POS - Field Identification Function

Format/length: I4

The system function POS(field-name) returns an identification of the field whose name is specified with the system function. The value returned is an internal representation of the field address.

POS(field-name) may be used to identify a specific field, regardless of its position in a map. This means that the sequence and number of fields in a map may be changed, but POS(field-name) will still uniquely identify the same field. With this, for example, you need only a single REINPUT statement to make the field to be MARKed dependent on the program logic.

Example: 

DECIDE ON FIRST VALUE OF ... 
   VALUE ... 
      COMPUTE #FIELDX = POS(FIELD1) 
   VALUE ... 
      COMPUTE #FIELDX = POS(FIELD2) 
   ... 
END-DECIDE 
... 
REINPUT ... MARK #FIELDX

If the field specified with POS is an array, a specific occurrence must be specified; for example, POS(FIELDX(5)). POS cannot be applied to an array range.

Note:
POS cannot distinguish between two different variables that start at the same storage position (REDEFINE variables) since the internal field address returned by POS is the same for both.

POS and *CURS-FIELD

The system function POS(field-name) may be used in conjunction with the Natural system variable *CURS-FIELD to make the execution of certain functions dependent on which field the cursor is currently positioned in.

*CURS-FIELD contains the internal identification of the field in which the cursor is currently positioned; it cannot be used by itself, but only in conjunction with POS(field-name). You may use them to check if the cursor is currently positioned in a specific field and have processing performed depending on that condition.

Example: 

IF *CURS-FIELD = POS(FIELDX) 
   MOVE *CURS-FIELD TO #FIELDY 
END-IF 
... 
REINPUT ... MARK #FIELDY

Notes:

  1. The values of *CURS-FIELD and POS(field-name) serve only as internal identifications of the fields and cannot be used for arithmetic operations.
  2. The value returned by POS(field-name) for an occurrence of an X-array (an array for which at least one bound in at least one dimension is specified as expansible) may change after the number of occurrences for a dimension of the array has been changed using the EXPAND, RESIZE or REDUCE statements.
  3. Natural RPC: If *CURS-FIELD and POS(field-name) refer to a context variable, the resulting information can only be used within the same conversation.
  4. In Natural for Ajax applications, *CURS-FIELD identifies the operand that represents the value of the control that has the input focus. You may use *CURS-FIELD in conjunction with the POS function to check for the control that has the input focus and perform processing depending on that condition.
  5. *CURS-FIELD and POS(field-name) cannot distinguish between two different variables that start at the same storage position (REDEFINE variables) since the internal field addresses returned by *CURS-FIELD and POS(field-name) are the same for both variables.

See also Dialog Design, Field Sensitive Processing and Simplifying Programming in the Programming Guide.