Is field number valid

Is field number valid ( tablePtr : Pointer ; fieldNum : Integer ) : Boolean
Is field number valid ( tableNum : Integer ; fieldNum : Integer ) : Boolean

Parameter	Type		Description
tableNum	Integer	→	Table number
tablePtr	Pointer	→	Pointer to table
fieldNum	Integer	→	Field number
Function result	Boolean	←	True = field exists in the table False = field does not exist in the table

History

Release	Changes
11 SQL	Created

Description

The Is field number valid command returns True if the field whose number is passed in the fieldNum parameter exists in the table whose number or pointer is passed in the tableNum or tablePtr parameter. If the field does not exist, the command returns False. Keep in mind that the command returns False if the table containing the field is in the Trash of the Explorer.

This command can be used to detect any field deletions, which create gaps in the sequence of field numbers.

Example

It is possible to delete 4D tables and fields. You must take this possibility into account in algorithms used for counting tables and fields. It is necessary to use algorithms combining the Get last table number and Get last field number, as well as Is table number valid and Is field number valid commands. The following is an example of this type of algorithm:

 var $thetable; $thefield : Integer
 For($thetable;1;Get last table number)
    If(Is table number valid($thetable))
       For($thefield;1;Get last field number($thetable))
          If(Is field number valid($thetable;$thefield))
             ... `The field exists and is valid
          End if
       End for
    End if
 End for

See also

Last table number
Is table number valid

Properties

Command number	1000
Thread safe	yes