Menu
Is std::map copy assignment (in style map1 = map2;) required to copy comparator of map2 to map1?
I have tested that actual implementations do that. I am more interested about where in C++ standard it is specified.
838
Method 2 – using the set of pairs The idea is to insert all the (key-value) pairs from the map into a set of pairs that can be constructed using a comparator function that orders the pairs according to the second value. Multimap is similar to a map with an addition that multiple elements can have the same keys.
The default comparator for map sorting is less. Comparator is a type whose name is the third argument of the map declaration, of the map template specialization. This type can be a struct or a class, whose possibly only member, is a custom operator definition.
std::map is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function Compare . Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as red-black trees.
If you mean std::map , it stores pairs of values. In each pair, the first value is called the key, and can be used to quickly look up the associated other value.
If we look at [associative.reqmts]/12 we have
When an associative container is constructed by passing a comparison object the container shall not store a pointer or reference to the passed object, even if that object is passed by reference. When an associative container is copied, either through a copy constructor or an assignment operator, the target container shall then use the comparison object from the container being copied, as if that comparison object had been passed to the target container in its constructor.
emphasis mine
So, in your example, map1 will get a copy of map2's comparator.
89
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
