---
title: Undefined Components
framework: foundation
role: collectionGroup
role_heading: API Collection
path: foundation/1430344-undefined-components
---

# Undefined Components

Constants that denote that the value of a date component is undefined.

## Overview

Overview For example, when an NSDateComponents object is created as the result of calculating the distance in time between two dates represented by a particular calendar, the value for the weekOfYear component would be set to NSDateComponentUndefined.

## Topics

### Constants

- [NSDateComponentUndefined](foundation/nsdatecomponentundefined.md)
- [NSUndefinedDateComponent](foundation/nsundefineddatecomponent.md)

## See Also

### Validating a Date

- [isValidDate](foundation/nsdatecomponents/isvaliddate.md)
- [isValidDate(in:)](foundation/nsdatecomponents/isvaliddate(in:).md)
- [date](foundation/nsdatecomponents/date.md)