How to use static data members and static member functions of C++ class

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Static data member

Declare with the keyword static

When a data member of a class is declared static, no matter how many objects of the class are created, the static member has only one copy.

Shared among all objects of the class, with static lifetime

If there are no other initialization statements, all static data members are initialized to zero when the first object is created

Defined and initialized outside the class, using the range parsing operator (::) to indicate the class to which it belongs

For example:

# include using namespace std;class Box {public: static int count; / / if the static data member is declared in the private section, Box can only be processed through static member functions (double l = 2.0, double b = 2.0, double h = 2.0) {cout