Copy Constructor called unexpectedly

Question

I am new to C++ programming. I am using Visual Studio Code, my code:

#include <iostream>
using namespace std;

class Calculator;

class Complex
{
    float a, b;
    string Operation;
    string name;

    friend class Calculator;

public:
    Complex(float, float, string, string);
    Complex(float);
    Complex();
    Complex(Complex &, string);

    void PrintComp(string op = "None")
    {
        if (op != "None" && name != "None")
        {
            cout << "\nBy " << op << " of z1 and z2:\n"
                 << name << " = " << a << " + " << b << "i\n";
        }
        else if (name != "None")
        {
            cout << name << " = " << a << " + " << b << "i\n";
        }
        else
        {
            cout << a << " + " << b << "i\n";
        }
    }
};

Complex ::Complex(float x, float y, string givnname = "None", string operation = "None")
{
    a = x;
    b = y;
    name = givnname;
    PrintComp(operation);
}
Complex ::Complex(float x)
{
    a = x;
    b = 0;
}
Complex ::Complex()
{
    a = 0;
    b = 0;
}
Complex::Complex(Complex &obj, string givnname="None")
{
    a = obj.a;
    b = obj.b;
    name = givnname;
    cout << "Copy Cons called!"<< endl;
    PrintComp();
}

class Calculator
{
public:
    float SumRealComp(Complex const&, Complex const&);
    float SumImgComp(Complex const&, Complex const&);
};

float Calculator ::SumRealComp(Complex const &obj1, Complex const & obj2)
{
    return (obj1.a + obj2.a);
}
float Calculator ::SumImgComp(Complex const & obj1, Complex const & obj2)
{
    return (obj1.b + obj2.b);
}

int main()
{
    Complex z1(3, 5, "z1"), z2(4, 4, "z2");

    Calculator calc;

    Complex z3(calc.SumRealComp(z1, z2), calc.SumImgComp(z1, z2), "z3", "Sum");

    Complex z4(z1, "z4");

    return 0;
}

According to above code, I am using copy Constructor at the last, but Copy Constructor is called at formation of every object. Even when args of both are different. Why it is so? I am learning from here.
Every suggestions in my code are appreciated.
Thanks!

`Complex(Complex &, string);` is not a copy constructor; `Complex(Complex const &);` is the expected signature for a copy constructor see [Copy constructors](https://en.cppreference.com/w/cpp/language/copy_constructor) — Richard Critten, Sep 12 '21 at 11:39
@RichardCritten, The second parameter of `Complex(Complex&, string);` has a default value, which could be a Copy Constructor. — Ghasem Ramezani, Sep 12 '21 at 11:43
@GhasemRamezani but the 1st parameter is a non-const reference - this is also unusual as it can't bind to a temporary. As a teaching/learning practice this is bad code. — Richard Critten, Sep 12 '21 at 11:45
@RichardCritten, `X::X` is a copy constructor if it's first parameter is of type `X&`, `X const&`, `X volatile&` or `X const volatile&`. https://eel.is/c++draft/class.copy.ctor — Ghasem Ramezani, Sep 12 '21 at 11:47
@GhasemRamezani agreed - but any other than `X const&` should not really be in a exercise introducing the copy constructor as how the other forms should be used is much more advanced. — Richard Critten, Sep 12 '21 at 11:48

Ghasem Ramezani · Accepted Answer · 2021-09-12T12:16:06.543

You will take a copy of Complex object on those functions:

Calculator::SumRealComp(Complex, Complex);
Calculator::SumImgComp(Complex, Complex);

So, on every call to those functions, you take two copies of the Complex object. You could pass a Complex const& object to avoid copy:

Calculator::SumRealComp(Complex const&, Complex const&);
Calculator::SumImgComp(Complex const&, Complex const&);

Copy Constructor

A copy constructor is one of the Class Special Member Functions, And called whenever we try to take a copy of the object:

class X;
void f(X); 

X x;
f(x); // <--- Here

X another(x); // <--- Here
X yet_another = x; // <--- And here

In the commented sections we could call the X copy constructor. A copy constructor could be defined as the following signatures:

X::X(X&);
X::X(X const&);
X::X(X volatile&);
X::X(X const volatile&);

Note: Like your code, we could add additional parameters to the copy constructor while they have a default value).
Note: For more information: Read Chapter 17 of "The C++ Programming Language" by Bjarne Stroustrup.

_{This is not related to your question and are my suggestions to your code, If you don't like it you could skipped(or edit it and remove it)}

Some Code Review Suggestions:

Stop using using namespace std; which could cause Undefined Behavior and give you a hard debugging time: Why is "using namespace std;" considered bad practice?
Don't complicate the Copy Constructor signature if not necessary. You could rewrite the copy constructor as follow:

Complex::Complex(Complex const& obj)
    : a(obj.a)
    , b(obj.b)
    , name(obj.name)
{
    cout << "Copy Cons called!" << endl;
    PrintComp();
}

Initialize member variables using Member Initialize List.

Thanks @GhasemRamezani All your suggestions are great and helpful for me. But I am not able to understand the syntax of copy Constructor you made. Will you please clarify it? — adityanithariya, Sep 12 '21 at 12:03
I didn't understood this: : a(obj.a) , b(obj.b) , name(obj.name) — adityanithariya, Sep 12 '21 at 12:15
@AdityaSoni, Take a good [Book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) and read it, those are basics. — Ghasem Ramezani, Sep 12 '21 at 12:17

Copy Constructor called unexpectedly

1 Answers1

Copy Constructor

Some Code Review Suggestions: