Constant Member Functions

最新推荐文章于 2019-10-27 21:30:28 发布

转载最新推荐文章于 2019-10-27 21:30:28 发布 · 924 阅读

本文介绍了C++中常量成员函数的概念及使用方法。通过示例详细解释了如何声明和定义常量成员函数，以及它们如何确保不修改所属对象的状态。同时展示了常量成员函数在实际编程中的应用。

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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.

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.

// 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
}