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It is often desirable to validate that a user entered date is a valid date. There is really no
'out of the box' solution to this.
There are, of course, some ISPF validation methods within ISPF panel
definitions although these
are fairly rudimentary and somewhat error prone, checking mainly for
syntax rather than validity.
ISDATE is our solution to this issue.
ISDATE is a Rexx exec that will, not only check to see if a passed
date is in a correct format, but will also check the validity of
the date. For example: that the number of days in the month is not exceeded.
We have intentionally limited the allowed year to only process years after
1753 the reason for this is explained on our
Zeller's congruence
document. We assume that (unlike Excel) most of the time
the mainframe is used for serious business rather than just for 'fun'.
Thus we see no need to make it support dates before 1753!
So how does ISDATE work and how do you use it?
The format of the call to ISDATE is:
ISDATE(DateToTest,DateFormatToUse)
| DateToTest |
Specifies the string to be checked for a valid date. The string,
unless it is DATE() format, must have the days, months and years
separated by a forward slash (/).
i.e. 12/23/2021
By DATE() Format we mean in Local Date format as specified by Rexx (DD MMM YYYY) i.e 25 JAN 1999 |
| DateFormatToUse |
This is an optional parameter which can be used to change the
default format from MMDDYYYY
The supported values are:
It should be noted also that if the local time format is being used, then DateFormatToUse will be ignored as DDMMYYYY will be used to validate the date. |
Return Codes from ISDATE are:
0 - Date is valid
4 - Help displayed
8 - Date is invalid
12 - Incorrect date format
Sample Calls
|
say "try "date() mydate = date() rc = isdate(mydate) if rc > 0 then do say mydate "is not a valid date" end else do say mydate "is a Valid date" end say "try 01/29/1964" mydate = "01/29/1964" rc = isdate(mydate) if rc > 0 then do say mydale "is not a valid date" end else do say mydate "is a Valid date" end say "try 02/29/2004" rc = isdate("02/29/2004") if rc > 0 then do say "02/29/2004 is not a valid date" end else do say "02/29/2004 is a valid date" end say "try 2000/2/29" rc = isdate("2000/2/29",'yyyymmdd') if rc > 0 then do say "2000/2/29 is not a valid date" end else do say "2000/2/29 is a valid date. Leap year" end say "try 29/2/1900" rc = isdate("29/2/1900",'ddmmyyyy') if rc > 0 then do say "29/2/1900 is not a valid date" end say rc |
Resulting Output
|
try 22 Jan 2022 22 Jan 2022 is a Valid date try 01/29/1964 01/29/1964 is a Valid date try 02/29/2004 02/29/2004 is a valid date try 2000/2/29 2000/2/29 is a valid date. Leap year try 29/2/1900 29/2/1900 is not a valid date 8 |
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