Question on Unions in C

So, I know that a pointer is a variable that stores a memory address (basic 4 or 8 bytes). If I place a pointer in a Union type, does the memory address stored by the pointer share the same memory space as the other types, or does the data at the memory address share the same memory?

Or, in other words, if I union a double and a char*, will I memory leak/segfault if I assign the double to anything?

>>14
This is a silly way of achieving polymorphism, the effort to maintain the code doesn't scale when the number of types becomes very large.

Unions are useful since the implementation specified behavior for them is very often sane and useful.