Differentiate between function overloading and function overriding in C++?
Overloading a method (or function) in C++ is the ability for functions of the same name to be defined as long as these methods have different signatures (different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class.
a) In overloading, there is a relationship between methods available in the same class whereas in overriding, there a is relationship between a superclass method and subclass method.
(b) Overloading does not block inheritance from the superclass whereas overriding blocks inheritance from the superclass.
(c) In overloading, separate methods share the same name whereas in overriding, subclass method replaces the superclass.
(d) Overloading must have different method signatures whereas overriding must have same signature.
Function overloading is done when you want to have the same function with different parameters
void Print(string s);//Print string
void Print(int i);//Print integer
Function overriding is done to give a different meaning to the function in the base class
class Stream//A stream of bytes
{
public virtual void Read();//read bytes
}
class FileStream:Stream//derived class
{
public override void Read();//read bytes from a file
}
class NetworkStream:Stream//derived class
{
public override void Read();//read bytes from a network
}
You are putting in place an overloading when you change the original types for the arguments in the signature of a method.
You are putting in place an overriding when you change the original Implementation of a method in a derived class.
Overriding means, giving a different definition of an existing function with same parameters,
and overloading means adding a different definition of an existing function with different parameters.
Example:
#include <iostream>
class base{
public:
//this needs to be virtual to be overridden in derived class
virtual void show(){std::cout<<"I am base";}
//this is overloaded function of the previous one
void show(int x){std::cout<<"\nI am overloaded";}
};
class derived:public base{
public:
//the base version of this function is being overridden
void show(){std::cout<<"I am derived (overridden)";}
};
int main(){
base* b;
derived d;
b=&d;
b->show(); //this will call the derived overriden version
b->show(6); // this will call the base overloaded function
}
Output:
I am derived (overridden)
I am overloaded
1.Function Overloading is when multiple function with same name exist in a class.
Function Overriding is when function have same prototype in base class as well as derived class.
2.Function Overloading can occur without inheritance.
Function Overriding occurs when one class is inherited from another class.
3.Overloaded functions must differ in either number of parameters or type of parameters should be different.
In Overridden function parameters must be same.
For more detail you can visit below link where you get more information about function overloading and overriding in c++
https://googleweblight.com/i?u=https://www.geeksforgeeks.org/function-overloading-vs-function-overriding-in-cpp/&hl=en-IN
Function overloading is same name function but different arguments. Function over riding means same name function and same as arguments
Function overloading - functions with same name, but different number of arguments
Function overriding - concept of inheritance. Functions with same name and same number of arguments. Here the second function is said to have overridden the first
in overloading function with same name having different parameters whereas in overridding function having same name as well as same parameters replace the base class to the derived class (inherited class)
Function overloading may have different return types whereas function overriding must have same or matching return types.
Overloading means having methods with same name but different signature
Overriding means rewriting the virtual method of the base class.............
In addition to the existing answers, Overridden functions are in different scopes; whereas overloaded functions are in same scope.
Related
As far as I learned, Overriding is when you have 2 functions which have the same name and function return type (void, int, float.. etc) and the same parameter numbers and types.
And the overloading is when you have 2 functions which have the same name but either Parameter number/types or function return type should be different.
But today when I was in the class, I saw this slide:
Shouldn't this be overloading? Not overriding? Because here the return type changed (from void
to float) and fa1() function in the base class had no parameter, but in the derived class it has float parameter.
If this is overriding, why?
In C++, any method in a derived class only overrides the method in the base class if their declarations match (I say "match" but I don't know the formal term for that). That is, all arguments must have the same type, and const qualification of this must be the same. If anything there mismatches, the method in the derived class hides all methods with the same name, instead of overriding. This is what the "ERROR" in your picture tries to tell you. So // overrides in a comment in that picture is incorrect and misleading.
Yes, many C++ teachers actually don't understand these somewhat obscure details.
BTW additionally, if you want to override, the method in your base class should be virtual; otherwise, polymorphism won't work. If it was not virtual, we also say that the derived-class method hides the base-class method. Here, however, the part about hiding has almost no meaning; what this term really wants to express is that you're not overriding.
In addition, overloading is, as you noticed, presence of several methods with the same name but different signatures. They should all be present in the derived class to be useful - if the derived class has only one method fa1, and the other fa1 are in the base, they will be hidden. However, there is syntax sugar which "copies" all fa1 from base to derived, disabling all that hiding semantics:
class A
{
public:
void fa1();
void fa1(int);
};
class B: public A
{
public:
using A::fa1;
void fa1(int, int);
};
...
B b;
b.fa1(); // calls A::fa1()
b.fa1(4); // calls A::fa1(int)
b.fa1(4, 8); // calls B::fa1(int, int)
The part about hiding is rarely, if ever, useful. When overriding, you should tell this to your compiler - use the override keyword for that. The compiler will then check that your code works as you intended.
class A
{
public:
virtual void fa1(int) {}
void fa2(int) {}
};
class B: public A
{
public:
void fa1(int) override {} // OK
void fa1() override {} // ERROR: doesn't really override - different signature
void fa2(int) override {} // ERROR: doesn't really override - not virtual in base
};
ia1 not overloading. First you can't overload variables. So ia1 is definitely an override. And it's also a dangerous thing. At my company, our coding standards disallow overriding variable names in any situation. It just leads to confusion.
fa1 though -- that looks like an overload. The base class fa1() takes no arguments, but the subclass version takes a float.
There is somewhat odd sample given in one of the Microsoft documentation pages , which consists of two classes, one is a base class and another one is a derived. The base class has the following virtual function member:
virtual void setEars(string type) // virtual function
{
_earType = type;
}
And another, defined in the derived class, which, as stated in comments, redefines the virtual function:
// virtual function redefined
void setEars(string length, string type)
{
_earLength = length;
_earType = type;
}
These two have different signatures and I haven't ever heard if you actually can redefine a virtual function with a function of a different signature. I compiled this sample and could find any overriding behavior between these two. Is the sample just misleading or I'm missing something?
Is the sample just misleading or I'm missing something?
This example is indeed misleading.
When overriding a virtual function in a derived type, it must come with the same signature as it is defined in the base class. If that is not the case, the function in the child class will be considered as its own entity and is not considered in a polymorphic function call. Additionally, it will hide the name of the base classes function, which is considered bad practice, as it violates the "is-a" relationship in public inheritance.
In order to prevent such accidental hiding, C++ introduced the override keyword. When overriding a virtual function, it then must have a matching signature, otherwise, the compiler will reject it.
I found there has many definition about polymorphism and overloading. Some people said that overloading is one type of polymorphism. While some people said they are not the same. Because only one function will be allocate in overloading. While the polymorphism need allocate the memory for each redefined member function. I really feel confusion about this, any one could explain this for me?
Further, whether overloading happens at compile time while the polymorphism happens at running time?
Polymorphism is the process to define more than one body for functions/methods with same name.
Overloading IS a type of polymorphism, where the signature part must be different. Overriding is another, that is used in case of inheritance where signature part is also same.
No, it's not true that polymorphism happens in runtime. What happens in runtime is called runtime polymorphism. That is implemented using virtual keyword in C++.
Hope it helped..
The polymorphism is the base of the OOP, the overloading is one of ways to implement to polymorphism, specially when are involved operators. More generally, speaking about polymorphism when there are two or more classes involved. While the overloading can be made also inside the same class, we can overload the name of a method with several signatures (different list of parameters). While overriding is designed exclusively for involving two or more classes. Note that the overrided methods have all the same signature.
this was told by Bjarne Stroustrup in his book,polymorphism is one which a single thing that act in many forms (i.e) A single function that act in many forms with different parameters. since in c++ constructor name have to be same as class name, you cant have different constructors with different name. so to overcome that function overloading came. many people confuse that function overloading is a type of of polymorphism. they are both at different ends they cant be tied together.
You cannot determine whether a method is a polymorphic method, or simply an overridden method based solely upon its signature. You need to see how the method is invoked.
Here is some sample code which may help illuminate the answer:
public class parentClass {
//Overridden method
public void disp()
{
System.out.println("Output: disp() method of parent class");
}
}
public class childClass extends parentClass {
//You cannot determine whether these methods are polymorphic
//or static polymorphic (aka overridden) simply by their signatures.
//It is by the way they are invoked which determines this.
public void disp(){
System.out.println(" Output: disp() method of Child class");
}
public long add(long a, long b){
return a + b;
}
public int add(int a, int b){
return a+b;
}
public String add(String a, String b){
return a + b;
}
public static void main( String args[]) {
//Here a child class has overridden the disp() method of the
//parent class. When a child class reference refers to the child
//class overriding method this is known as static polymorphism
//or more simply, overriding.
System.out.println("childClass referencing the childClass's overridden, or static polymorphic method");
childClass myChildObj = new childClass();
myChildObj.disp();
//Another example of static polymorphic, or overridden methods
System.out.println("The following are overridden, or static polymorphic methods:");
System.out.printf(" Long add()override method results: %d \n",
myChildObj.add(5999999, 1));
System.out.printf(" Integer add() override method results: %d \n", myChildObj.add(3,2));
System.out.printf(" String add() override method results: %s \n",
myChildObj.add(" First and ...", " Second"));
//When the parent class reference refers to the child class object
//then the overriding method is called.
//This is called dynamic method dispatch and runtime polymorphism
System.out.println("True polymorphism, when the parent class object calls the child class's method:");
parentClass myParentObj = new childClass();
myParentObj.disp();
}
}
The expected output:
childClass referencing the childClass's overridden, or static polymorphic method
Output: disp() method of Child class
The following are overridden, or static polymorphic methods:
Long add()override method results: 6000000
Integer add() override method results: 5
String add() override method results: First and ... Second
One example of true polymorphism, when the parent class object calls the child class's method:
Output: disp() method of Child class
The word itself exlains the clear meaning. 'Poly' means multiple, while 'morphism' (used in image technology) means the process of gradual change from one form to another. Thus, same thing will have different forms.
Technically, Polymorphism is way of implementing 'Single Interface (Skeleton or structure) multiple Implementation (content or body)'. Polymorphism is a general term which refers to both overloading and overriding. Overloading is done in same class where the functions or methods with the same name have different signatures (argument list or return type) while overriding comes in picture in case of inheritance where a function interface, in the Super class, has similar interface in the subclass and has different implementation than the one in super class.
The Super class and sub class form a hierarchy moving from lesser specialization to greater specialization and this should always be remembered while implementing overriding of functions.
Function overloading takes place with functions having same name, but with different parameters.
In polymorphism the functions having same name are chosen based on its objects.
Polymorphism is based on following 2 concepts:
Overloading(Compile-Time polymorphism): Methods with same name but different operation
Overriding(Run-Time polymorphism): Override a method in base class by creating similar method in derived class
-Corrected the Explainations
Shyam Kodase
Overloading is just a way of providing multiple ways of calling the same method/function/constructor with default values, less arguments etc.
Polymorphism is about object inheritance, sub classes etc.
Say if I have an interface with virtual methods, but one of the arguments are:
virtual void Delete(ParentClass *parentClass) = 0;
If I later implement this in child class
void Delete(ChildClass *childClass)
{
};
...why doesn't this work as an implementation?
As the function prototype differs (one uses ParentClass and the other ChildClass) they are not the same functions. Instead the one with the ChildClass argument is overloading and not overriding the Delete function.
C++03 Standard: 10.3/2
If a virtual member function vf is declared in a class Base and in a class Derived, derived directly or indirectly from Base, a member function vf with the same name and same parameter list as Base::vf is declared, then Derived::vf is also virtual an it overrides Base::vf.
Note the text in bold.
An derived class function overides a Base class function only and only if it has the same signature as the Base class function with the exception of Co-Variant return types. Since your function Delete() does not have the same signature in Base Class and Derived class, the derived class function is not overidding the Base class function but what you get is merely Function Hiding.
C++03 Standard: 3.3.7/1:
A name can be hidden by an explicit declaration of that same name in a nested declarative region or derived class.
Because any type that's accepted as an argument for the base-class function, must also be acceptable by an override of that function. This prevents an error such as:
struct BastardClass : ParentClass {} wrong;
Delete(&wrong);
which, if dispatched to the override that expects a ChildClass, would cause it to interpret the object as the wrong type.
(This is known as contravariance - arguments to a function overridden by a more specific type must be no more specific than those being overridden. For similar reasons, return types must be covariant - those specified by a function overridden by a more specific type must be no less specific.)
What is the main difference between operator overloading and operator overriding in C++?
Some use the latter term to describe what's being done when you defined an own global operator new or operator delete. That's because your own definition can replace the default version in the library. The C++ Standard uses the words replaces and displaces for this. Using "override" is a bit confusing because that term is already used for virtual functions being overridden by a function in a derived class.
The term "overloading" is the general term used for defining your own operator functions. This term is used even if no actual overloading happens by the operator function. One way to approach this term is because it "overloads" the built-in meaning of certain operators.
I've never heard the latter term, though I'd assume it'd be the same as the first one. Operator overloading is where you provide a function for a class to behave when used in an operator context. For example, if I had a class point, and wanted to add them such as a + b, I'd have to create an operator+(point other) function to handle this.
In general overloading is used to identify when there is more than one signature for a given function name. Each such defined function is an overload of the function name. On the other hand override is present only in polymorphic (virtual in C++) member functions, where a redefinition of the same signature in a derived method overrides the behavior provided in the base class.
struct base {
virtual void foo();
void foo(int); // overloads void foo()
};
struct derived : base {
void foo(); // overrides void base::foo()
void foo(int); // overloads void derived::foo()
// unrelated to void::base(int)
};
int main() {
derived d;
base & b = d;
b.foo( 5 ); // calls void base::foo(int)
b.foo(); // calls the final overrider for void base::foo()
// in this particular case void derived::foo()
d.foo( 5 ); // calls void derived::foo(int)
}
Nice homework question. I'll help you here... Overloading means 2 methods with the SAME Name and different signatures + return types. Overriding means 2 methods with the SAME name, wherein the sub method has different functionality. Examples fall on you for this exercise.
if the question is regarding function overloading and function overriding then...
#woot4moo has explained that thing .
As far as my knowledge is concerned i have never heard of "operator overriding".
operator overloading is done to provide your class's object with special functionality related to that operator , whenever that operator is to be used with the object .
For example a class should provide an operator(=) to always prevent shallow coping.(well that is done in conjunction with a copy constructor).
I guess "operator overriding" applies when you declare an operator inside a class and make it virtual. That is a very fragile thing to do - you're usually better off doing something else.
The main difference between overloading and overriding is
that in overloading we can use same function name with
different parameters for multiple times for different tasks
with on a class.
and overriding means we can use same name function name
with same parameters of the base class in the derived class.
this is also called as re useability of code in the programme.
If derive class define same function as base class then it is known as overriding.
When name of function is same but different arguments are use to difine the function are overloading.