| Navigation: Language Reference > 5 - Declaration Attributes > Variable and Entity Attributes >====== PRE (set label prefix) ====== |    |
PRE( [ prefix ] )
| PRE | Provides a label prefix for complex data structures. |
| prefix | Acceptable characters are alphabet letters, numerals 0 through 9, and the underscore character. A prefix must start with an alpha character or underscore. By convention, a prefix is 1-3 characters, although it can be longer. |
The PRE attribute provides a label prefix for a FILE, QUEUE, GROUP, REPORT, or ITEMIZE structure. PRE is also valid on a LIKE declaration to provide a separate prefix when LIKE is used to declare another copy of a complex data structure.
PRE is used to distinguish between identical variable names that occur in different structures. When a data element from a complex data structure is referenced in executable statements, assignments, and parameter lists, the prefix is attached to its label by a colon (Pre:Label).
PRE is essentially a legacy attribute which is being replaced by a more flexible method to distinguish between identical variable names that occur in different structures: Field Qualification syntax. When referenced in executable statements, assignments, and parameter lists, the label of the structure containing the field is attached to the field label by a period (GroupName.Label).
The use of PRE with TYPE in a FILE structure is not supported.
Example:
MasterFile FILE,DRIVER('Clarion'),PRE(Mst) !Declare master file layout
Record RECORD
AcctNumber LONG !Referenced as Mst:AcctNumber or MasterFile.AcctNumber
END
END
Detail FILE,DRIVER('Clarion'),PRE(Dtl) !Declare detail file layout
Record RECORD
AcctNumber LONG !Referenced as Dtl:AcctNumber or Detail.AcctNumber
END
END
SaveQueue QUEUE,PRE(Sav)
AcctNumber LONG !Referenced as Sav:AcctNumber or SaveQueue.AcctNumber
END
G1 GROUP,PRE(Mem) !Declare some memory variables
Message STRING(30) !with the Mem prefix
END
G2 LIKE(G1),PRE(Me2) !Another GROUP LIKE the first containing same
CODE !variables using the “Me2” prefix
IF Dtl:AcctNumber <;> Mst:AcctNumber !Is it a new account
Mem:Message = 'New Account' !display message
Me2:Message = 'Variable in LIKE group'
END
IF Detail.AcctNumber <;> Masterfile.AcctNumber !Same expression
G1.Message = 'New Account' ! display message
G2.Message = 'Same Variable in LIKE group'
END
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