What is function overriding in C plus plus?

Answer 1

Overloading means to provide more than one function with the same function name in the same namespace. Overloaded functions must differ in the number and/or type of arguments they accept. The number and type of arguments constitutes the function signature, which is used to differentiate them. That is, the number and type of arguments you pass determine which instance of the function is called. The return value is not part of the signature, thus overloads cannot differ by return type alone.

Overriding relates to virtual functions where derived classes can provide more specialised implementations of generic methods. When you call the generic base class method implicitly, the most-derived override is called automatically, thus ensuring polymorphic behaviour; objects behave according to their actual type, even when the actual type cannot be determined in advance and without the need for expensive runtime type information. While a base class may be designed to be aware of some of its derivatives, it cannot be made aware of all its derivatives since new derivatives could be created at any time, by anyone with access to the base class definition. Overriding virtual functions ensures that base classes do not need to know anything about any of their derivatives, thus reducing the need for unnecessary coupling.

Answer 2

Overloading a method means to provide the same method name with different signatures, to cater for all the different parameter types that may be passed to a method. Overriding means to provide a new implementation of an existing method, inherited from a base class. Overloaded methods can also be overridden.

Answer 3

Function overloading is where a function with the same name has different signatures.

For example, if you wish to determine the larger of two numbers, you might create the function:

int Max(const int x, const int y)

{

return x > y ? x : y;

}

But what if you also need to compare two floats? You overload the function by creating another function with the same name, but with a different signature:

float Max(const float x, const float y)

{

return x > y ? x : y;

}

Of course there are better ways to achieve the same end (using a macro, for instance), however that's essentially how we overload functions.

Generally, you will overload functions (or methods) within a class. The return type is generally the same for every overload, but the parameters must be different.

Note that signatures cannot differ by return type alone because the compiler has no way of knowing which overload you actually want to call. The best way around this is to write a new method or function using an unique name for each return type you require.

Answer 4

Function overloading applies only to functions within the same namespace, where all the overloads share the same function name, but differ in the number and/or type of arguments. Overloads can also return different types, but cannot differ by return type alone.

Function overriding applies only to class hierarchies, where a derived class overrides the base class behaviour by providing a more specialised implementation of the base class method. Unlike function overloading, the derived class function signature, including the return type, must be covariant with the prototype declared in the base class, including any and all uses of the const keyword.

Classes can also overload their methods. This can sometimes cause problems with derived classes that override some but not all of the overloads in a base class, because the non-overridden methods are effectively hidden from the derived class. They are actually still accessible but because the derived class doesn't provide an explicit interface to those methods, they must be called explicitly via the base class instead.

Note that although function overriding is closely related to virtual functions, it is not necessary to declare a base class function virtual in order for a derivative to override it. A derivative can override any base class function, whether it is declared virtual or not. However, declaring all the override-able methods of a base class as being virtual ensures the most-derived override is always implicitly called, regardless of where the call originated (especially if the call originates from or via one of the base classes). This ensures correct and expected behaviour at all times, but is vital in the case of base class destructors which must always be declared virtual to ensure the entire class is destroyed in the correct sequence.

Answer 5

Function overloading is used when you have to perform a task, but the way to perform the task depends on the number of inputs.

For example: you want to write a function to calculate the area of a rectangle (length and breadth are needed), but user wants to find the area of a square (only length is needed). In such cases, function overloading is used.

int area(int l, int b)

{

return (l*b);

}

int area(int a)

{

return (a*a);

}

In this case the function "area" is overloaded and the user can calculate the area of square or rectangle as per the need.

Answer 6

Function overriding is where a derived class provides a more-specialised implementation for a base class method. Although a derived class may override any base class method, only those methods declared virtual in the base class are expected to be overridden while those declared pure-virtual must be overridden. Failure to implement a pure-virtual method results in an abstract class, but once implemented, the function is implicitly virtual rather than pure-virtual. Overriding a non-virtual method hides the base class method along with any other overrides defined in the base class, rendering them completely inaccessible to the derived class. To keep them visible, do not override any non-virtual methods, use an unique name for the method instead.

Answer 7

Function overriding in C++ is when you declare and define a second function having the same name as the first function, but differing in the number and/or types of arguments. The compiler decides which function to call based on the signature of the arguments.

Answer 8

They sound very similar and they do quite similar things, but they are, in fact, quite distinct. Both involve creating new functions with the same name as existing functions. But there the similarity ends.

The main difference relates to a function's signature. That is; the number and type of parameters the function accepts, including the return type and the use of the const keyword. Parameters and return types that are covariant (are derivative) are said to be same. Note that functions cannot differ by return type alone.

If the signatures are the same, we are said to be overriding the function.

If the signatures differ in any way, we are said to be overloading the function.

It is also possible to combine the two such that we can override an overloaded function, as well as overload an overridden function.

Overloading a function allows us to call the same function name but with different parameter types, even if the only difference is to include the keyword const in one version but not the other. For instance, we might provide a function that accepts an integer, and overload it by adding another that accepts a float. They are the same function in name only; they have completely separate implementations. The compiler determines which version to call by the type of parameter we pass to the function.

Overrides are a little more complex. We obviously cannot have two functions with the same name and signature within the same namespace, but we can if they each reside in a separate namespace. This introduces an ambiguity; if the signatures are the same, the compiler will not know which version to call. We resolve this by explicitly qualifying the namespace of the function we wish to invoke.

Overrides (as well as overloads) are more commonly found in class hierarchies, where we derive new classes from existing base classes. Ambiguities still exist but the inclusion of virtual functions (functions we expect to be overridden by derived classes) ensure that the correct override is called without us having to make explicit calls to them. This is known as polymorphism. However we can still make explicit calls when required, such as when calling base class methods that are declared virtual (we often use explicit calls to invoke base class methods in an override, in order to augment that method, rather than replace it entirely).

One problem programmers often encounter is that if we override an overloaded base class method, we effectively hide all the overloads in the base class from the derived class. If we want to access all the overloads from a derived class, we must override all those overloads. Similar behaviour occurs when dealing with class constructors; if we don't define any constructor then we automatically inherit a default constructor during compilation. But if we define any constructor, the compiler will no longer generate that default constructor. The compiler will still generate a copy constructor, however, unless we choose to override it with our own.

Answer 9

Function overloading simply means declaring two or more functions within the same namespace, with the same name but with different signatures. A function's signature is defined by the number and type of arguments it accepts, thus functions cannot differ by return type alone.

Function overloading is achieved through prototyping the functions. A function's prototype is a declaration of the function name, its return type and its parameter types (if any). The compiler uses the prototype to determine which version of an overloaded function you are calling, and can notify you whenever no prototype matches a particular function call, which is usually an indication of a user-error or a typo.