How to make a dynamically allocated array that can hold derived objects in c++

Question

Hello I'm doing a project for school that must use a dynamically allocated array of objects. I'm wondering where I went wrong on this one.

Mammal* Pets = new Mammal[arraysize]; Pets[count] = new Dog(tempweight, tempname)

There is an error that says no operator matches these operands for the second line of code.

Here is my constructor if that helps, and the Dog constructor.

Mammal::Mammal(void)
{
weight = 0;
name = "";
cout << "Invoking Mammal Default Constructor\n";
}

Mammal::Mammal(int tempweight, string tempname)
{
weight = tempweight;
name = tempname;
cout << "Invoking Mammal Constructor\n";
}

Dog::Dog(int tempweight, string tempname)
{
Setweight(tempweight);
Setname(tempname);
cout << "Invoking Dog Constructor\n";
}

Thank you,

glampert · Accepted Answer · 2014-04-24 01:29:40Z

3

You need to declare an array of pointers, like so:

Mammal ** Pets = new Mammal*[arraysize];

answered Apr 24, 2014 at 1:29

glampert

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user2848971 · Accepted Answer · 2014-04-24 01:31:24Z

3

You're trying to set a Dog* to a Mammal object. You have a pointer of Mammal objects. In this case you'll actually want an array of pointer to Mammal objects.

But don't do that. Use an std::vector of Mammal* at least:

std::vector<Mammal*> pets;

Or if you know the size and don't need to change it:

std::array<Mammal*, 10> pets;

Even better still:

std::vector<std::unique_ptr<Mammal>> pets;

answered Apr 24, 2014 at 1:31

user2848971

7 Comments

Qaz Over a year ago

And by at least, you of course mean a vector of smart pointers :)

user2848971 Over a year ago

Yeah, that'd be the best way to go about it.

Brett Holmes Over a year ago

I would use vector, but I don't exactly know how to do that in this class so I think it'd be best to go with glampert's code. Thanks though!

user2848971 Over a year ago

@BrettHolmes Not knowing how to use a language feature / library is an excuse to write bad code?

Qaz Over a year ago

@BrettHolmes, For the most part, you can use these the exact same way as an array or pointer apart from the declaration, but no need to clean up, and no need to worry about an exception happening and causing a lack of cleanup.

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