Early binding and Late binding in C++

Binding refers to the process of converting identifiers (such as variable and performance names) into addresses. Binding is done for each variable and functions. For functions, it means that matching the call with the right function definition by the compiler. It takes place either at compile time or at runtime.

cpp-binding

Early Binding (compile-time time polymorphism) As the name indicates, compiler (or linker) directly associate an address to the function call. It replaces the call with a machine language instruction that tells the mainframe to leap to the address of the function.

By default early binding happens in C++. Late binding (discussed below) is achieved with the help of virtual keyword)

// CPP Program to illustrate early binding.
// Any normal function call (without virtual)
// is binded early. Here we have taken base
// and derived class example so that readers
// can easily compare and see difference in
// outputs.
#include<iostream>
using namespace std;
  
class Base
{
public:
    void show() { cout<<" In Base \n"; }
};
  
class Derived: public Base
{
public:
    void show() { cout<<"In Derived \n"; }
};
  
int main(void)
{
    Base *bp = new Derived;

    // The function call decided at 
    // compile time (compiler sees type
    // of pointer and calls base class
    // function.
    bp->show();  

    return 0;
}

Output:

In Base

Late Binding : (Run time polymorphism) In this, the compiler adds code that identifies the kind of object at runtime then matches the call with the right function definition (Refer this for details). This can be achieved by declaring a virtual function.

// CPP Program to illustrate late binding
#include<iostream>
using namespace std;
  
class Base
{
public:
    virtual void show() { cout<<" In Base \n"; }
};
  
class Derived: public Base
{
public:
    void show() { cout<<"In Derived \n"; }
};
  
int main(void)
{
    Base *bp = new Derived;
    bp->show();  // RUN-TIME POLYMORPHISM
    return 0;
}

Output:

In Derived




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