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< title > Indirect Iterator< / title >
< meta name = "author" content = "David Abrahams, Jeremy Siek, Thomas Witt" / >
< meta name = "organization" content = "Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" / >
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< meta name = "date" content = "2004-01-12" / >
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< meta name = "copyright" content = "Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved" / >
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< body >
< div class = "document" id = "indirect-iterator" >
< h1 class = "title" > Indirect Iterator< / h1 >
< table class = "docinfo" frame = "void" rules = "none" >
< col class = "docinfo-name" / >
< col class = "docinfo-content" / >
< tbody valign = "top" >
< tr > < th class = "docinfo-name" > Author:< / th >
< td > David Abrahams, Jeremy Siek, Thomas Witt< / td > < / tr >
< tr > < th class = "docinfo-name" > Contact:< / th >
< td > < a class = "first reference" href = "mailto:dave@boost-consulting.com" > dave@ boost-consulting.com< / a > , < a class = "reference" href = "mailto:jsiek@osl.iu.edu" > jsiek@ osl.iu.edu< / a > , < a class = "last reference" href = "mailto:witt@ive.uni-hannover.de" > witt@ ive.uni-hannover.de< / a > < / td > < / tr >
< tr > < th class = "docinfo-name" > Organization:< / th >
< td > < a class = "first reference" href = "http://www.boost-consulting.com" > Boost Consulting< / a > , Indiana University < a class = "reference" href = "http://www.osl.iu.edu" > Open Systems
Lab< / a > , University of Hanover < a class = "last reference" href = "http://www.ive.uni-hannover.de" > Institute for Transport
Railway Operation and Construction< / a > < / td > < / tr >
< tr > < th class = "docinfo-name" > Date:< / th >
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< td > 2004-01-12< / td > < / tr >
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< tr > < th class = "docinfo-name" > Copyright:< / th >
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< td > Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved< / td > < / tr >
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< / tbody >
< / table >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > abstract:< / th > < td class = "field-body" > < / td >
< / tr >
< / tbody >
< / table >
< p > The indirect iterator adapts an iterator by applying an < em > extra< / em >
dereference inside of < tt class = "literal" > < span class = "pre" > operator*()< / span > < / tt > . For example, this iterator
adaptor makes it possible to view a container of pointers
(e.g. < tt class = "literal" > < span class = "pre" > list< foo*> < / span > < / tt > ) as if it were a container of the pointed-to type
(e.g. < tt class = "literal" > < span class = "pre" > list< foo> < / span > < / tt > ) .< / p >
<!-- At some point we should add the capability to handle
iterators over smart pointers, which the impl handles. -JGS -->
< div class = "contents topic" id = "table-of-contents" >
< p class = "topic-title" > < a name = "table-of-contents" > Table of Contents< / a > < / p >
< ul class = "simple" >
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< li > < a class = "reference" href = "#indirect-iterator-synopsis" id = "id2" name = "id2" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > synopsis< / a > < / li >
< li > < a class = "reference" href = "#indirect-iterator-requirements" id = "id3" name = "id3" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#indirect-iterator-models" id = "id4" name = "id4" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#indirect-iterator-operations" id = "id5" name = "id5" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > operations< / a > < / li >
< li > < a class = "reference" href = "#example" id = "id6" name = "id6" > Example< / a > < / li >
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< / ul >
< / div >
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< div class = "section" id = "indirect-iterator-synopsis" >
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< h1 > < a class = "toc-backref" href = "#id2" name = "indirect-iterator-synopsis" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > synopsis< / a > < / h1 >
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< pre class = "literal-block" >
template <
class Iterator
, class Value = use_default
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, class CategoryOrTraversal = use_default
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, class Reference = use_default
, class Difference = use_default
>
class indirect_iterator
{
public:
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typedef /* see below */ value_type;
typedef /* see below */ reference;
typedef /* see below */ pointer;
typedef /* see below */ difference_type;
typedef /* see below */ iterator_category;
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indirect_iterator();
indirect_iterator(Iterator x);
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template <
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class Iterator2, class Value2, class Category2
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, class Reference2, class Difference2
>
indirect_iterator(
indirect_iterator<
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Iterator2, Value2, Category2, Reference2, Difference2
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> const& y
, typename enable_if_convertible< Iterator2, Iterator> ::type* = 0 // exposition
);
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Iterator base() const;
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reference operator*() const;
indirect_iterator& operator++();
indirect_iterator& operator--();
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private:
Iterator m_iterator; // exposition
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};
< / pre >
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< p > The member types of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > are defined according to the
following pseudo-code. We use the abbreviation
< tt class = "literal" > < span class = "pre" > V=iterator_traits< Iterator> ::value_type< / span > < / tt > .:< / p >
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< pre class = "literal-block" >
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if (Value is use_default) then
typedef iterator_traits< V> ::value_type value_type;
else
typedef remove_const< Value> ::type value_type;
if (Reference is use_default) then
if (Value is use_default) then
typedef iterator_traits< V> ::reference reference;
else
typedef Value& reference;
else
typedef Reference reference;
if (Value is use_default) then
typedef ?? pointer;
else
typedef Value* pointer;
if (Difference is use_default)
typedef iterator_traits< Iterator> ::difference_type difference_type;
else
typedef Difference difference_type;
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< / pre >
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< p > The member < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is a type that satisfies the
requirements of the concepts modeled by the < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > as
specified in the models section.< / p >
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< / div >
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< div class = "section" id = "indirect-iterator-requirements" >
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< h1 > < a class = "toc-backref" href = "#id3" name = "indirect-iterator-requirements" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > requirements< / a > < / h1 >
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< p > The < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument shall meet the requirements of Readable
Iterator. The < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt > argument shall be one of the
standard iterator tags or < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > . If < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt >
is an iterator tag, the template parameter < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument shall
meet the traversal requirements corresponding to the iterator tag.< / p >
< p > The expression < tt class = "literal" > < span class = "pre" > *v< / span > < / tt > , where < tt class = "literal" > < span class = "pre" > v< / span > < / tt > is an object of type
< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > , must be a valid expression
and must be convertible to < tt class = "literal" > < span class = "pre" > indirect_iterator::reference< / span > < / tt > . Also
< tt class = "literal" > < span class = "pre" > indirect_iterator::reference< / span > < / tt > must be convertible to
< tt class = "literal" > < span class = "pre" > indirect_iterator::value< / span > < / tt > . There are further requirements on the
< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > if the < tt class = "literal" > < span class = "pre" > Value< / span > < / tt > parameter
is not < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > , as implied by the algorithm for deducing the
default for the < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > member.< / p >
< / div >
< div class = "section" id = "indirect-iterator-models" >
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< h1 > < a class = "toc-backref" href = "#id4" name = "indirect-iterator-models" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models< / a > < / h1 >
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< p > If < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt > is a standard iterator tag,
< tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > is a model of the iterator concept corresponding
to the tag, otherwise < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > satisfies the requirements
of the most refined standard traversal concept that is satisfied by
the < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument.< / p >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models Readable Iterator. If
< tt class = "literal" > < span class = "pre" > indirect_iterator::reference(*v)< / span > < span class = "pre" > =< / span > < span class = "pre" > t< / span > < / tt > is a valid expression (where
< tt class = "literal" > < span class = "pre" > t< / span > < / tt > is an object of type < tt class = "literal" > < span class = "pre" > indirect_iterator::value_type< / span > < / tt > ) then
< tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models Writable Iterator. If
< tt class = "literal" > < span class = "pre" > indirect_iterator::reference< / span > < / tt > is a reference then
< tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models Lvalue Iterator.< / p >
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< / div >
< div class = "section" id = "indirect-iterator-operations" >
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< h1 > < a class = "toc-backref" href = "#id5" name = "indirect-iterator-operations" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > operations< / a > < / h1 >
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< p > In addition to the operations required by the concepts modeled by
< tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > , < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > provides the following
operations.< / p >
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< p > < tt class = "literal" > < span class = "pre" > indirect_iterator();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > must be Default Constructible.< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > with
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a default-constructed < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator(Iterator< / span > < span class = "pre" > x);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > with
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< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > copy constructed from < tt class = "literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template <
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class Iterator2, class Value2, unsigned Access, class Traversal
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, class Reference2, class Difference2
>
indirect_iterator(
indirect_iterator<
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Iterator2, Value2, Access, Traversal, Reference2, Difference2
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> const& y
, typename enable_if_convertible< Iterator2, Iterator> ::type* = 0 // exposition
);
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Iterator2< / span > < / tt > is implicitly convertible to < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > .< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > whose
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< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > subobject is constructed from < tt class = "literal" > < span class = "pre" > y.base()< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > **m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > ++m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > --m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< / div >
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< div class = "section" id = "example" >
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< h1 > < a class = "toc-backref" href = "#id6" name = "example" > Example< / a > < / h1 >
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< p > This example prints an array of characters, using
< tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > to access the array of characters through an
array of pointers. Next < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > is used with the
< tt class = "literal" > < span class = "pre" > transform< / span > < / tt > algorithm to copy the characters (incremented by one) to
another array. A constant indirect iterator is used for the source and
a mutable indirect iterator is used for the destination. The last part
of the example prints the original array of characters, but this time
using the < tt class = "literal" > < span class = "pre" > make_indirect_iterator< / span > < / tt > helper function.< / p >
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< pre class = "literal-block" >
char characters[] = " abcdefg" ;
const int N = sizeof(characters)/sizeof(char) - 1; // -1 since characters has a null char
char* pointers_to_chars[N]; // at the end.
for (int i = 0; i < N; ++i)
pointers_to_chars[i] = & characters[i];
// Example of using indirect_iterator
boost::indirect_iterator< char**, char>
indirect_first(pointers_to_chars), indirect_last(pointers_to_chars + N);
std::copy(indirect_first, indirect_last, std::ostream_iterator< char> (std::cout, " ," ));
std::cout < < std::endl;
// Example of making mutable and constant indirect iterators
char mutable_characters[N];
char* pointers_to_mutable_chars[N];
for (int j = 0; j < N; ++j)
pointers_to_mutable_chars[j] = & mutable_characters[j];
boost::indirect_iterator< char* const*> mutable_indirect_first(pointers_to_mutable_chars),
mutable_indirect_last(pointers_to_mutable_chars + N);
boost::indirect_iterator< char* const*, char const> const_indirect_first(pointers_to_chars),
const_indirect_last(pointers_to_chars + N);
std::transform(const_indirect_first, const_indirect_last,
mutable_indirect_first, std::bind1st(std::plus< char> (), 1));
std::copy(mutable_indirect_first, mutable_indirect_last,
std::ostream_iterator< char> (std::cout, " ," ));
std::cout < < std::endl;
// Example of using make_indirect_iterator()
std::copy(boost::make_indirect_iterator(pointers_to_chars),
boost::make_indirect_iterator(pointers_to_chars + N),
std::ostream_iterator< char> (std::cout, " ," ));
std::cout < < std::endl;
< / pre >
< p > The output is:< / p >
< pre class = "literal-block" >
a,b,c,d,e,f,g,
b,c,d,e,f,g,h,
a,b,c,d,e,f,g,
< / pre >
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< p > The source code for this example can be found < a class = "reference" href = "../example/indirect_iterator_example.cpp" > here< / a > .< / p >
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< / div >
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< / div >
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< hr class = "footer" / >
< div class = "footer" >
< a class = "reference" href = "indirect_iterator.rst" > View document source< / a > .
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Generated on: 2004-01-12 19:01 UTC.
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Generated by < a class = "reference" href = "http://docutils.sourceforge.net/" > Docutils< / a > from < a class = "reference" href = "http://docutils.sourceforge.net/rst.html" > reStructuredText< / a > source.
< / div >
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< / body >
< / html >
