Re: std::vector question

From:

francis.glassborow@btinternet.com (Francis Glassborow)

Newsgroups:

comp.std.c++

Date:

Mon, 26 Nov 2007 19:36:48 GMT

Message-ID:

<OsOdnf5_z6QhgNbanZ2dnUVZ8s-qnZ2d@eclipse.net.uk>

Tomer wrote:

Hi,
I have the following scenario:

class A {};

class B : public A {};

void TestingA(std::vector<A*> Tesing) {}

main()
{
  std::vector<B*> Bs;
  TestingA(Bs);
}

On VC++ 2008 I get the following error:
error C2664: 'TestingA' : cannot convert parameter 1 from
'std::vector<_Ty>' to 'std::vector<_Ty>'
        with
        [
            _Ty=B *
        ]
        and
        [
            _Ty=A *
        ]
        No user-defined-conversion operator available that can perform
this conversion, or the operator cannot be called

Can you please explain?

There is no relationship between a container of A* and a container of B*
even though there is a relationship between A and B. IIRC this is not
limited to the pointer case, there are no builtin conversions between
template specialisations for different types regardless of the types
regardless of any conversions (user defined or implicit) between the types.

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