const

const成员函数必须在声明和定义时都注明const

Declaring a member function with the const keyword specifies that the function is a "read-only" function that does not modify
the object for which it is called.
To declare a constant member function, place the const keyword after the closing parenthesis of the argument list.
The const keyword is required in both the declaration and the definition. A constant member function cannot modify any data members
or call any member functions that aren't constant.

 const member variable can only be initialized in constructor initialization list.

下例用来说明：

1）const成员函数不能修改成员变量

2）非const成员函数可以访问const和非const成员变量，但不能修改const成员变量

class Base_const{public:void fun() const;void nonconst_fun_access_const_var();Base_const(int x):i(1),c(x) {}private:int i;const int c;};void Base_const::fun() const{//i=4; //const成员函数不能修改成员变量cout << "i= "<<i <<endl<<"c=" << c <<endl;nonconst_fun();//error: non_const function can't be called by const function};//非const成员函数可以访问const和非const成员变量，但不能修改const成员变量void Base_const::nonconst_fun(){c++; //error:不能修改const成员变量i++;cout << c <<endl;cout << i <<endl;}#endif /* MYCONST_H_ */