Virtual Interface

README.md

@@ -28,6 +28,8 @@ Examples include (and will expand to):
 * Performance‑oriented C++ idioms
 * Algorithms
     * [integer-factorization](./integer-factorization/)
+* OOP
+    * [virtual-interface](./virtual-interface/)
 
 ---
 

virtual-interface/Makefile

@@ -0,0 +1,29 @@
+# pull in shared compiler settings
+include ../common.mk
+
+# per-example flags
+# CXXFLAGS += -pthread
+
+TARGET := $(notdir $(CURDIR))
+SRCS   := $(wildcard *.cpp)
+OBJS   := $(SRCS:.cpp=.o)
+
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CXX) $(CXXFLAGS) -o $@ $^
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+run: $(TARGET)
+	./$(TARGET) $(ARGS)
+
+clean:
+	rm -f $(OBJS) $(TARGET)
+
+# Delegates to top-level Makefile
+check-format:
+	$(MAKE) -f ../Makefile check-format DIR=$(CURDIR)
+
+.PHONY: all clean run check-format

virtual-interface/main.cpp

@@ -0,0 +1,59 @@
+/**
+    This example shows the interface using virtual functions in C++.
+*/
+
+#include <iostream>
+#include <memory>
+
+class Shape
+{
+  public:
+    virtual double
+    area() const = 0;   // Pure virtual function
+    virtual ~Shape() {} // Virtual destructor
+};
+
+class Circle : public Shape
+{
+  private:
+    double radius;
+
+  public:
+    Circle(double r) : radius(r) {}
+    double
+    area() const override
+    {
+        return 3.14159 * radius * radius;
+    }
+};
+
+class Rectangle : public Shape
+{
+  private:
+    double width, height;
+
+  public:
+    Rectangle(double w, double h) : width(w), height(h) {}
+    double
+    area() const override
+    {
+        return width * height;
+    }
+};
+
+int
+main()
+{
+    std::unique_ptr<Shape> shapes[2];
+    shapes[0] = std::make_unique<Circle>(5.0);
+    shapes[1] = std::make_unique<Rectangle>(4.0, 6.0);
+
+    // The following line would cause a compilation error because Shape is an abstract class
+    // Shape a = new Shape();
+
+    for (int i = 0; i < 2; ++i) {
+        std::cout << "Area of shape " << i + 1 << ": " << shapes[i]->area() << std::endl;
+    }
+
+    return 0;
+}