Final answer:
The contents of a pointer to a compound data type in C can be updated by directly assigning new values to the members or by using functions like memcpy() to copy memory. Freeing and reallocating memory is not necessary unless changing the size or type of the pointed data.
Step-by-step explanation:
The contents of a pointer to a compound data type in C can be updated using several methods, including b) Directly assigning new values to the members of the compound data type. This does not require freeing and reallocating memory, as you would simply access the individual elements or members of the structure or union that the pointer is pointing to and assign new values to them. It's similar to how you would access and modify data in an array or a struct when you have a direct reference to it.
Another method could involve using a function like memcpy(), which is useful for copying a block of memory from one location to another. This can be used if you need to update the entire content of a structure with another structure of the same type.
However, the question gives the notion that you might need to 'free and reallocate' memory which is typically not necessary for updating the contents of a compound data structure unless you need to change the size or type of the data the pointer is pointing to.