Count how many times class member was printed-CodePudding

I need to count how many times class members were printed using function Print which is inspector. Constructor should set private elements of class.

#include <cmath>
#include <iostream>
class Vector3d {
  double x, y, z;
  mutable int count = 0;
  public:
    Vector3d();
  Vector3d(double x, double y, double z);
  void Print() const;
  int GetCount() const;
};
Vector3d::Vector3d() {
  count = 0;
}
Vector3d::Vector3d(double x, double y, double z) {
  count = 0;
  Vector3d::x = x;
  Vector3d::y = y;
  Vector3d::z = z;
}
void Vector3d::Print() const {
  count  ;
  std::cout << "{" << x << "," << y << "," << z << "}";
}
int Vector3d::GetCount() const {
  return count;
}
int main() {
  Vector3d v1(1, 2, 3);
  v1.Print();v1.Print();v1.Print();
  Vector3d v2(v1);
  v2.Print();v2.Print();
  std::cout << v2.GetCount();
  return 0;
}

I used mutable int to enable changing element of const function. For v1.GetCount() I get output 3, which is correct. However, for v2.GetCount() I get output 5, which is wrong (correct is 2).

Could you help me to fix this? Where am I making mistake?

CodePudding user response：

You need to overload copy constructor and copy assign operator for Vector3d class. Now you are copying state of count field into v2 object, therefore it starts from 3 not from 0.

#include <cmath>
#include <iostream>
class Vector3d {
    double x, y, z;
    mutable int count = 0;
public:
    Vector3d(double x, double y, double z);
    Vector3d(const Vector3d&);
    Vector3d& operator=(const Vector3d&);
    Vector3d(Vector3d&&) = delete;
    Vector3d& operator=(Vector3d&&) = delete;
    void Print() const;
    int GetCount() const;
};
Vector3d::Vector3d(double x, double y, double z) {
    Vector3d::x = x;
    Vector3d::y = y;
    Vector3d::z = z;
}
Vector3d::Vector3d(const Vector3d& that)
: Vector3d(that.x, that.y, that.z)
{
}
Vector3d& Vector3d::operator=(const Vector3d& that)
{
    x = that.x;
    y = that.y;
    z = that.z;
    return *this;
}

void Vector3d::Print() const {
    count  ;
    std::cout << "{" << x << "," << y << "," << z << "}";
}

int Vector3d::GetCount() const {
    return count;
}

int main() {
    Vector3d v1(1, 2, 3);
    v1.Print();v1.Print();v1.Print();
    Vector3d v2(v1);
    v2.Print();v2.Print();
    std::cout << v2.GetCount();
    return 0;
}

UPDATE: Someone mentioned that explicitly deleted move ctor and operator is not ok, I understand that, but for me it is not clear should we move counter to other instance or not. Therefore here possible implementation:

#include <cmath>
#include <iostream>

class Vector3d {
    double x, y, z;
    mutable int count = 0;
public:
    Vector3d(double x, double y, double z);
    Vector3d(const Vector3d&);
    Vector3d(Vector3d&&);
    Vector3d& operator=(Vector3d);
    void Print() const;
    int GetCount() const;

private:
    void swap(Vector3d&);
};
Vector3d::Vector3d(double x, double y, double z) {
    Vector3d::x = x;
    Vector3d::y = y;
    Vector3d::z = z;
}
Vector3d::Vector3d(const Vector3d& that)
        : Vector3d(that.x, that.y, that.z)
{
}
Vector3d::Vector3d(Vector3d&& that)
: Vector3d(that.x, that.y, that.z)
{
    count = that.count;
}
Vector3d& Vector3d::operator=(Vector3d that)
{
    swap(that);
    return *this;
}

void Vector3d::swap(Vector3d& that)
{
    std::swap(x, that.x);
    std::swap(y, that.y);
    std::swap(z, that.z);
    std::swap(count, that.count);
}

void Vector3d::Print() const {
    count  ;
    std::cout << "{" << x << "," << y << "," << z << "}";
}

int Vector3d::GetCount() const {
    return count;
}

int main() {
    Vector3d v1(1, 2, 3);
    v1.Print();v1.Print();v1.Print();
    Vector3d v2 = std::move(v1);
    v2.Print();v2.Print();
    std::cout << v2.GetCount();
    return 0;
}

But these more for commenters than for question author.