"Duplicate Definition" on STATIC Array in Second CALL to SUB (31426)

SUMMARY

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

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