Q31426: "Duplicate Definition" on STATIC Array in Second CALL to SUB

Article: Q31426
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr B_BasicCom | mspl13_basic
Last Modified: 28-DEC-1989

In the following sources, the example of using the STATIC statement
does not clearly explain what will happen with a second call to the
SUB:

1. Page 80 of the "Microsoft QuickBASIC 4.0: Programming in BASIC:
   Selected Topics" manual for Versions 4.00 and 4.00b

2. Page 70 of the "Microsoft QuickBASIC: Programming in BASIC" manual
   for Version 4.50

If SubProg2 is called more than once, the DIM statement gives you a
"Duplicate Definition" error message. This is because in a recursive
procedure, arrays are always dimensioned dynamically (that is, at run
time), and making the array retain its values between calls (with the
STATIC statement) means that the array was already dimensioned at the
second call.

The example should be changed as follows:

1. Declare an additional STATIC variable as a flag.

2. Put the DIM in an IF...END IF block that executes only upon first
   call to the routine, and not on subsequent calls, as determined by
   the flag variable.

This correction also applies to the following:

1. Page 80 of "Microsoft BASIC Compiler Version 6.00 for MS OS/2 and
   MS-DOS: Programming in BASIC: Selected Topics" for the BASIC
   compiler Versions 6.00 and 6.00b

2. Page 66 of "Microsoft BASIC 7.0: Programmer's Guide" for Microsoft
   BASIC PDS Version 7.00 for MS-DOS and MS OS/2

Removing the array from the STATIC statement also eliminates the
"Duplicate Definition."

The following code demonstrates how to avoid the "Duplicate
Definition" error:

DECLARE SUB dummy ()
PRINT "call the subroutine"
CALL dummy
PRINT "call the routine again"
CALL dummy

SUB dummy
STATIC a(), FirstPassFlag   ' STATIC retains values between CALLs
' FirstPassFlag assures that array gets DIMensioned only once.
IF FirstPassFlag = 0 THEN
   DIM a(1)
   FirstPassFlag = 1
END IF
print "continuing on"
END SUB

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