how to initialize object of class with two pointers?

Question

Ok, so i know this is kind of basic, but i can't understand what i'm doing wrong here. this is the class:

class numar_complex {
    friend std::ostream& operator<<(std::ostream& out, const numar_complex& numar_complex);
    friend std::istream& operator>>(std::istream& is, numar_complex& numar_complex);

private:
    double* p_real;
    double* p_imaginar;

public:
    //constructor, destructor:
    numar_complex()
    {

        double* p_real{ new double(0.0) };

        double* p_imaginar{ new double(0.0) };

        cout << "constructor" << endl;
    }
    numar_complex(const numar_complex& nr)
    {
        if (p_real != nullptr) {
            p_real = nullptr;
            delete p_real;
        }
        p_real = new double(*nr.p_real);
        if (p_imaginar != nullptr) {
            p_imaginar = nullptr;
            delete p_imaginar;
        }
        p_imaginar = new double(*nr.p_imaginar);
        cout << "copy constructor " << endl;
    }
    ~numar_complex()
    {
        p_real = nullptr;
        delete p_real;
        p_imaginar = nullptr;

        delete p_imaginar;

        cout << "destructor" << endl;
    }

    // getteri:

    double get_p_real()
    {
        return *p_real;
    }
    double get_p_imaginar()
    {
        return *p_imaginar;
    }
    //setteri:

    void set_p_real(double x)
    {
        p_real = nullptr;
        delete p_real;
        p_real = new double(x);
    }
    void set_p_imaginar(double x)
    {
        p_imaginar = nullptr;
        delete p_imaginar;
        p_imaginar = new double(x);
    }
    std::ostream& operator<<(std::ostream& out, const numar_complex& numar_complex)
    {
        if (*numar_complex.p_imaginar >= 0) {
            out << *numar_complex.p_real << "+" << *numar_complex.p_imaginar << "*i \n";
        }
        else if (*numar_complex.p_imaginar < 0) {
            out << *numar_complex.p_real << *numar_complex.p_imaginar << "*i \n";
        }

        return out;
    }

and for some reason, when i simply declare an object of this class, as

numar complex x; 
cout << x;

it crashes (memory problem); however, if i use the setters/getters, the problem doesn't appear anymore. in the case of

numar complex x; 
x.set_p_real(1); 
x.set_p_imaginar(1); 
cout << x;

will result in 1 + 1i;
PS: If i don't use the setters to initialize values, the getters will also result in a crash.

This doesn't answer your question, but perhaps consider using std::complex? Or at least another library class? — J...
– J..., Commented Aug 25, 2021 at 10:37
In your constructor, you create local variables, which are discarded as soon as constructor finishes. Member variables are not initialized by this constructor. — Yksisarvinen
– Yksisarvinen, Commented Aug 25, 2021 at 10:38
You need to call delete on a pointer, THEN set it to nullptr. — Bas in het Veld
– Bas in het Veld, Commented Aug 25, 2021 at 10:40
There's nothing in the shown code that requires the use of pointers. It only makes the shown code twice as bigger, and more bug prone, than it needs to be. By replacing the pointers with plain doubles the shown code will be half its current size. No need to have a copy constructor. No need to have an assignment operator (one was missing). No opportunities for making simple bugs, like attempting to delete a null pointer. This kind of a bug is called "pointless use of pointers". — Sam Varshavchik
– Sam Varshavchik, Commented Aug 25, 2021 at 10:45

Karen Baghdasaryan · Accepted Answer · 2021-08-25 11:20:59Z

2

In the constructor you don't initialize p_real and p_imaginar, you declare new variables, which only live within the scope of constructor, and hence get destroyed, resulting in memory leak.

To avoid this I recommend using member initializer lists

class complex
{
private:
    double* p_real;
    double* p_imaginar;

public:
    numar_complex():
       p_real(new double(0.0)),
       p_imaginar(new double(0.0))
    {
        cout << "constructor" << endl;
    }

    .
    .
    .
    .
    //the rest
}

answered Aug 25, 2021 at 11:20

Karen Baghdasaryan

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