Constant Member Functions

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本文深入探讨了C++中常成员函数的概念、声明方法及使用案例，通过具体实例展示了如何在类中定义只读操作，确保代码的安全性和一致性。

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Constant Member Functions

Visual Studio 2013

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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. A constant member function cannot modify any non-static data members or call any member functions that aren't constant.

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.

Example

 
     
 
       
 
        // constant_member_function.cpp
class Date
{
public:
   Date( int mn, int dy, int yr );
   int getMonth() const;     // A read-only function
   void setMonth( int mn );   // A write function; can't be const
private:
   int month;
};

int Date::getMonth() const
{
   return month;        // Doesn't modify anything
}
void Date::setMonth( int mn )
{
   month = mn;          // Modifies data member
}
int main()
{
   Date MyDate( 7, 4, 1998 );
   const Date BirthDate( 1, 18, 1953 );
   MyDate.setMonth( 4 );    // Okay
   BirthDate.getMonth();    // Okay
   BirthDate.setMonth( 4 ); // C2662 Error
}
 
       