Valarray/Pointer to first Element

Hello Group,
>
there is some memberfunc for std::valarray to return a pointer to the
first element in the array. How do i use this? Thanx a lot.
>
HAND Chris

Hello Group,
>
there is some memberfunc for std::valarray to return a pointer to the
first element in the array. How do i use this? Thanx a lot.

On Nov 2, 10:43 am, Chris Forone <4...@gmx.atwrote:>
Correct me if I am wrong, but I don't believe any std container has
methods to give you a pointer to any of thier contents, and rightly
so. You can get a reference to it.

Why would you want a pointer to the
first element?

What type are you assuming its elements are?

How would
you use it opposed to a reference?

On 2007-11-02 16:43, Chris Forone wrote:>
&val[0];
>
Where val is a valarray.
>
>

Erik Wikström schrieb:This solution i have already. I have seen on a Website:
>
valarray::operator T *
>
operator T *();
operator const T *() const;
>
Both member functions return a pointer to the first element of the
controlled array, which must have at least one element.
>
But i dont know, how to apply this operator...

On 2007-11-02 17:35, Chris Forone wrote:>
Use static_cast:
>
double* p = static_cast<double*>(val);
>
where val is a valarray of doubles with at least one element.
>

Christopher wrote:

you can get the address of all the elements.

why not? For example, to apply the std library algorithms. A
pointer to an element of a valarray is a random-access
iterator.

Erik Wikström schrieb:On 2007-11-02 16:43, Chris Forone wrote:

This solution i have already. I have seen on a Website:

valarray::operator T *

operator T *();
operator const T *() const;

Both member functions return a pointer to the first element of
the controlled array, which must have at least one element.

On Nov 2, 5:35 pm, Chris Forone <4...@gmx.atwrote:>>>>>>
Which Web site? It's not in the standard. In general, the
authors of the standard avoided implicit conversions.
Correctly---there are really very few cases where they dont'
cause problems.

>>
Neither member function exists.
>
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orientée objet/
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>

On Nov 2, 5:27 pm, Zeppe <ze...@remove.all.this.long.comment.yahoo.it>
wrote:>>>
You're wrong, of course. If you can get a reference, you can
get a pointer.
>>
Of any of the elements. (At least, I think that's what you
mean; "all of the elements" is ambiguous, and can mean two
different things.)
>>>
I think that valarray is guaranteed to be continuous. As is
std::vector, and (soon) std::basic_string. That's not true for
other containers, however, and a pointer to a given element is
not generally a random-access iterator into the container.
(Again, I think you know this, and were only refering to
valarray, but it's not clear.)
>
The most frequent need for a pointer is, of course, interfacing
with legacy code or with C. In which case, the type of the
container is constrained; if the C code expects a pointer to the
first element, you can use vector, I think valarray, and in
practice basic_string, but nothing else.
>
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
>