Unions, Bit-Fields & Dynamic Memory Management

Unions:

- In a union, all members share the EXACT SAME starting memory address.

- Size of union = size of its largest member (padded to alignment requirement).

- Used for memory conservation and type punning (e.g. testing endianness).

Bit-Fields:

- Allow variables of specified bit widths inside structures (e.g. unsigned int flag : 1;).

- Multiple bit-fields pack into a single machine word.

- malloc(size): Allocates size uninitialized bytes on Heap. Returns void* (or NULL on failure).

- calloc(n, size): Allocates and initializes all bytes to ZERO.

- realloc(ptr, new_size): Resizes existing block, potentially moving it to a new heap address.

- free(ptr): Returns memory to heap. Does NOT set pointer to NULL, creating a dangling pointer!