Calling parameterized constructor while creating array of objects in heap

Asked Apr 19 '20 at 07:59

Active Apr 19 '20 at 08:54

Viewed 92 times

class A{
    int a;
public:
    A(int i){
        a=i;
    }
};


class B{
    int b;
    A *arrA;
public:
    B(int n){
        b=n;
        arrA=new A[n];
    }
};

Now, I want to send 'n' to the constructor of all objects of A being created using 'new' in B. How can I do it?

edited Apr 19 '20 at 08:54

Jarod42

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asked Apr 19 '20 at 07:59

letsShareKnowledge

This help you out: [Object array initialization without default constructor](https://stackoverflow.com/questions/4754763/object-array-initialization-without-default-constructor)? – user4581301 Apr 19 '20 at 08:03
you can use `std::vector` – 463035818_is_not_an_ai Apr 19 '20 at 08:17
`vector` would set all of the elements to the same value unless you do some really spooky stuff. – user4581301 Apr 19 '20 at 08:44
@idclev463035818 if there is any way without using vector? – letsShareKnowledge Apr 19 '20 at 08:49
@user4581301 OP wants to pass the same `n` to all elements constructors – 463035818_is_not_an_ai Apr 19 '20 at 08:50
why don't you want to use `std::vector`? – 463035818_is_not_an_ai Apr 19 '20 at 08:50
`std::vector` does correctly manage the dynamic memory, your class does not ;) – 463035818_is_not_an_ai Apr 19 '20 at 08:51
@idclev463035818 Ja. I misread the code. Somehow my brain put in extra garbage. – user4581301 Apr 19 '20 at 08:54
@letsShareKnowlede you would have to use [placement `new`](https://en.cppreference.com/w/cpp/language/new#Placement_new), and that's somewhere you do not want to go without a very good reason and a fair amount of experience with C++. I think one of the answers in the link I dropped into the first comment covers it. Use the `vector` though. The pain level will be several orders of magnitude lower. – user4581301 Apr 19 '20 at 08:57
@user4581301 I want to do it once without using vector and the answers in the link don't really clear it for me. Maybe I am unable to get them. – letsShareKnowledge Apr 19 '20 at 09:04
@idclev463035818 If it can be done without using vector? – letsShareKnowledge Apr 19 '20 at 09:07
@letsShareKnowlede It cannot be done without reimplementing the features of `std::vector` that would allow you to do it or similar. Why don't you want to use `std::vector` ? – 463035818_is_not_an_ai Apr 19 '20 at 09:10
The placement `new` example in the second answer is about as simple as they come, unfortunately. Can it be done without `vector`? Yes, but you'll find you pretty much rewrote `vector`. – user4581301 Apr 19 '20 at 09:12

Calling parameterized constructor while creating array of objects in heap

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