What is the difference between emplace and insert?

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**emplace** — constructs element in-place: ```cpp std::vector> v; v.emplace_back(1, "hello"); // constructs pair in-place ``` **insert** — copies/moves existing object: ```cpp v.push_back({1, "hello"}); // constructs temporary, then moves ``` **Performance difference:** - `emplace_back`: one construction - `push_back`: temporary + move - For complex objects, emplace is faster - For trivial types, difference is negligible **When emplace wins:** ```cpp std::set s; s.emplace("long string"); // one allocation s.insert("long string"); // temporary + copy/move ``` **Best practice:** Default to `emplace` for non-trivial types.

C++: What is the difference between emplace and insert?