C++ Facade Pattern Example

In this article, we will learn how to use and implement the Facade Pattern in C++ with an example.

Definition - Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. The pattern has a structural purpose and applies to objects.

C++ Facade Pattern Example

#include <iostream>

/*
 * Subsystems
 * implement more complex subsystem functionality
 * and have no knowledge of the facade
 */
class SubsystemA
{
public:
    void suboperation()
    {
        std::cout << "Subsystem A method" << std::endl;
    }
};

class SubsystemB
{
public:
    void suboperation()
    {
        std::cout << "Subsystem B method" << std::endl;
    }
};

class SubsystemC
{
public:
    void suboperation()
    {
        std::cout << "Subsystem C method" << std::endl;
    }
};

/*
 * Facade
 * delegates client requests to appropriate subsystem object
 * and unified interface that is easier to use
 */
class Facade
{
public:
    Facade() : subsystemA(), subsystemB(), subsystemC() {}

    void operation1()
    {
        subsystemA->suboperation();
        subsystemB->suboperation();
    }

    void operation2()
    {
        subsystemC->suboperation();
    }

private:
    SubsystemA *subsystemA;
    SubsystemB *subsystemB;
    SubsystemC *subsystemC;
};


int main()
{
    Facade *facade = new Facade();

    facade->operation1();
    facade->operation2();
    delete facade;

    return 0;
}

Output

Subsystem A method
Subsystem B method
Subsystem C method

When to use?

  • you want to provide a simple interface to a complex subsystem
  • there are many dependencies between clients and the implementation classes of an abstraction
  • you want to layer your subsystems, use a facade to define an entry point to each subsystem level

Comments