Help me with C++ constructors please. Thank you

Question

I wonder what's the reason for my output here. The first line should be all 0s but it's not. The second line is not much meaningful. Actually what does default constructors do?
https://code.sololearn.com/c7y54PeptO1d/?ref=app

Answer 1

According to language rules, the Date constructor qualifies as a trivial default constructor, which actually performs no action. See:

https://en.cppreference.com/w/cpp/language/default_constructor

Since you don't provide an initializer for "today", default-initialization is performed, which just selects and calls the trivial default constructor. As a result, the member variables end up uninitialized. See:

https://en.cppreference.com/w/cpp/language/default_initialization

If you want to zero-initialize a Date object, use value-initialization instead, i.e.

Date today{};

See:

https://en.cppreference.com/w/cpp/language/value_initialization

Answer 2

Shadow thank you I got it!