why insert to map does not change value

Question

Please refer below code:

https://code.sololearn.com/cA9A8a20a189/#cpp

as we know , adding duplicate key does not change value into map element, but accessing it through key can modify it. Why so?

I mean why duplicate insertion of key does not change value?

Answer 1

https://code.sololearn.com/cY66Zwmo8bxK/?ref=app
If you look at this code it seems like that when you insert already existing key then it is not inserted at all
But changing value at key access that key and change its value

Answer 2

Sometimes you need one or the other behavior so both exist.

Semantically, since a map only contains unique keys, inserting a new key value pair should not work when there already is a value for that key in the map. On the other hand when directly accessing the value for a specific key in the map you should be able to modify it.