Question

How to intialize array in Constructor initializer list?

Asked by: naseeam

An object in Constructor initializer list is intialized as follows:

x(2, 3, 5),

x is a private member of  class1.  x is object of type class2.  class2 has 3 private
members, which are intialized in above constructor to 2, 3, 5.

What if x was array of objects.  How would the initalizer list look then?

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Asked On
2009-11-03 at 15:32:37ID24869332
Topic

C++ Programming Language

Participating Experts
4
Points
500
Comments
7

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Answers

 

by: jkrPosted on 2009-11-03 at 16:03:02ID: 25735248

If x was used as an array, e.g.

x* p = new x[42];

all you can use is the default constructor. No others are possible.

 

by: evilrixPosted on 2009-11-03 at 23:46:35ID: 25737196

>> How to intialize array in Constructor initializer list?
You can't, it's not possible to initialise a member array in a constructor initialisation list. You have to do this in the constructor itself.

 

by: Let_Me_BePosted on 2009-11-04 at 00:20:37ID: 25737333

Actually.

#include <new>
#include <cstdlib>
using namespace std; 
struct SomeStuff
{ SomeStuff(int) {} }; 
int main()
{
  SomeStuff *arr = (SomeStuff*)malloc(sizeof(SomeStuff)*10);
  for (int i = 0; i < 10; i++)
    new(&arr[i]) SomeStuff(i); 
  for (int i = 0; i < 10; i++)
    arr[i].~SomeStuff(); 
  free(arr);
}
                                              
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by: evilrixPosted on 2009-11-04 at 00:41:25ID: 25737421

>> Actually.
Actually what?

 

by: Infinity08Posted on 2009-11-04 at 01:05:55ID: 25737543

You could always use a vector instead of an array :

class Foo {
  private :
    std::vector<int> _vec; 
  public :
    Foo(const std::vector<int> &vec) : _vec(vec) { }
}; 

std::vector<int> vec;
// fill the vector ...
Foo foo(vec);

                                              
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by: Let_Me_BePosted on 2009-11-04 at 01:09:37ID: 25737554

> Actually what?

Actually it can be done (It was not reaction on your comment), but not in the initializer list.

 

by: evilrixPosted on 2009-11-04 at 01:20:46ID: 25737593

>> Actually it can be done
I mean you should post an explanation with your code example... since not everyone will know what placement new is or how to use it.

Placement new can be tricky to use safely, more so than your simple example eludes. It's very easy to write code that can leak (amongst other potential issues).

naseeam, if you decide to consider LMB's idea I suggest you take a look at these first.

http://www.parashift.com/c++-faq-lite/dtors.html#faq-11.14
http://www.parashift.com/c++-faq-lite/dtors.html#faq-11.10

-Rx.

20120131-EE-VQP-002

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