Re: [Boost-Users] Re: [boost] Iterator Adaptor Poll

From: David Abrahams (dave_at_[hidden])
Date: 2002-07-26 11:54:10

-----------------------------------------------------------
           David Abrahams * Boost Consulting
dave_at_[hidden] * http://www.boost-consulting.com

----- Original Message -----
From: "Jeremy Siek" <jsiek_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Friday, July 26, 2002 12:16 PM
Subject: Re: [Boost-Users] Re: [boost] Iterator Adaptor Poll

> On Fri, 26 Jul 2002, David Abrahams wrote:
> dave>
> dave> Thanks! Now where's that line_iterator?
> dave>
>
> Right here :)

Do you think this makes a good "hello, world"?

It stores state in the Policies object, and returns an internal reference.
Both of these features make it a bit too complicated for a very basic
introduction, IMO.

-Dave

> // Example adapted from page 4 of Matthew Austern's
> // "Generic Programming and the STL".
>
> #include <iostream>
> #include <string>
> #include <cassert>
> #include <boost/iterator_adaptors.hpp>
> #include <boost/cstdlib.hpp>
>
> class line_iterator_policies : public boost::default_iterator_policies
> {
>   std::istream* in; // rationale for pointer: if we did
> reference
> // instead, then iterator could not be
> default
> // constructible.
>   std::string line;
> public:
>   line_iterator_policies() : in(0) { } // always need a default
> constructor
>   line_iterator_policies(std::istream& in) : in(&in) { }
>
>   void initialize(bool& at_end) {
>     if (in != 0)
>       read(at_end);
>     else
>       at_end = true;
>   }
>
>   template <typename IteratorAdaptor>
>   typename IteratorAdaptor::reference
>   dereference(const IteratorAdaptor& x) const
>     { return line; }
>
>   template <typename IteratorAdaptor>
>   void increment(IteratorAdaptor& x) { read(x.base()); }
> private:
>   void read(bool& at_end) { assert(in != 0);
>     if (*in)
>       std::getline(*in, line);
>     if (*in)
>       at_end = true;
>     else
>       at_end = false;
>   }
> };
>
>
> typedef boost::iterator_adaptor<bool, // for at_end
>   line_iterator_policies,
>   boost::value_type_is<std::string>,
>   boost::reference_is<std::string>,
>   boost::pointer_is<std::string*>,
>   boost::difference_type_is<std::ptrdiff_t>,
>   boost::iterator_category_is<std::input_iterator_tag>
> > line_iterator;
>
> line_iterator make_line_iterator(std::istream& in) {
>   bool at_end;
>   line_iterator_policies p(in);
>   return line_iterator(at_end, p);
> }
>
> int main()
> {
>   line_iterator iter = make_line_iterator(std::cin), eof_iter;
>   std::vector<std::string> vec(iter, eof_iter);
>   std::sort(vec.begin(), vec.end());
>   std::copy(vec.begin(), vec.end(),
>     std::ostream_iterator<std::string>(std::cout, "\n"));
>   return boost::exit_success;
> };
>
>
>
> ----------------------------------------------------------------------
>  Jeremy Siek                          http://php.indiana.edu/~jsiek/
>  Ph.D. Student, Indiana Univ. B'ton   email: jsiek_at_[hidden]
>  C++ Booster (http://www.boost.org)   office phone: [phone]
> ----------------------------------------------------------------------
>
>
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