Why I get this warning? "Member 'x' was not initialized in this constructor"

Question

given the following code:

class Class {
    int x;
public:
    Class() = default;
};  

I get the following warning:

Member 'x' was not initialized in this constructor

What is the reason of this warning?

Answer 1

x is an int and its default initialization leaves it with an indeterminate value. The simplest, most uniform fix is to value-initialize it in its declaration.

class Class {
    int x{}; // added {}, x will be 0
  public:
    Class() = default;
};

You could also do int x = 5; or int x{5}; to provide a default value