The following MyTest testObj = {}; is not zero-initialization for MyTest, but is simply calling its default constructor. The cppreference page explains why (emphasis mine): As part of value-initialization sequence for non-class types and for members of value-initialized class types that have no constructors, including value initialization of elements of aggregates for which no initializers … Read more
On the site you linked it says: When the default allocator is used, this results in the key being copy constructed from key and the mapped value being value-initialized. So the int is value-initialized: The effects of value initialization are: […] 4) otherwise, the object is zero-initialized This is why the result is 0.
I’m a bit confused as to why that last element outside of the array always “defaults” to zero. In this declaration int x[] = {120, 200, 16}; the array x has exactly three elements. So accessing memory outside the bounds of the array invokes undefined behavior. That is, this loop for (int i = 0; … Read more