问题
What is the default values for members of a struct and members of a class in c++, and how do these rules differ (e.g. between classes/structs/primitives/etc) ? Are there circumstances where the rules about the default values differs ?
回答1:
There are no differences between structs and classes in this regard in C++. They all are called just class types.
Members of class types have no default values in general case. In order to for a class member to get a deterministic value it has to be initialized, which can be done by
- Default constructor of the member itself
- Constructor initializer list of the enclosing class
- Explicitly specified initializer for object of the enclosing class (that includes value-initialization and initialization with aggregate initializer).
Additionally, all objects with static storage duration are zero-initialized at the program startup.
Aside from the above cases, class members, once again, have no default values and will initially contain unpredictable garbage values.
回答2:
Yeah, there is one. If you initialize an object with the default constructor and use parentheses then the POD members will be zero initialized:
someClass * p = new someClass();
来源：https://stackoverflow.com/questions/2614809/what-is-the-default-value-for-c-class-members