How do you choose a standard exception and shape a custom type?

A strong answer

A strong candidate frames How do you choose a standard exception and shape a custom type? around the exact memory layout, compiler semantics, and hardware execution model covered in Standard Exceptions and Custom Exception Types. Select invalid_argument and out_of_range correctly, derive focused types, and keep what and order exact.

The base program for this lesson, 0_Language/exception_handling/exception_handling.cpp, ends with a NegativeNumberException derived from std::exception whose what returns a fixed message. Earlier drafts in the same file throw an int and a std::runtime_error for division by zero. Three styles in one file illustrate the maintenance problem from the hook: each call site must remember which shape to catch, and a handler that catches int will miss the class type entirely.

A standard exception is a library type for a common failure: std::invalid_argument for bad parameters, std::out_of_range for index violations, std::runtime_error for failures detectable only at run time. A custom exception is a project type derived from one of those, adding a name that call sites can target. As shown in the trace above, the same throw is handled precisely when the derived clause comes first and coarsely when only the base remains.

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: Select standard exceptions for invalid arguments and range failures.
• Mastery of core invariant: Derive custom exceptions with correct noexcept overrides.
• Mastery of core invariant: Order catch handlers to preserve derived-type information.
• 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 -O0 debug build.
• Ignoring return codes, partial reads/writes, alignment padding, or cleanup paths when an allocation or syscall fails midway through a function.