBASIC Versions 4.00, 4.00b, and 4.50 and to QB.EXE in Microsoft
BASIC Compiler Versions 6.00 and 6.00b.

When CHAINing between two programs that contain COMMON blocks, the
values are not passed under the following conditions:

1. Both programs contain at least one blank and one named COMMON
   block.

2. The program being CHAINed to contains an additional COMMON block
   with variables declared as a user-defined TYPE.

3. The "Names" of the named COMMON blocks contain periods.

The COMMON values are passed correctly if the periods are removed from
the names in the COMMON blocks, or if the additional COMMON block with
a user-defined TYPE is removed.

This problem occurs only when running the programs from within the
QB.EXE environment. It does not occur when the programs are run as
compiled programs.

Microsoft has confirmed this to be a problem in QuickBASIC Versions
4.00, 4.00b, and 4.50, and in QB.EXE in Microsoft BASIC Compiler
Versions 6.00 and 6.00b (buglist6.00, buglist6.00b). The problem was
corrected in QBX.EXE in Microsoft BASIC Professional Development
System (PDS) Version 7.00 (fixlist7.00).

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

If the following program is run inside the QuickBASIC environment,
the values in the blank COMMON block are not passed to PROGRAM #2.
If the COMMON block name /named.block1/ is changed to /namedblock1/
or the COMMON block following the user-defined TYPE in PROGRAM #2 is
removed, then the values are passed correctly, as follows:

'PROGRAM #1
'
COMMON SHARED a1%, a2&, a3!, a4#
COMMON SHARED /named.block1/ b1%, b2&, b3!, b4#

CLS
a1% = 1: a2& = 64000: a3! = 1.5: a4# = 64000.5
CHAIN "prog2.bas"
END

'PROGRAM #2
'
TYPE UserDefinedType
  c1 AS INTEGER
  c2 AS INTEGER
END TYPE
COMMON SHARED a1%, a2&, a3!, a4#
COMMON SHARED /named.block1/ b1%, b2&, b3!, b#
COMMON SHARED /namedblock2/ var1 AS UserDefinedType

PRINT a1%, a2&, a3!, a4#
END

To prevent this problem, and to follow a good general rule, use only a
period in a name when accessing a field of a variable that is
DIMensioned as a user-defined TYPE.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.