CODEWITHSUNDEEP
c++pointersconstructorcopy
Andrei Florea
Andrei Florea

Reputation: 3

Copy constructor for pointers to object

I'm kind of new in C++ classes and I need to make a copy constructor that uses pointers to object. My class looks like this:

class test
{
    int a;
    char *b;
public:
    test()
    {
        a=0;
        b="\0";
    }
    test(const test &p)
    {
        b=new char(strlen(p.b)+1);
        b=p.b;
        a=p.a;
        cout<<"The copy constructor works";
    }
    void seta(int nr)
    {
        a=nr;
    }
    void setb(char *s)
    {
        b=s;
    }
    int geta()
    {
        return a;
    }
    char *getb()
    {
        return b;
    }
};

Now I have a pointer to an object

 test *x;
 x=new test;

What I need to do is to create another pointer to object,*y,that will have the same values as x,using the copy constructor. If they were objects and not pointers,that copy constructor would have worked. Can you tell me what I should do,please? Thanks!

Upvotes: 0

Views: 85

Answers (2)

Captain Obvlious
Captain Obvlious

Reputation: 20063

Simple, just dereference x when you pass it to the constructor of test.

test* y = new test(*x);

Upvotes: 0

Mike Seymour
Mike Seymour

Reputation: 254431

What you should probably do is not use pointers.

If you really want to do this, you can combine new with a copy-constructor thusly:

test *y = new test(*x);

You also need to fix your copy constructor to copy the contents of the string, not the pointer:

strcpy(b, p.b);  // not b = p.b;

and fix the default constructor so it doesn't point to a string literal (which will fail to compile on a modern compiler, and will go horribly wrong if you ever try to add a destructor to fix the memory leak).

If you're new to C++, you might have more fun using basic types, and friendly library types like std::string, before facing the insanity of pointers and memory allocation.

Upvotes: 2

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