A strong answer
A strong candidate frames When should a function take a pointer instead of a reference? around the exact memory layout, compiler semantics, and hardware execution model covered in Pointers Versus References, and nullptr. Compare rebinding, null state, and assignment for references versus pointers.
C++ has two ways to refer to an object that lives elsewhere: a reference, from lesson 7 of module 2, and a pointer, from lesson 6 of this module. Underneath, both hold an address. So when do you use which?
A concrete problem shows the difference. A function searches a vector for a negative number. It should hand back the element so that the caller can change it, but sometimes there is no such element. A reference cannot say "nothing", because it must always refer to an object. A pointer can:
In a production interview, always connect the specification rule to its concrete runtime consequence: state what lives on the stack versus the heap or static storage segment, how the compiler or operating system validates alignments, lifetimes, and error codes, and what happens under adversarial or boundary inputs (such as zero-length buffers, integer overflow, concurrent mutation, or partial I/O). Backing your explanation with a small trace of register/memory state transitions immediately separates senior systems engineers from candidates who only memorized syntax.
What the interviewer is listening for
- Mastery of core invariant: Contrast what assignment does to a reference and to a pointer.
- Mastery of core invariant: Choose a value, a reference or a pointer for a parameter or a return type.
- Mastery of core invariant: Explain why nullptr replaces 0 and NULL.
- Hardware and ABI awareness: Explaining how sizes, alignments, calling conventions, or kernel boundaries behave on real 64-bit targets rather than relying on implementation-defined assumptions.
- Defensive engineering: Naming the exact compiler flags (
-Wall -Wextra -Werror), static analyzers, or runtime sanitizers (-fsanitize=address,undefined,thread) that verify correctness in CI.
Common mistakes
- Explaining only surface syntax without tracing the underlying memory addresses, ownership lifetime, or kernel/user-space state transitions.
- Assuming undefined behavior (such as signed overflow, uninitialized reads, strict-aliasing violations, or dangling pointers) will "just work" because it passed an unoptimized
-O0debug build. - Ignoring return codes, partial reads/writes, alignment padding, or cleanup paths when an allocation or syscall fails midway through a function.