Initialize Constructor when its an array

[stephenalistoun]

Hi all,

How do you initialize a class constructor when its an array?

I'm struggling with the stuff in bold.

class PhoneCall{
private:
    string number;
    float rate;
    int length;
public:
    PhoneCall();
    PhoneCall(string initNumber , int initLength , float initRate);
};

int main(){
   PhoneCall phoneCallDirectory[100];
   
   int count = 0;
   for(int i = 0; i < 100;i++){
     phoneCallDirectory[count]->PhoneCall("" , 0 , 0);
     count++;
   }
}

Thanks,

Stephen

[kooth]

What seems to be the problem?

[Galik]

With an array the elements are initialized using the default constructor. So you can't use arguments.

[stephenalistoun]

So are you saying the only way to fix the problem is to use property accessors

[Galik]

Yes.

[Galik]

Well, for your example you can simply define a default constructor:

PhoneCall::PhoneCall()
: rate(0.0f)
, length(0)
{
}

That constructor will be called for every element of the array when you create it.

[webJose]

It might be possible. See http://www.cplusplus.com/reference/std/new/operator%20new/. The third form allows the selection of the constructor. In the example, see lines 18 to 25.

But so we are clear: Your current approach of an array in the stack does not allow the selection of the constructor. The previous answers are truly correct. I am saying: Instead of an array in the stack, dynamically create one in the heap and construct the objects with operator new.

[ne555]

Instead of trying to emulate a vector, just use it http://www.cplusplus.com/reference/stl/vector/

However phoneCallDirectory[count]->PhoneCall("" , 0 , 0); what do you want to do there?
phoneCallDirectory[count] is an object, you access its fields with the dot operator.
If you want to set it to that value, maybe it is a work for the default constructor
Or phoneCallDirectory[count] = PhoneCall("" , 0 , 0);

[webJose]

+1 to the vector, but note that this is not exactly the same, or maybe I don't know how to use the vector.

The vector will use the copy constructor and the user wants to use some other constructor. If I dynamically create the vector myself, my performance will be better than if I used vector, right?

[ne555]

I thought that the copy constructor could be bypassed. I mean if the object will be destroyed next, something like RVO could be used.
http://en.wikipedia.org/wiki/Return_value_optimization

There is also the alternative of storing pointers instead (but that is awful).

Other than that I don't know how you could avoid the copy constructor.

[webJose]

I think the copy ctor is not bypassed in vector<>. :-( I recently read a PPT about custom allocators for use with STL containers and apparently all containers push the item using the copy constructor. The memory allocator objects even have a construct() method that uses the placement new operator to place the copy in the allocated memory.