Q43930: Recursive Procedure Variables Not Saved When in COMMON

Article: Q43930
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890424-119 B_BasicCom | mspl13_basic
Last Modified: 15-DEC-1989

QuickBASIC procedures can recursively CALL themselves. Any needed
variables to be used in the recursive procedure should be passed as
parameters, and all local variables (variables dimensioned only in the
SUB itself) variables whose values need to be preserved through each
recursive CALL should be declared as STATIC. STATIC declaration causes
each variable's values to be retained on the stack for later use.

One important note is that all variables that are located in a COMMON
or COMMON SHARED block and are used in a recursive procedure will not
be saved through each recursive CALL.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
and 4.50 for MS-DOS, Microsoft BASIC Compiler Versions 6.00 and 6.00b
for MS-DOS and MS OS/2, and Microsoft BASIC PDS Version 7.00 for
MS-DOS and MS OS/2.

More information concerning recursive procedures can be found on Pages
79-83 of the "Microsoft QuickBASIC 4.0: Programming in BASIC: Selected
Topics" manual for Versions 4.00 and 4.00b, and on Pages 69-72 of the
"Microsoft QuickBASIC 4.5: Programming in BASIC" manual for Version
4.50.

Code Example
------------

The following program can be found in either the "Microsoft QuickBASIC
4.0: BASIC Language Reference" manual on Pages 62-63, or on Pages
50-51 of the ring-bound "Microsoft QuickBASIC 4.5: BASIC Language
Reference" manual for Version 4.50:

DECLARE FUNCTION Reverse$ (StringVar$)
LINE INPUT "Enter string to reverse: ", X$
PRINT Reverse$(X$)
END

FUNCTION Reverse$ (S$)
  C$ = MID$(S$, 1, 1)
  IF C$ = "" THEN
    Reverse$ = ""
  ELSE
    Reverse$ = Reverse$(MID$(S$, 2)) + C$
  END IF
END FUNCTION

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