How does the compiler choose among overloaded functions?

A strong answer

A strong candidate frames How does the compiler choose among overloaded functions? around the exact memory layout, compiler semantics, and hardware execution model covered in Overloading and Default Arguments. Explain overload ranking, ambiguous calls, name mangling, and when default arguments are filled in.

You want a function show that prints an int, a double or a bool. Languages without overloading force a name per type: showInt, showDouble, showBool. You also want functions with optional details, such as a greeting that is "Hello" unless the caller says otherwise.

C++ solves both. You have already used the first idea without noticing: std::cout << 65 prints 65, while std::cout << 'A' prints A. Both values are the same number, as lesson 4 explained, and the stream prints them differently because it has a separate insertion function for int and for char. The compiler picks the right one from the type of the argument. This lesson explains how that choice works.

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: Predict which overload the compiler picks for a given call.
• Mastery of core invariant: Explain why overloading costs nothing at run time and how the linker tells overloads apart.
• Mastery of core invariant: Use default arguments correctly and explain when they are filled in.
• 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.