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I see that the insert method of std::map and std::unordered_map is going to change from
template<class P> std::pair<iterator,bool> insert(P&& value); (C++11)
to
std::pair<iterator,bool> insert(value_type&& value); (C++17)
However, for these containers, value_type is std::pair<A const, int>. Two questions here:
P is default_constructible<value_type, P&&>), then std::pair<A, int> - which is most of the time the type of this argument as it is the one returned by std::make_pair - and can call the move constructor of A. But in the C++17 version, this argument is casted to value_type, where A is const, then non-movable. A has to be copied, if I am not overlooking something. Or does C++17 change anything on that side too? Thanks!
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C++ map update – Simple program example to update value in map. To update an existing value in the map, first we will find the value with the given key using map::find() function. If the key exists, then will update it with new value.
Its time complexity is O(logN). insert( ): insert a single element or the range of element in the map. Its time complexity is O(logN), when only element is inserted and O(1) when position is also given.
std::map::insert succeeds when it inserts the new element, otherwise it returns an iterator to an already existing element.
Why C++ map. insert() doesn't overwrite - Stack Overflow. Stack Overflow for Teams – Start collaborating and sharing organizational knowledge.
An additional non-template overload to insert was added in C++17.
Such an overload has the advantage that it permits .insert( { {key}, {value, args} } ) syntax -- {} based construction. template arguments cannot be passed {} based construction instructions without an explicit type.
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