Improper Access to a Union
ANSI 220.127.116.11 A member of a union object is accessed using a member of a different type
If a union of two types is declared and one value is stored, but the union is accessed with the other type, the results are unreliable.
For example, a union of float and int is declared. A float value is stored, but the program later accesses the value as an int. In such a situation, the value would depend on the internal storage of float values. The integer value would not be reliable.