Overriding the Default Date Window Using the DATTIM PROCESS Statement Option

Sometimes you may not be able to avoid moving dates between 4-digit and 2-digit years, and you know that inaccuracy will result based on the default windowing algorithm that ILE COBOL uses. You can use the DATTIM process statement option to change the default date window.

The syntax of the DATTIM process statement is:

Syntax

Read syntax diagramSkip visual syntax diagramDATTIM(4-digit base century2-digit base year)
4-digit base century
This must be the first argument. Defines the base century that ILE COBOL uses for its windowing algorithm. If the DATTIM process statement option is not specified, 1900 is used.

The 4-digit-base-century also affects the interpretation of the @C conversion specifier. The @C conversion specifier represents a 1-digit century, whose value ranges between 0 and 9. A 0 for a 1-digit century represents a base century of 1900, 1 = 2000, … 9 = 2800. So, a date data item whose format is @C/%y/%m and whose value is 1/12/05, represents year 2012, the first day of month 5 (May). However, 0 of @C is really equal to the 4-digit base century. Thus, a DATTIM(2200, 40) would cause 0 = 2200, 1 = 2300 …, 9 = 3100.

2-digit base year
This must be the second argument. Defines the base year that ILE COBOL uses for its windowing algorithm. If the DATTIM process statement option is not specified, 40 is used.
The default DATTIM(1900, 40) results in a 100-year window of 1940 through 2039. To solve the problem encountered in our previous example, we could set the DATTIM option in either of the following ways:
  • Specifying DATTIM(1900 70) would result in a 100-year window of 1970 through 2069
  • If we assume that all 2-digit years are in the 21st century we could specify DATTIM(2000 00), which would result in a 100-year window of 2000 through 2099.
Given either of these options on a PROCESS statement in the previous example, the output would be: 
 date2 =2039/07/12
 date3 =39/07/12
 date2 =2040/07/12

The only change in the output is the result of move  3 . If you remember from the previous example, the output was date2 =1940/07/12, which was an inaccurate result from moving an updated 2-digit date to a 4-digit date based on the default ILE COBOL windowing algorithm (base century of 1900 and base year of 40).