Defining Parameter Data

General syntax of DEFINE DATA PARAMETER:

DEFINE DATA
   PARAMETER

USING parameter-data-area

parameter-data-definition ../graphics/dot3.gif
END-DEFINE

This document covers the following topics:

For explanations 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, function or dialog. 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

../graphics/cbo5.gif

 (format-length[/array-definition])

../graphics/cbc5.gif

 [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:

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 Studio.

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.

The handle definition in the DEFINE DATA statement is generated automatically on the creation of a dialog element or dialog.

After having defined a handle, you can use the handle name in any statement to query, set or modify attribute values for the defined dialog-element-type.

Examples:

1 #SAVEAS-MENUITEM HANDLE OF MENUITEM
1 #OK-BUTTON (1:10) HANDLE OF PUSHBUTTON

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.

For parameter definitions for dialogs, the following applies:

  • Without BY VALUE, a parameter, as specified in the inline definition of a dialog's parameter data area, is transferred via its address (by reference); the format and length of the parameter in an OPEN DIALOG or SEND EVENT statement, for example, must match the format and length of the parameter in the inline parameter data definition of the dialog. You can use a parameter by reference in the before open and after open event handlers and in all other events if the used parameters are transferred in the SEND EVENT statement triggering this event.

  • With BY VALUE, a parameter is transferred via its value; format and length do not have to match; the parameter in the OPEN DIALOG or SEND EVENT statement must be data transfer compatible with the parameter of the dialog.

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.

Note:
BY VALUE RESULT cannot be used in dialogs.

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.