Re: C++/CLI - How to convert List<T> to vector<T>

From:

Victor Bazarov <v.Abazarov@comAcast.net>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 28 Sep 2009 13:03:51 -0400

Message-ID:

<h9qq9s$k8a$1@news.datemas.de>

Ben Voigt [C++ MVP] wrote:

"JohnR" <_no_spam@_no_spam.com> wrote in message
news:#1hpNBEQKHA.1268@TK2MSFTNGP04.phx.gbl...

Hi there,

I'm new to C++/CLI but very experierced in both C++ and .NET. Can
someone show me the basic syntax for converting a List<T> to vector<T>
(or more generally, any .NET generic to its C++ template equivalent).
For now I'm looking for a template with a signature similar to the
following (note however that "T" would also need to be converted
presumably so a template arg and a generic arg may be required).
Thanks in advance.

std::vector<T> marshal_as(System::Collections::Generic::List<T> ^
const & list)

Returning vector by value is going to have really bad performance unless
you have the move optimization.

For types which have dual managed/native identity (i.e. built-in numeric
types), something like:

template<typename T>
std::vector<T> marshal_as(System::Collections::Generic::ICollection<T>^
list)
{
   if (list == nullptr) throw gcnew ArgumentNullException(L"list");
   std::vector<T> result(list->Count);
   for each (T& elem in list)
       result.push_back(elem);

That's A BAD IDEA(tm). You're going to end up with the vector that has
its first list->Count elements default-initialized and the actual
meaningful elements that follow (and total of list->Count*2 elements).
Perhaps you meant

     std::vector<T> result;
     result.reserve(list->Count);
     for each (...

Or maybe you meant

     std::vector<T> result(list->Count);
     for (int i = 0; ...
         result[i] = list->??? ; // or use iterators

   return result;
}

More generally, something like:

template<typename T>
generic<typename S>
std::vector<T> marshal_as(System::Collections::Generic::ICollection<S>^
list)
{
   if (list == nullptr) throw gcnew ArgumentNullException(L"list");
   std::vector<T> result(list->Count);
   for each (S& elem in list)
       result.push_back(marshal_as<T>(elem));

Same notes as above.

return result;
}

Not compile-tested.

V
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