Q32099: BC.EXE "Internal Error" Using Function as Argument to INSTR

Article: Q32099
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b fixlist4.50 B_BasicCom | mspl13_basic
Last Modified: 8-DEC-1989

If a function is used as an argument to the INSTR function and the
INSTR function is the expression in an ON <expression> GOTO statement,
the BC.EXE compiler will give an "internal error" message. This error
occurs with functions defined with the DEF FN method.

Compiling with the BC /D (debug) option does not correct the problem.

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

A workaround is to assign the result of the function to an
intermediate variable and to use that variable as the argument to the
function.

This problem does not occur with QuickBASIC Version 3.00 using DEF FN
functions. Please note that Version 3.00 does not support FUNCTION/END
FUNCTION statements.

The following code causes BC.EXE to generate an "internal error"
message:

          DEF FNT$(A$) = CHR$(ASC(A$) AND &H5F)
          B$ = "z"
          on  INSTR("XYZ", FNT$(B$)) goto 1000
        print
     1000 print "this is a test"

The following code works around the error:

          DEF FNT$(A$) = CHR$(ASC(A$) AND &H5F)
          B$ = "z"
           X$ = FNT$(B$)
          on  INSTR("XYZ", X$) goto 1000
    1000  print "this is a test"

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