Containers for containers.

What this C++ nested-container question tests

This is an easy C++ language-knowledge question that probes your familiarity with how the compiler handles template syntax, particularly when dealing with containers of containers. It is the kind of question that separates candidates who have practical C++ experience from those who have only studied it in theory.

The question asks you to trace through code and predict its output—or identify a compilation failure. Success requires understanding how the compiler parses template angle brackets, the behaviour of standard library containers when nested, and any quirks or gotchas that arise from the specific C++ standard in use. These details matter in real codebases, especially in high-frequency trading environments where C++ is the language of choice.

• Template instantiation and parsing
• Nested container initialization and semantics
• Compiler error messages and template syntax edge cases