CODEWITHSUNDEEP
c++memorydynamicallocation
Ramon Blanquer
Ramon Blanquer

Reputation: 454

Deep copy dynamically allocated object in C++

Hello guys I couldn't find a way build up a proper copy constructor for a dynamically allocated object. It yells that: error: no matching function for call to 'Person::(Person*&')

My testing code is this:

#include <iostream>
#include <cstring>

class Person
{
private:
    int* age;
    std::string name;
public:
    Person(std::string name_in, int age_in);
    Person(const Person& other);
    ~Person();
    void printAge();
    void printName();
};

Person::Person(std::string name_in, int age_in)
{
    std::cout << "Creating person named " << name_in << std::endl;
    name = name_in;
    age = new int;
    *age = age_in;
}
Person::Person(const Person& other)
{
    std::cout << "Copying person." << std::endl;
    age = new int;
    *age = *other.age;
    name = other.name;
}
Person::~Person()
{
    std::cout << "Freeing memory!" << std::endl;
    delete age;
}

void Person::printAge()
{
    std::cout << "The age is " << *age << std::endl;
}

void Person::printName()
{
    std::cout << "The name is " << name << std::endl;
}


int main()
{
    Person* person1 = new Person("Ramon", 19);
    person1->printAge();
    person1->printName();

    Person* person2 = new Person(person1);
    person2->printAge();
    person2->printName();

    delete person1;
    delete person2;

    return 0;
}

It seems that when person2 object is created it is just a pointer to person1, but it is not! I stated it to be a new dynamically allocated object: Person* person1 = new Person("Ramon", 19);. Any idea what could be the cause of this?

Thanks.

Upvotes: 2

Views: 4799

Answers (3)

Shaurya Chaudhuri
Shaurya Chaudhuri

Reputation: 3842

The copy constructor that has been defined is

Person(const Person& other)

This method signature accepts a reference to the object of person, so you would need to send a reference.

In the code you are sending person1 which is a pointer as assigned by the new operator .

If you want to copy an object from pointer of another object than you should be making a method like this.

Person::Person(const Person *other)
{
    std::cout << "Copying person." << std::endl;
    age = new int;
    *age = *other->age;
    name = other->name;
}

But this is not a method signature that a copy constructor generally has, and would not copy in situations like

Person p2 = person1;

Upvotes: 1

itachi
itachi

Reputation: 302

Do make sure to write your own assignment operator also. It is similar to copy constructor but in addition to deep copy of the contents it also returns a reference to the invoking object.

Upvotes: 1

barak manos
barak manos

Reputation: 30136

A copy constructor takes the input argument by reference, not by pointer.

Change this:

Person* person2 = new Person(person1);

To this:

Person* person2 = new Person(*person1);

Upvotes: 7

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