Re: Why no std::back_insert_iterator::value_type?

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

23 Nov 2006 07:04:43 -0500

Message-ID:

<bBe9h.53400$uv5.357759@twister1.libero.it>

Terry G ha scritto:

Sorry, I've been guilty of that on several posts recently. I'm in a hurry.
Here's some runnable code that illustrates my point.
It contains my previous code, that used a vector<MyType>, where MyType is
uint8_t.
I wanted to allow the user to use the container of her choice and a
reasonable type too.
Thats the "current" version.
Then, I show the code that I wish would work, but it doesn't because
value_type for back_inserter is void.

<code snipped>>

Much better! ;-)

Maybe this could be a solution:

template <class T>
struct true_value_type
{
    typedef typename std::iterator_traits<T>::value_type type;
};

template <class T>
struct true_value_type<std::back_insert_iterator<T> >
{
    typedef typename T::value_type type;
};

then you just use

template <class OutIter>
OutIter CopyOutWish(OutIter dst, const uint8_t* src, size_t size,
          unsigned count)
{
   typedef typename true_value_type<OutIter>::type DstType;
   /* */
}

HTH,

Ganesh

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