On 9/28/05, <b class="gmail_sendername">David Abrahams</b> &lt;<a href="mailto:dave@boost-consulting.com">dave@boost-consulting.com</a>&gt; wrote:<div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>:) Yes, that's expected.&nbsp;&nbsp;When dereferenced, indirect_iterator gives<br>you a reference onto an existing value.<br><br>&gt; Why isn't this working?<br><br>It wasn't designed to do that.</blockquote><div><br>
&nbsp;But it is possible to do input with an indirect_iterator no? I mean, there's the example from the <br>
documentation (somewhat summarized):<br>
<br>
&nbsp;&nbsp; char*
pointers_to_chars[N];&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<br>
&nbsp;&nbsp; char* pointers_to_mutable_chars[N];<br>
<br>
&nbsp;&nbsp; boost::indirect_iterator&lt;char* const*&gt; mutable_indirect_first(pointers_to_mutable_chars), <br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mutable_indirect_last(pointers_to_mutable_chars + N);<br>
&nbsp;&nbsp; boost::indirect_iterator&lt;char* const*, char const&gt; const_indirect_first(pointers_to_chars),&nbsp; <br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
const_indirect_last(pointers_to_chars + N);<br>
<br>
&nbsp; std::transform(const_indirect_first, const_indirect_last,
mutable_indirect_first, std::bind1st(std::plus&lt;char&gt;(), 1));<br>
<br>
There you do use mutable_indirect_first to copy data into an array of pointers. Ok, my approach using the<br>
helper function was most likely too naive, though I'm not entirely sure why that one doesn't work. <br>
&nbsp;I tried doing the same with a vector of smartpointers, but I can't get that to work. I don't really get how to do the <br>
&quot;char * const *&quot; equivalent, substituting &quot;const iterator&lt;shared_ptr...&gt;&quot; doesn't compile. Making it non-const compiles,<br>
but crashes. This is the code:<br>
<br>
&nbsp;&nbsp;&nbsp; typedef boost::shared_ptr&lt; double &gt; d_ptr;<br>
&nbsp; &nbsp; typedef std::vector&lt; d_ptr &gt;::iterator const d_it;<br>
<br>
&nbsp;&nbsp;&nbsp; std::vector&lt; d_ptr &gt; v( 10 );  <br>
&nbsp;&nbsp;&nbsp; std::vector&lt; d_ptr &gt; w( 10 );<br>
&nbsp;&nbsp;&nbsp; <br>
&nbsp;&nbsp;&nbsp; boost::indirect_iterator&lt; d_it &gt; mutable_indirect_first( w.begin() ), <br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mutable_indirect_last( w.end() );<br>
&nbsp;&nbsp;&nbsp; boost::indirect_iterator&lt; d_it, double const&gt; const_indirect_first( v.begin() ), <br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
const_indirect_last( v.end() );<br>
&nbsp;&nbsp;&nbsp; std::copy( c_indirect_first, c_indirect_last, mut_indirect_first );&nbsp; <br>
<br>
And this is the error message:<br>
<br>
&nbsp;/usr/include/boost/shared_ptr.hpp:247: typename
boost::detail::shared_ptr_traits&lt;T&gt;::reference
boost::shared_ptr&lt;T&gt;::operator*() const <br>
&nbsp;[with T =&nbsp;&nbsp;&nbsp; double]: Assertion `px != 0' failed.<br>
<br>
&nbsp;I must say it's all a bit beyond me right now. Could you explain why things go wrong here?<br>
</div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">&gt; Also, some way to get it to work as a back_insert_iterator would be<br>&gt; interesting, does this exist (aside from writing your own)?
<br><br>Neither exists, but for either one, writing your own is possible using<br>iterator_facade.&nbsp;&nbsp;The tutorial is at<br><a href="http://www.boost.org/libs/iterator/doc/iterator_facade.html#tutorial-example">http://www.boost.org/libs/iterator/doc/iterator_facade.html#tutorial-example
</a></blockquote><div><br>
&nbsp;Ok, I'll look into it, thanks.<br>
&nbsp;</div></div>-- <br>Alex Borghgraef