In this tutorial we are going to study about
- Constant Member Functions
- Mutable Keyword
- Overloading Member Functions
1. Constant Member Functions in C++
Below are few points on Constant Member Functions
- “const” is the keyword to declare a constant member function.
- Once the member function is declared as constant, it cannot modify the data member value in that function.
- We use this in the functions, where we don’t need accidental modification of the data.
Example:
#include <iostream>
using namespace std;
class MyClass
{
int num;
public:
void myFunc() const
{
// error: cannot assign to non-static data member within const member function 'myFunc
//num ++;
cout<<"In const function"<<endl;
}
};
int main(void)
{
static MyClass obj;
obj.myFunc();
return 0;
}Output:
In const function
2. Mutable data members in C++
Below are few points on “mutable” keyword.
- “mutable” keyword is only applicable to data members.
- In some cases, we need to modify a data inside a constant member functions.
- In such cases, we make a data member as mutable, so that it can be modified inside a constant member function.
Example:
#include <iostream>
using namespace std;
class MyClass
{
mutable int iNum;
int num;
public:
void myFunc() const
{
// error: cannot assign to non-static data member within const member function 'myFunc
//num ++;
iNum++; // no error
cout<<"In const function"<<endl;
}
};
int main(void)
{
static MyClass obj;
obj.myFunc();
return 0;
}Output:
In const function
3. Overloading Member Functions in C++
- Function overloading is a feature two or more functions having same name but different parameters.
- This is kind of polymorphism feature of C++
Example:
#include <iostream>
using namespace std;
void fun(int num)
{
cout<<"Int function"<<endl;
}
void fun(double num)
{
cout<<"double function"<<endl;
}
void fun(string num)
{
cout<<"String function"<<endl;
}
int main(void)
{
fun(10);
fun(12.34);
fun("String");
return 0;
}Output:
Int function double function String function
