When you need to add an interval while allowing larger calendar fields to change, it helps to understand both the normal result and what changes with different inputs. This guide focuses on practical examples rather than repeating PHP background material.
IntlCalendar::add provides the behavior described below. IntlCalendar represents a locale-aware ICU calendar. Month indexes are zero-based, while epoch time uses milliseconds.
What Is IntlCalendar::add in PHP?
Add an interval while allowing larger calendar fields to change. IntlCalendar represents a locale-aware ICU calendar. Month indexes are zero-based, while epoch time uses milliseconds.
Its syntax is:
$calendar->add(...)
Parameters and return value: Read the argument names and optional values in the signature above. Methods use an existing object, while stand-alone functions take direct arguments. The examples demonstrate the relevant arguments and the value returned or the object modified.
Important: Unlike roll(), add() may update larger calendar fields.
Example 1: Basic Usage
This first example demonstrates how to add an interval while allowing larger calendar fields to change with a small input.
<?php
$calendar = IntlCalendar::createInstance("UTC", "en_US");
$calendar->add(IntlCalendar::FIELD_DAY_OF_MONTH, 10);
echo $calendar->get(IntlCalendar::FIELD_DAY_OF_MONTH);
The example uses the simplest useful form. IntlCalendar represents a locale-aware ICU calendar. Month indexes are zero-based, while epoch time uses milliseconds. The output may depend on the active ICU locale, PHP configuration, or input supplied to the function.
Example 2: Another Case
Here the input or option changes, making it easier to see where the behavior differs. Unlike roll(), add() may update larger calendar fields.
<?php
$calendar = IntlCalendar::createInstance("UTC", "en_US");
$calendar->add(IntlCalendar::FIELD_MONTH, 1);
echo $calendar->get(IntlCalendar::FIELD_MONTH);
Compare the result to the first example. DateTimeImmutable is often simpler for Gregorian dates; IntlCalendar is useful for ICU calendar systems.
Practical Example: Applying the Function
This standalone example shows how the same operation fits into a small application task. The intl extension is required for this example.
<?php
$calendar = IntlCalendar::createInstance("UTC", "en_US");
$calendar->set(2026, 0, 30);
$calendar->add(IntlCalendar::FIELD_MONTH, 1);
echo $calendar->get(IntlCalendar::FIELD_DAY_OF_MONTH);
The example keeps the operation visible and gives you a starting point for using it in an application. Unlike roll(), add() may update larger calendar fields.
Important Behavior and Edge Cases
- Core behavior: IntlCalendar represents a locale-aware ICU calendar. Month indexes are zero-based, while epoch time uses milliseconds.
- Return value: Check the result separately from changes to passed-in arrays, iterators, or object state.
- Data constraints: Unlike roll(), add() may update larger calendar fields.
- Environment: The intl extension is required for this example.
Comparison With Related Functions
| Function or Approach | When to Use It |
|---|---|
IntlCalendar::add | Add an interval while allowing larger calendar fields to change. |
| Related PHP APIs | DateTimeImmutable is often simpler for Gregorian dates; IntlCalendar is useful for ICU calendar systems. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Assuming the function works on every kind of input | Follow the declared argument types and check the input format before calling it. |
| Ignoring the behavior of the result | Unlike roll(), add() may update larger calendar fields. |
| Using the wrong related PHP API | DateTimeImmutable is often simpler for Gregorian dates; IntlCalendar is useful for ICU calendar systems. |
Key Takeaways
IntlCalendar::addhelps you add an interval while allowing larger calendar fields to change.- IntlCalendar represents a locale-aware ICU calendar. Month indexes are zero-based, while epoch time uses milliseconds.
- Unlike roll(), add() may update larger calendar fields.
- DateTimeImmutable is often simpler for Gregorian dates; IntlCalendar is useful for ICU calendar systems.
IntlCalendar::add is useful when you need to add an interval while allowing larger calendar fields to change. Start with the small examples, then adapt the practical example while respecting its input and environment requirements.