Initializing array of objects

Question

I want to initialize an array. There's no compilation error but when I run the program it shows the first cout then stop running.

Here's my code:

class A {
    string first_name ;
    string last_name;
    int ID;
public:
    virtual void print ()=0;
};

class B :public A{
    string phone_number;

    .......
    void print(){
        ........
    }
};

class D{
    A** a;
    int size;
public:
    D(){
        size = 10;
        a = new A *[size];
        for(int i = 0 ; i<size ; i++){
            a[i] = NULL;
        }
    }

    void Add(){
        for(int i = 0 ; i<size ; i++){
            A * a2 = a[i];
            B * b  = dynamic_cast<B*>(a2);
            int id;
            cout<<"enter the id";
            cin>>id
            b->set_ID(id);
            // i did the same (cout , cin statements) for the first name and last name.
            b->set_first_name();
            b->last_name();
        }
};

Is this not correct?

You mean it prints "enter the id" and then after you enter an ID it doesn't continue? — Joseph Mansfield, Dec 21 '13 at 13:57
All of the pointers in `a` are uninitialized when you initialize `a2` with them. — chris, Dec 21 '13 at 13:58
@sftrabbit Yes , i did the cout and cin for the others (first name , last name ) but it didn't show up , and the program stop running — Rai Ou, Dec 21 '13 at 13:59
You do know about [`std::vector`](http://en.cppreference.com/w/cpp/container/vector)? — Some programmer dude, Dec 21 '13 at 13:59
Please format your code properly in the future. It’s not acceptable to write code without formatting, much less post it like that on here. — Konrad Rudolph, Dec 21 '13 at 14:03

Joseph Mansfield · Accepted Answer · 2013-12-21T14:08:38.373

1

You allocate size amount of A*s, but you don't actually make those pointers point anywhere. ~~They're uninitialized.~~ Edit: now you're just setting them to NULL. You would need to allocate some A objects and assign their addresses to each of the elements of a. However, I see no good reason for you to be dynamically allocating the array of pointers - why don't you just declare a as A* a[10];? (or better yet, use a std::vector or std::array)

edited Dec 21 '13 at 14:08

answered Dec 21 '13 at 14:01

Joseph Mansfield

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I use the dynamically allocating because of the phone_number , i couldn't reach it without dynamically allocating ! – Rai Ou Dec 21 '13 at 14:03
2

@RaiOu It looks more like you use dynamic allocation because you don't know how to use standard library containers. – juanchopanza Dec 21 '13 at 14:05
2

Just a side remark : he never deallocate his `A` objects. That's a problem when allocating objects, it's easy to forget to deallocate them. – Gabriel L. Dec 21 '13 at 14:10
1

@GabrielL. that would lead to undefined behaviour, because `A` has no virtual destructor :-) – juanchopanza Dec 21 '13 at 14:16

Initializing array of objects

1 Answers1