Defining Parameter Data

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# Defining Parameter Data

General syntax of `DEFINE DATA PARAMETER`:

`DEFINE DATA`
`PARAMETER` |  | `USING` parameter-data-area |
parameter-data-definition
`END-DEFINE`

This document covers the following topics:

- Function

- Restrictions

- Syntax Description

For an explanation of the symbols used in the syntax diagram, see Syntax Symbols.

## Function

The `DEFINE DATA PARAMETER` statement is used to define the data elements that are to be used as incoming parameters in a Natural subprogram, external subroutine, helproutine or function. These parameters can be defined within the statement itself (see Parameter Data Definition); or they can be defined outside the program in a parameter data area (PDA), with the statement referencing that data area.

## Restrictions

- Parameter data elements must not be assigned initial or constant values, and they must not have edit mask (`EM`), header (`HD`) or print mode (`PM`) definitions; see also EM, HD, PM Parameters for Field/Variable.

- The parameter data area and the objects which reference it must be contained in the same library (or in a steplib).

## Syntax Description

Syntax Element | Description
--- | ---
`USING` `parameter-data-area` | Parameter Data Area (PDA) Name: The name of the `parameter-data-area` (PDA) that contains data elements which are used as parameters in a subprogram, external subroutine or dialog.
`parameter-data-definition` | Parameter Data Definition: Instead of using a PDA, you can define parameter data directly. See Parameter Data Definition.
`END-DEFINE` | End of DEFINE DATA Statement: The Natural reserved word `END-DEFINE` must be used to end the `DEFINE DATA` statement.

### Parameter Data Definition

For parameter data definition, the following syntax applies:

| level |  | group-name [(array-definition)] |  |
redefinition
variable-name |  | (format-length[/array-definition]) |  | [`BY VALUE` [`RESULT`]] [`OPTIONAL`]
( |  | `A` `U` `B` |  | [/array-definition]) |  | `DYNAMIC`
[(array-definition)] `HANDLE OF OBJECT`

Syntax Element Description:

Syntax Element | Description
--- | ---
`level` | Level Number: Level number is a 1- or 2-digit number in the range from 01 to 99 (the leading zero is optional) used in conjunction with field grouping. Fields assigned a level number of 02 or greater are considered to be a part of the immediately preceding group which has been assigned a lower level number. The definition of a group enables reference to a series of fields (may also be only 1 field) by using the group name. With certain statements (`CALL`, `CALLNAT`, `RESET`, `WRITE`, etc.), you may specify the group name as a shortcut to reference the fields contained in the group. A group may consist of other groups. When assigning the level numbers for a group, no level numbers may be skipped.
`group-name` | Group Name: The name of a group. The name must adhere to the rules for defining a Natural variable name. See also the following sections: Naming Conventions for User-Defined Variables in Using Natural. Qualifying Data Structures in the Programming Guide.
`array-definition` | Array Dimension Definition: With an array-definition, you define the lower and upper bounds of dimensions in an array-definition. For further information, see Array Dimension Definition and Variable Arrays in a Parameter Data Area.
`redefinition` | Redefinition: A `redefinition` may be used to redefine a group or a single field/variable (that is a scalar or an array). See Redefinition. Note In a `parameter-data-definition`, a redefinition of groups is only permitted within a `REDEFINE` block.
`variable-name` | Variable Name: The name to be assigned to the variable. Rules for Natural variable names apply. For information on naming conventions for user-defined variables. For further information, see Naming Conventions for User-Defined Variables in Using Natural.
`format-length` | Format/Length Definition: The format and length of the field. For information on format/length definition of user-defined variables, see Format and Length of User-Defined Variables in the Programming Guide.
`HANDLE OF OBJECT` | Handle of Object: Used in conjunction with NaturalX. A handle identifies a dialog element in code and is stored in handle variables. For further information, see NaturalX in the Programming Guide.
`A`, `U` or `B` | Data Type: Alphanumeric (`A`), Unicode (`U`) or binary (`B`) for dynamic variable.
`DYNAMIC` | DYNAMIC Option: A parameter may be defined as `DYNAMIC`. For further information on processing dynamic variables, see Introduction to Dynamic Variables and Fields in the Programming Guide.
| Call Mode: Depending on whether call-by-reference, call-by-value or call-by-value-result is used, the appropriate transfer mechanism is applicable. For further information, see the `CALLNAT` statement.
(without `BY VALUE`) | Call-by-Reference: Call-by-reference is active by default when you omit the `BY VALUE` keywords. In this case, a parameter is passed to a subprogram/subroutine/function by reference (that is, via its address); therefore a field specified as parameter in a `CALLNAT`/`PERFORM` statement must have the same format/length as the corresponding field in the invoked subprogram/subroutine/function.
`BY VALUE` | Call-by-Value: When you specify `BY VALUE`, a parameter is passed to a subprogram/subroutine/function by value; that is, the actual parameter value (instead of its address) is passed. Consequently, the field in the subprogram/subroutine/function need not have the same format/length as the parameter passed in the `CALLNAT`/`PERFORM` statement or in the function call. The formats/lengths must only be data transfer compatible. For data transfer compatibility, the Rules for Arithmetic Assignment and Data Transfer apply (see Programming Guide). `BY VALUE` allows you, for example, to increase the length of a field in a subprogram/subroutine/function (if this should become necessary due to an enhancement of the subprogram/subroutine) without having to adjust any of the objects that invoke the subprogram/subroutine/function.
Example of `BY VALUE`:
    * Program
    DEFINE DATA LOCAL
    1 #FIELDA (P5)
    ...
    END-DEFINE
    ...
    CALLNAT 'SUBR01' #FIELDA...
    * Subroutine SUBR01
    DEFINE DATA PARAMETER
    1 #FIELDB (P9) BY VALUE
    END-DEFINE
    ...
`BY VALUE RESULT` | Call-by-Value-Result: While `BY VALUE` applies to a parameter passed to a subprogram/subroutine/function, `BY VALUE RESULT` causes the parameter to be passed by value in both directions; that is, the actual parameter value is passed from the invoking object to the subprogram/subroutine/function and, on return to the invoking object, the actual parameter value is passed from the subprogram/subroutine/function back to the invoking object. With `BY VALUE RESULT`, the formats/lengths of the fields concerned must be data transfer compatible in both directions.
`OPTIONAL` | Optional Parameters: For a parameter defined without `OPTIONAL` (default), a value must be passed from the invoking object. For a parameter defined with `OPTIONAL`, a value can, but need not be passed from the invoking object to this parameter. In the invoking object, the notation `nX` is used to indicate parameters which are skipped, that is, for which no values are passed. With the `SPECIFIED` option you can find out at run time whether an optional parameter has been defined or not.