Cpp Const Pointer Demo

Makefile

run: test_const_pointers.o
	./test_const_pointers.o

test_const_pointers.o: test_const_pointers.cpp
	g++ test_const_pointers.cpp -o test_const_pointers.o -std=c++11

clean:
	rm *.o

test_const_pointers.cpp

#include <assert.h>

class Number {
public:
  int _number;
  Number(int num) : _number(num) {}

  void add(Number *n) { _number = _number + n->_number; }

  bool equals(Number *n) { return n->_number == _number; }
};

int const_pointer_ex(Number *const n) {
  Number new_n(5);
  *n = new_n;
  // n++; // produces compile error
  return 0;
}

int pointer_to_const_value_ex_1(Number const *n) {
  Number new_n(5);
  // *n = *new_n; // REVIEW: produces compile error
  n++;
  return 0;
}

int pointer_to_const_value_ex_2(const Number *n) {
  Number new_n(5);
  // n->add(new_n); // REVIEW: produces compile error
  n++;
  return 0;
}

int const_pointer_to_const_value_ex(const Number *const n) {
  Number new_n(5);
  // n->add(new_n); // REVIEW: produces compile error
  // n++; // REVIEW: produces compile error
  return 0;
}

int const_reference_ex(const Number &n) {
  const Number new_n(5);
  // n.add(new_n); // REVIEW: compile error
  // n = new_n; // REVIEW: compile error
  return 0;
}

int main() {
  Number n20_i(20);
  const_pointer_ex(&n20_i);
  Number n5_e(5);
  assert(n20_i.equals(&n5_e));

  Number n40_i(40);
  pointer_to_const_value_ex_1(&n40_i);
  Number n40_e(40);
  assert(n40_i.equals(&n40_e));

  Number n30_i(30);
  pointer_to_const_value_ex_2(&n30_i);
  Number n30_e(30);
  assert(n30_i.equals(&n30_e));
  return 0;
}