Unions
Unions
Unions are similar to structures, but a union’s members all share the same memory location. In essence, a union is a variable that is capable of holding different types of data at different times.

Unions:

  • May contain any number of members
  • Members may be of any data type
  • Are as large as their largest member
  • Use exactly the same syntax as structures except struct is replaced with union

Creating an Union

Syntax

union unionName
{
type1 memberName1;

typen memberNamen;
}

Example

Purpose of a Union

Unions are similar to structures except that struct by itself outside of a union assigns a new memory location upon declaration.

union allows the same memory location to be viewed and manipulated as different data types.

Example

Creating a Union with typedef

Syntax

typedef union unionTagoptional
{
type1 memberName1;

typen memberNamen;
} typeName;

Example

Unions Memory Storage

Union variables may be declared exactly like structure variables. Memory is allocated to accommodate the union's largest member.

Examples

Unions.png
Unions2.png
Unions3.png
Unions4.png

Example from typical .h file

UnionsFinal.png
© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.