24 Containers library [containers]

24.6 Container adaptors [container.adaptors]

24.6.9 Class template flat_map [flat.map]

24.6.9.5 Capacity [flat.map.capacity]

size_type size() const noexcept;
Returns: c.keys.size().
size_type max_size() const noexcept;
Returns: min<size_type>(c.keys.max_size(), c.values.max_size()).