.. _unions:
.. _union:

Union
======

A :keyword:`union` construct is very similar to a :keyword:`struct`
construct. Like a :keyword:`struct`, the :keyword:`union` declaration
specifies data types and variable names of a new data structure, of sorts.
Like with the :keyword:`struct`, the allocation of the memory comes not when
you define the union, but when you declare a variable of that type.
Accessing an item from a union uses the same syntax as accessing an item in
a struct.  The difference is that a :keyword:`union` shares the same storage
area for all the elements rather than allocating a separate storage location
for each. Thus, a union actually only stores one element. It is the
programmers responsibility to keep track of what member name is being used
with a particular variable.

::

    union size {
        int pounds;
        float tons;
    };
    
    union size bike, tank;
    
    bike.pounds = 19;
    tank.tons = 60.3;