What is the use of union?

Advertisements. A union is a special data type available in C that allows to store different data types in the same memory location . You can define a union with many members, but only one member can contain a value at any given time.

The UNION operator is used to combine the result-set of two or more SELECT statements . Every SELECT statement within UNION must have the same number of columns. The columns must also have similar data types. The columns in every SELECT statement must also be in the same order.

The primary use of a union is allowing access to a common location by different data types , for example hardware input/output access, bitfield and word sharing, or type punning. Unions can also provide low-level polymorphism.