Unions
Union types are special structures which allow access to the same memory using different type descriptions; one could, for example, describe a union of data types which would allow reading the same data as an integer, a float or a user declared type:
union { int i; float f; struct { unsigned int u; double d; } s; } u;In the above example the total size of u is the size of u.s (which is the sum of the sizes of u.s.u and u.s.d), since s is larger than both i and f. When assigning something to u.i, some parts of u.f may be preserved if u.i is smaller than u.f.
Reading from a union member is not the same as casting since the value of the member is not converted, but merely read.
Read more about this topic: C Data Types
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