| Topic: |
DEVELOP > c-Plus-Plus |
| User: |
"Jess" |
| Date: |
28 Jun 2007 09:30:55 AM |
| Object: |
help on std::iterator_traits? |
Hello,
I read a document that says iterator_traits is contains only nested
definitions. It seems to have definitions like value_type, reference
etc. If I define my own container, I can define these types without
iterator_traits. Therefore, could somebody please tell me why we need
to use iterator_traits at all?
Thanks a lot!
Jess
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| User: "Kai-Uwe Bux" |
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| Title: Re: help on std::iterator_traits? |
28 Jun 2007 09:58:05 AM |
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Jess wrote:
Hello,
I read a document that says iterator_traits is contains only nested
definitions. It seems to have definitions like value_type, reference
etc. If I define my own container,
You probably mean "iterator" instead of "container"
I can define these types without
iterator_traits. Therefore, could somebody please tell me why we need
to use iterator_traits at all?
The iterator_traits are the interface for algorithms to know about the
iterators passed. Note that T* is supposed to be a valid iterator. Yet,
there is no such thing as (T*)::value_type. However, iterator_traits<T*> is
specialized in the expected way. This is another case of a problem being
solved by introducing "yet another level of indirection"(tm).
Best
Kai-Uwe Bux
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| User: "Zeppe" |
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| Title: Re: help on std::iterator_traits? |
28 Jun 2007 10:01:12 AM |
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Jess wrote:
Hello,
I read a document that says iterator_traits is contains only nested
definitions. It seems to have definitions like value_type, reference
etc. If I define my own container, I can define these types without
iterator_traits. Therefore, could somebody please tell me why we need
to use iterator_traits at all?
Because the algorithms that rely on the iterators don't really care
about your container. If you write a container, and write your own
iterator for it, an algorithm that performs some operation on your data
can be written as:
template <class It>
void foo(It begin, It end){
iterator_traits<It>::value_type v;
// bla bla bla...
}
it's an elegant way to group all the information that depends on the
iterator.
Regards,
Zeppe
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| User: "Victor Bazarov" |
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| Title: Re: help on std::iterator_traits? |
28 Jun 2007 09:55:30 AM |
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Jess wrote:
I read a document that says iterator_traits is contains only nested
definitions. It seems to have definitions like value_type, reference
etc. If I define my own container, I can define these types without
iterator_traits. Therefore, could somebody please tell me why we need
to use iterator_traits at all?
You don't.
V
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