Dynamically allocated array of an abstract type

How can you ynamically allocate an array of an abstract type?
eg.

Code:

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    int i; Abstract* a;
    cout << "How many ? ";
    cin >> i;
   
    a = new (nothrow) Abstract[i];

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Class Abstract is abstract(has a = 0 function) and has 2 non-asbtract child classes(which I want to use to fill the array).
However if I hardcode the array it works
eg.

Code:

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    Abstract* a[] = {
        new ConcreteOne(),
        new ConcreteTwo(),
        new ConcreteOne()
    };

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The first is an array of Abstract objects, which is invalid.
The second is an array of pointers to Abstract, which is valid.

Code:

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Abstract** a = new Abstract*[i];

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Remember to delete both every individual object, and then array. A Boost.PtrContainer would make this stuff a lot easier.

Whooh that was fast.
Thanks.
I've just started with C++ so I don't know much about the different libs, but I'll take a look at that Boost library.

If you just started with C++ (or even if you haven't) you shouldn't be using new to create a dynamic array. Use vector instead. Or in this case, the boost ptr_vector because you are holding pointers in your array.

Quote:

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Originally Posted by Zerok

Whooh that was fast.
Thanks.
I've just started with C++ so I don't know much about the different libs, but I'll take a look at that Boost library.

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just to give you fair warning, the boost library is HUGE. try not to be intimidated by it.