How do you handle date and time operations in RPGLE?

Handling dates and times in RPGLE involves using specific data types, built-in functions (BIFs), and understanding the various formats available. Here's a comprehensive overview:

1. Date and Time Data Types:

Date: D data type. Stores a date in a specific format (e.g., YYYY-MM-DD, MM/DD/YY).
Time: T data type. Stores a time in a specific format (e.g., HH.MM.SS, HH:MM:SS).
Timestamp: Z data type. Stores both date and time.

2. Defining Date/Time Variables :

DCL-S  MyDate       D   INZ(2024-03-15);  // Initialized to March 15, 2024
DCL-S  MyTime       T   INZ(14.30.00);  // Initialized to 2:30 PM
DCL-S  MyTimestamp  Z   INZ(2024-03-15-14.30.00); // Date and Time

3. Date/Time Formats:

System-defined formats: The default format is usually *ISO (YYYY-MM-DD) for dates and *HMS (HH.MM.SS) for times, but this can be changed using system values.
User-defined formats: You can specify the format when defining date/time variables or using BIFs. Common formats include:
- Dates: *MDY (MM/DD/YY), *DMY (DD/MM/YY), *YMD (YYYYMMDD), *JUL (Julian), etc.
- Times: *HMS (HH.MM.SS), *ISO (HH:MM:SS), etc.
Format codes: You use format codes within BIFs to convert between different date/time formats. Examples: %date(*YMD) converts a date to YYYYMMDD format.

4. Built-in Functions (BIFs):

%DATE: Converts a character or numeric value to a date.
%TIME: Converts a character or numeric value to a time.
%TIMESTAMP: Converts a character or numeric value to a timestamp.
%CHAR: Converts a date, time, or timestamp to a character value. Crucial for displaying or using date/time values in character strings.
%DAYS, %MONTHS, %YEARS: Adds or subtracts days, months, or years from a date.
%DIFF: Calculates the difference between two dates or times.
%SUBDT: Extracts a portion of a date or time (e.g., the month from a date).
%SCAN: Searches for date/time components within a string.

5. Date/Time Arithmetic:

You can perform arithmetic operations on dates and times :

MyDate = MyDate + %DAYS(7);   // Add 7 days
MyDate = MyDate - %MONTHS(1); // Subtract 1 month
MyTimestamp = MyTimestamp + %MINUTES(30); // Add 30 minutes

6. Converting Between Formats :

// Convert date to character in a specific format
MyCharDate = %CHAR(MyDate : *MDY); // MyCharDate will be in MM/DD/YY format

// Convert character to date
MyDate = %DATE('12/25/2024' : *MDY);

// Get the current date in YYYYMMDD format
CurrentDate = %CHAR(%DATE() : *YMD);

7. Working with Timestamps :

Timestamps are particularly useful for tracking events and recording when something occurred.

// Get the current timestamp
Now = %TIMESTAMP();

8. Handling Date/Time Errors:

Data type mismatch: If you try to move a value of the wrong data type into a date/time field, you'll get an error.
Invalid date/time values: Make sure the date/time values you're working with are valid (e.g., no February 30th).
Format errors: When converting between character and date/time values, ensure the formats match.

Example :

DCL-S  OrderDate      D   INZ(2024-03-01);
DCL-S  ShipDate       D;
DCL-S  DaysToShip     INT(10);
DCL-C  DueDate        D   INZ(2024-12-31); // Example Due Date

ShipDate = OrderDate + %DAYS(10);  // 10 days after order

DaysToShip = %DIFF(ShipDate : OrderDate : *D); // Calculate days between dates

IF ShipDate > DueDate;
  DSPLY ('Order is late!');
ENDIF;

DSPLY ('Order Date: ' + %CHAR(OrderDate : *MDY));
DSPLY ('Ship Date: ' + %CHAR(ShipDate : *MDY));

By understanding these concepts and using the appropriate BIFs, you can effectively handle date and time operations in your RPGLE programs. Remember to pay close attention to data types and formats to avoid errors.