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Q34682: Communications (COM1:, COM2:) Receive Buffer Lost During CHAIN

Article: Q34682
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: 8-FEB-1990

The communications receive buffer is cleared when chaining to another
module; at this point, data can be lost. This problem occurs only in a
compiled .EXE program, and does not occur in the QB.EXE editor.
Compiling with the BC /d (debug) option does not help. Data received
at the communications port after the CHAIN operation is received
normally.

Microsoft has confirmed this to be a problem in Microsoft QuickBASIC
Versions 4.00, 4.00b, and 4.50, and in Microsoft BASIC Compiler
Versions 6.00 and 6.00b for MS-DOS and MS OS/2 (buglist6.00,
buglist6.00b). This problem was corrected in Microsoft BASIC
Professional Development System (PDS) Version 7.00 (fixlist7.00).

The programs below demonstrate the problem:

   ' File: P1.BAS
   OPEN "com1:1200,e,7,1,cs,ds" FOR RANDOM AS #2
   for x=1 to 10000 :next
   y=loc(2)
   print y;
   CHAIN "p2"    'Chain to second program and print out buffer size

   ' File: P2.BAS
   a$=input$(loc(2),2)
   print a$;

   ' File:P.bas
   'This program will send the characters
   open "com1:1200,e,7,1,cs,ds" for random as #1
   print "start"
   for x=1 to 10000
   print #1, x;
   next x
   close #1

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