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The CL Corner: So You're Looking for a Date?

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The CEEDATE and CEELOCT APIs can help!

 

I'm often asked how to determine a date that is some number of days in the future, or in the past, from another date. Doing this type of calculation yourself can be error-prone in terms of adjusting for the number of days in a month or the number of days in a leap year, getting the right calculation for a leap year, etc. Fortunately, i5/OS provides the ILE Common Execution Environment (CEE) Date and Time APIs to greatly simplify this type of calculation (they're documented in the i5/OS Information Center here). An introduction to the various CEE APIs (there are more than just date and time APIs) can be found here.

 

One starting date that comes up frequently is the current date and time. The Get Current Local Time API CEELOCT returns the local time. The API documentation can be found here, and I've repeated the API's parameter list below:

 

Required Parameters:

1

output_Lilian

Output

INT4

2

output_seconds

Output

FLOAT8

3

output_Gregorian

Output

CHAR23


  Omissible Parameter:

4

fc

Output

FEEDBACK

 

The CEELOCT API has three required parameters and one omissible parameter. The first parameter, output_Lilian, is a 4-byte signed integer (for CL, this would be TYPE(*INT)) that represents the current local date in Lilian format. In a Lilian-formatted date, a value of 1 represents October 15, 1582; a value of 2 represents October 16, 1582; and so on. Using this sequential numbering scheme, if today is March 21, 2008, then the Lilian date would be 155387. Finding a date 60 days in the future is then done by simply adding 60 to 155387, giving us 155447. And as you might expect, there is another API, Convert Lilian Date to Character Format (or CEEDATE), that will take a Lilian date such as our calculated 155447 and then return the date in formats such as 5/20/2008, 05/20/2008, or even Tuesday, 20 May 2008. Likewise, finding the difference between two dates, in days, is as simple as subtracting one date from the other. It just doesn't get much easier than this!

 

We won't be using the other three parameters in the following review of the CEE date and time APIs, but in case you're wondering...

•·                     Output_seconds is an 8-byte floating point value that represents the number of seconds since 00:00:00 October 14, 1582. As CL doesn't directly support floating point variables, this would be defined as TYPE(*CHAR) with LEN(8).

•·                     output_Gregorian is a 23-byte character string with the date formatted as YYYYMMDD in the first eight bytes. Refer to the API documentation for how the rest of this parameter is formatted.

•·                     fc is a 12-byte error-feedback structure that is omissible, meaning that you must use the fourth parameter, but you can pass the special value *OMIT rather than an actual value. We will be using *OMIT, which tells the API to return errors as messages that we can monitor for with MONMSG.

 

And if you happen to be the curious type, October 15, 1582, is designated day 1 due to October 14, 1582, being a day that doesn't exist in the Gregorian calendar (the Gregorian day October 15, 1582, was preceded by the Julian day October 4[VM1] , 1582)! Lilian dating is named after Aloysius Lilius, who devised the calendaring system implemented by Pope Gregory XIII in 1582.

 

The Convert Lilian Date to Character Format (CEEDATE) API can be found here, and the parameter descriptions are provided below:

 

Required Parameters:

1

input_Lilian_date

Input

INT4

2

picture_string

Input

VSTRING

3

output_char_date

Output

VSTRING


  Omissible Parameter:

4

fc

Output

FEEDBACK

 

The CEEDATE API has three required parameters and one omissible parameter. The first parameter, input_Lilian_date, is the Lilian date value we want to convert to a character string. Following our earlier example, this would be the value 155447, representing the date 60 days from March 21, 2008. The second parameter, picture_string, is a variable-length character string describing how we want the returned date to be formatted. Formatting options include values such as 'YY' and 'YYYY' to represent 2- and 4-digit years, respectively; 'MM' and 'ZM' for 2-digit month and zero-suppressed month values; 'W', 'Www', and 'Wwwwwwww' for day of week values such as M, Mon, and Monday; etc. The third parameter, output_char_date, is a variable-length character parameter used to return the formatted date. The fourth parameter, fc, is the common error-feedback structure used by CEE APIs.

 

With this introduction, the following program, CURADD60, demonstrates how to retrieve the current date in Lilian format, add 60 days to the current day, convert the result to a 'Day of week, Day Month Year' format, and then display the formatted result.

 

 

         Pgm                                                      

    Dcl        Var(&CurLilDate) Type(*Int)                   

    Dcl        Var(&NewLilDate) Type(*Int)                   

    Dcl        Var(&CurLilTime) Type(*Char) Len(8)           

    Dcl        Var(&CurGregDt)  Type(*Char) Len(23)          

    Dcl        Var(&NewGregDt)  Type(*Char) Len(32)          

                                                             

    CallPrc    Prc(CEELOCT) Parm((&CurLilDate) (&CurLilTime) +

                 (&CurGregDt) (*Omit))                       

                                                             

    ChgVar     Var(&NewLilDate) Value(&CurLilDate + 60)      

                                                             

    CallPrc    Prc(CEEDATE) Parm((&NewLilDate) +             

                 ('Wwwwwwwwwz, DD Mmm YYYY') (&NewGregDt) +  

                 (*Omit))                                    

                                                             

    SndPgmMsg  Msg(&NewGregDt) ToPgmQ(*Ext)                  

    EndPgm 

 

Running CURADD60, if the current date is March 21, 2008, you should see the following message being displayed:

 

 

 Tuesday, 20 May 2008

 

It's that easy to determine a date x days from a starting date! In the next article, we'll look at other CEE date and time APIs, in particular Convert Date to Lilian Format (CEEDAYS) to convert arbitrary dates in various formats to Lilian dates and Calculate Day of Week from Lilian Date (CEEDYWK) to determine if a future date happens to fall on a Saturday or Sunday. If it does, we'll use the date for the following Monday. As Monday may very well be a holiday, we'll also look in a subsequent column at one approach (there are many) to avoid generating dates that fall on holidays in addition to weekends.

More CL Questions?              

Wondering how to accomplish a function in CL? Send your CL-related questions to me at This email address is being protected from spambots. You need JavaScript enabled to view it.. I'll try to answer your burning questions in future columns.

Bruce Vining

Bruce Vining is president and co-founder of Bruce Vining Services, LLC, a firm providing contract programming and consulting services to the System i community. He began his career in 1979 as an IBM Systems Engineer in St. Louis, Missouri, and then transferred to Rochester, Minnesota, in 1985, where he continues to reside. From 1992 until leaving IBM in 2007, Bruce was a member of the System Design Control Group responsible for OS/400 and i5/OS areas such as System APIs, Globalization, and Software Serviceability. He is also the designer of Control Language for Files (CLF).A frequent speaker and writer, Bruce can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it.. 


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