Constant Member Functions
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.
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
}