class B : public Aclass C : public Bclass C : public A, public B┌───────────┐
│ Device │
└─────┬─────┘
┌────┴────┐
┌─────┴───┐ ┌───┴─────┐
│ Printer │ │ Scanner │
└─────┬───┘ └───┬─────┘
└────┬────┘
┌─────┴─────┐
│ Copier │ (Without virtual inheritance: 2 copies of Device!)
└───────────┘class Printer : virtual public Device and class Scanner : virtual public Device, Copier receives only ONE shared instance of Device.#include <iostream>
#include <string>
// Virtual Base Class
class Device {
public:
int deviceId;
explicit Device(int id) : deviceId(id) {
std::cout << "Device(" << deviceId << ") initialized.\n";
}
};
class Printer : virtual public Device {
public:
Printer(int id) : Device(id) {}
void printDocument() { std::cout << "Printing document on device " << deviceId << "\n"; }
};
class Scanner : virtual public Device {
public:
Scanner(int id) : Device(id) {}
void scanDocument() { std::cout << "Scanning document on device " << deviceId << "\n"; }
};
// Most derived class initializes the virtual base
class MultiFunctionPrinter : public Printer, public Scanner {
public:
MultiFunctionPrinter(int id) : Device(id), Printer(id), Scanner(id) {}
};
int main() {
MultiFunctionPrinter mfp(7001);
mfp.printDocument();
mfp.scanDocument();
std::cout << "Shared Device ID: " << mfp.deviceId << "\n"; // Unambiguous!
return 0;
}