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added stuff about Default Constructible needed for the function object

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[SVN r9683]
This commit is contained in:
Jeremy Siek 2001-03-29 16:26:42 +00:00
parent d6d88db6e8
commit cf1296dff8
1 changed files with 17 additions and 9 deletions
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26
transform_iterator.htm
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@ -71,8 +71,11 @@ public:
<p> <p>
The following is an example of how to use the The following is an example of how to use the
<tt>transform_iterator_generator</tt> class to iterate through a range of <tt>transform_iterator_generator</tt> class to iterate through a range
numbers, multiplying each of them by 2 when they are dereferenced. of numbers, multiplying each of them by 2 when they are dereferenced.
The <tt>boost::binder1st</tt> class is used instead of the standard
one because tranform iterator requires the function object to be
Default Constructible.
<p> <p>
<PRE> <PRE>
@ -80,16 +83,18 @@ numbers, multiplying each of them by 2 when they are dereferenced.
#include &lt;iostream&gt; #include &lt;iostream&gt;
#include &lt;boost/iterator_adaptors.hpp&gt; #include &lt;boost/iterator_adaptors.hpp&gt;
// definition of class boost::binder1st and function boost::bind1st() ...
int int
main(int, char*[]) main(int, char*[])
{ {
int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 }; int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
typedef std::binder1st&lt; std::multiplies&lt;int&gt; &gt; Function; typedef boost::binder1st&lt; std::multiplies&lt;int&gt; &gt; Function;
typedef boost::transform_iterator_generator&lt;Function, int*&gt;::type doubling_iterator; typedef boost::transform_iterator_generator&lt;Function, int*&gt;::type doubling_iterator;
doubling_iterator i(x, std::bind1st(std::multiplies&lt;int&gt;(), 2)), doubling_iterator i(x, boost::bind1st(std::multiplies&lt;int&gt;(), 2)),
i_end(x + sizeof(x)/sizeof(int), std::bind1st(std::multiplies&lt;int&gt;(), 2)); i_end(x + sizeof(x)/sizeof(int), boost::bind1st(std::multiplies&lt;int&gt;(), 2));
std::cout &lt;&lt; "multiplying the array by 2:" &lt;&lt; std::endl; std::cout &lt;&lt; "multiplying the array by 2:" &lt;&lt; std::endl;
while (i != i_end) while (i != i_end)
@ -111,14 +116,17 @@ The output from this part is:
</TR> </TR>
<TR> <TR>
<TD><a href="http://www.sgi.com/tech/stl/AdaptableUnaryFunction.html"><tt>AdaptableUnaryFunction</tt></a></TD> <TD><a
href="http://www.sgi.com/tech/stl/AdaptableUnaryFunction.html"><tt>AdaptableUnaryFunction</tt></a></TD>
<TD>The function object that transforms each element in the iterator <TD>The function object that transforms each element in the iterator
range. The <tt>argument_type</tt> of the function object must match range. The <tt>argument_type</tt> of the function object must match
the value type of the base iterator. The <tt>result_type</tt> of the the value type of the base iterator. The <tt>result_type</tt> of the
function object will be the resulting iterator's function object will be the resulting iterator's
<tt>value_type</tt>. If you want the resulting iterator to behave as <tt>value_type</tt>. If you want the resulting iterator to behave as
an iterator, the result of the function should be solely a function of an iterator, the result of the function should be solely a function of
its argument.</TD> its argument. Also, the function object must be <a
href="http://www.sgi.com/tech/stl/DefaultConstructible.html"> Default
Constructible</a> (which many of the standard function objects are not).</TD>
</TR> </TR>
<TR> <TR>
@ -173,8 +181,8 @@ function to add four to each element of the array.
<pre> <pre>
std::cout << "adding 4 to each element in the array:" << std::endl; std::cout << "adding 4 to each element in the array:" << std::endl;
std::copy(boost::make_transform_iterator(x, std::bind1st(std::plus<int>(), 4)), std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus<int>(), 4)),
boost::make_transform_iterator(x + N, std::bind1st(std::plus<int>(), 4)), boost::make_transform_iterator(x + N, boost::bind1st(std::plus<int>(), 4)),
std::ostream_iterator<int>(std::cout, " ")); std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl; std::cout << std::endl;