Q41535: Syntax Differs When Calling a SUB without the CALL Keyword

Article: Q41535
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 14-DEC-1989

When calling a SUBprogram in QuickBASIC without the keyword "CALL" (by
specifying just the SUB name and arguments), you must omit the
parentheses around the parameter list. This is known as an "implied
CALL" statement. You must also declare that procedure in a DECLARE
statement.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
and 4.50, Microsoft BASIC Compiler Versions 6.00 and 6.00b, and
Microsoft BASIC PDS Version 7.00. Earlier versions of these products
do not support the implied CALL syntax.

The normal form of the CALL statement is as follows:

   CALL foo (arg1,arg2)

In the above example, arg1 and arg2 are passed "by reference." Passing
"by reference" means that if the subprogram changes the values of the
passed parameters, they are passed back changed.

If an individual parameter is placed inside parentheses, the parameter
is passed "by value":

   CALL foo ((arg1),(arg2))

Passing a variable "by value" means that only its value is passed, and
the value of the variable in the calling program is not changed by
assignments in the SUBprogram.

If the CALL statement is omitted from the line (i.e., only the SUB
name is given to indicate the CALL), then the outermost parentheses
must be omitted.

The proper syntax for a call by reference without the CALL keyword is
as follows:

   foo arg1,arg2

The proper syntax for a call by value without the CALL keyword is as
follows:

   foo (arg1),(arg2)

The following is an example of the difference between calling by
reference and by value:

  DECLARE SUB foo (arg1, arg2)
  arg1 = 5
  arg2 = 6
  foo arg1, arg2                        ;call by reference
  PRINT arg1, arg2                      ;results in 1 and 2
  arg1 = 5
  foo (arg1), (arg2)          ;call by value
  PRINT arg1, arg2                      ;results in 5 and 6
  END

  SUB foo (arg1, arg2)
    arg1 = 1
    arg2 = 2
  END SUB

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.