Q42662: Corrupt Parameters in SUB Using PRINT with Comma; BC.EXE 4.50

Article: Q42662
Product(s): See article
Version(s): 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890309-98 buglist4.50 | mspl13_basic
Last Modified: 14-FEB-1991

In the example below, parameters that are passed to a SUBprogram and
printed out with a comma separating them will be corrupted within the
SUBprogram. This problem occurs only when the program has been
compiled to an EXE file. Altering the compile switches does not change
the incorrect results.

The program below demonstrates this problem. The problem exists only
when the parameters have been passed to a SUBprogram and are compiled
to an EXE file.

This problem occurs in .EXE programs only in QuickBASIC version 4.50.
Microsoft is researching this problem and will post new information
here as it becomes available. Previous versions of QuickBASIC, and
Microsoft BASIC Compiler versions 6.00, 6.00b, and 7.00, produce the
correct results (fixlist6.00 fixlist6.00b fixlist7.00).

The following program is TEST.BAS, which creates two variables and
passes them to a subroutine. The subroutine then prints the variables.

   DECLARE SUB test (a, b)
   a = 1
   b = 2
   CALL test(a, b)
   PRINT a, b

   SUB test (a, b)
      PRINT a, b
      b = 100
      PRINT a, b   ' This prints incorrectly.
      b = 256
   END SUB

The compiled EXE file prints the following incorrect output:

   1             2
   1             3.363116E-44
   1             100

If any PRINT statement is altered (for example, the first "PRINT a, b"
in the SUB is changed to a "PRINT a; b"), or if the program is run
from the QB.EXE environment, the correct output will be produced, as
follows:

   1             2
   1             100
   1             256

Another workaround for the problem is to compile with BC /X, or to add
"ON ERROR GOTO label" and "RESUME" statements to the program.

Another workaround is to assign a local variable to the passed
variable and then print the local variable instead of the passed
variable, for example:

   SUB test (a, b)
      x = a  ' Assign passed parameter to local variable.
      y = b  ' Assign passed parameter to local variable.
      PRINT x, y
      y = 100
      PRINT x, y   ' This prints correctly.
      y = 256
      a = x  ' Pass back values to parameters
      b = y  ' Pass back values to parameters
   END SUB

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