8.7. Union

A union construct is very similar to a struct construct. Like a struct, the union declaration specifies data types and variable names of a new data structure, of sorts. Like with the 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 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;