Re: vector of structs?

"Igor Tandetnik" <>
Thu, 27 Apr 2006 16:43:38 -0400
Jason S <> wrote:

If I have

typedef struct {
 short s;
 MyClass obj;
 CComPtr<something> p;
} X_t;

should I use vector<X_t> or vector<X_t*>?

Either, assuming MyClass has an appropriate copy constructor and
assignment operator. Personally, I prefer vector of values to vector of
pointers whenever possible.

If the former, how do I
handle push_back() with a structure?

The same way you do it with a pointer or a simple type. What exactly
seems to be the problem?

If the latter, then don't I have
to allocate memory for X_t

You do.

in which case, what's the point of using

You don't have to manage the collection: grow and shrink the underlying
buffer as needed, keep track of the number of elements.

And if I do choose to allocate memory for X_t, I can't just
use malloc/CoTaskMemAlloc(sizeof(X_t)*N), because then how will it
properly initialize the non-simple types contained in X_t like obj()
and p() which might have constructors?

What's wrong with

new X_t();

? You need to allocate memory for each element indvidually, not for all
of them at once, so I'm not sure where sizeof(X_t)*N comes from.

The main problem with vector<X_t*> is not that you need to allocate
memory for each X_t element, but that you need to free it at some point.
The vector won't do it for you. So every time you remove an element from
the vector you would have to manually delete it - a breeding ground for
memory leaks. Smart pointers like boost::shared_ptr can help here.
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

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