Q34279: Cannot Pass More Than 21 Dynamic Array Elements to Subprogram

Article: Q34279
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 16-DEC-1989

Passing more than 20 individual elements of a dynamic array to a
subprogram or function procedure will produce the compiler error "Too
many arguments in function call." This limitation occurs for all types
of dynamic arrays. Either the whole array should be passed, or each
item should be copied to a temporary variable and then passed to the
subprogram or function.

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

This limitation occurs because of special handling done for dynamic
arrays. When a subprogram is called, there is no way of ensuring that
the dynamic array will not move. Therefore, when individual array
elements are passed by reference, each is copied into a temporary
location. These temporary locations are passed to the routine and then
reassigned to the array when the routine is exited. There is a limit
of 20 temporary locations.

The following is a complete code example:

DECLARE SUB test2 (a1!, a2!, a3!, a4!, a5!, a6!, a7!, a8!, a9!,_
                   a10!, a11!, a12!, a13!, a14!, a15!, a16!, a17!,_
                   a18!, a19!, a20!, a21!)
x = 30
DIM a(x)
CALL test2(a(1), a(2), a(3), a(4), a(5), a(6), a(7), a(8), a(9),_
           a(10), a(11), a(12), a(13), a(14), a(15), a(16), a(17),_
           a(18), a(19), a(20), a(21))
END

SUB test2 (a1!, a2!, a3!, a4!, a5!, a6!, a7!, a8!, a9!, a10!, a11!,_
           a12!, a13!, a14!, a15!, a16!, a17!, a18!, a19!, a20!, a21!)

    PRINT "hello"

END SUB

The following is the compiler output:

Microsoft (R) QuickBASIC Compiler Version 4.00b
Copyright (C) Microsoft Corp. 1982-1988. All rights reserved.
 0053   0006  ...a(18),a(19),a(20),a(21))
                                   ^ Too many arguments in function call

43059 Bytes Available
37660 Bytes Free

    0 Warning Error(s)
    1 Severe  Error(s)

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