/ Design Patterns / Structural patterns / Proxy

Proxy Design Pattern in C++

"A protection proxy controls access to the original object"

class Person
{
    string nameString;
    static string list[];
    static int next;
  public:
    Person()
    {
        nameString = list[next++];
    }
    string name()
    {
        return nameString;
    }
};
string Person::list[] = 
{
  "Tom", "Dick", "Harry", "Bubba"
};
int Person::next = 0;

class PettyCashProtected
{
    int balance;
  public:
    PettyCashProtected()
    {
        balance = 500;
    }
    bool withdraw(int amount)
    {
        if (amount > balance)
          return false;
        balance -= amount;
        return true;
    }
    int getBalance()
    {
        return balance;
    }
};

class PettyCash
{
    PettyCashProtected realThing;
  public:
    bool withdraw(Person &p, int amount)
    {
        if (p.name() == "Tom" || p.name() == "Harry" || p.name() == "Bubba")
          return realThing.withdraw(amount);
        else
          return false;
    }
    int getBalance()
    {
        return realThing.getBalance();
    }
};

int main()
{
  PettyCash pc;
  Person workers[4];
  for (int i = 0, amount = 100; i < 4; i++, amount += 100)
    if (!pc.withdraw(workers[i], amount))
      cout << "No money for " << workers[i].name() << '\n';
    else
      cout << amount << " dollars for " << workers[i].name() << '\n';
  cout << "Remaining balance is " << pc.getBalance() << '\n';
}

Output

100 dollars for Tom
No money for Dick
300 dollars for Harry
No money for Bubba
Remaining balance is 100

Code examples

Java Proxy in Java
C++ Proxy in C++: Before and after Proxy in C++ Proxy in C++
PHP Proxy in PHP
Python Proxy in Python