The following is an example of how to use the -transform_iterator_generator class to iterate through a range of -numbers, multiplying each of them by 2 when they are dereferenced. +transform_iterator_generator class to iterate through a range +of numbers, multiplying each of them by 2 when they are dereferenced. +The boost::binder1st class is used instead of the standard +one because tranform iterator requires the function object to be +Default Constructible.
@@ -80,16 +83,18 @@ numbers, multiplying each of them by 2 when they are dereferenced.
#include <iostream>
#include <boost/iterator_adaptors.hpp>
+// definition of class boost::binder1st and function boost::bind1st() ...
+
int
main(int, char*[])
{
int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
- typedef std::binder1st< std::multiplies<int> > Function;
+ typedef boost::binder1st< std::multiplies<int> > Function;
typedef boost::transform_iterator_generator<Function, int*>::type doubling_iterator;
- doubling_iterator i(x, std::bind1st(std::multiplies<int>(), 2)),
- i_end(x + sizeof(x)/sizeof(int), std::bind1st(std::multiplies<int>(), 2));
+ doubling_iterator i(x, boost::bind1st(std::multiplies<int>(), 2)),
+ i_end(x + sizeof(x)/sizeof(int), boost::bind1st(std::multiplies<int>(), 2));
std::cout << "multiplying the array by 2:" << std::endl;
while (i != i_end)
@@ -111,14 +116,17 @@ The output from this part is:
-AdaptableUnaryFunction
+AdaptableUnaryFunction
The function object that transforms each element in the iterator
range. The argument_type of the function object must match
the value type of the base iterator. The result_type of the
function object will be the resulting iterator's
value_type. If you want the resulting iterator to behave as
an iterator, the result of the function should be solely a function of
-its argument.
+its argument. Also, the function object must be Default
+Constructible (which many of the standard function objects are not).
@@ -173,8 +181,8 @@ function to add four to each element of the array.
std::cout << "adding 4 to each element in the array:" << std::endl;
- std::copy(boost::make_transform_iterator(x, std::bind1st(std::plus(), 4)),
- boost::make_transform_iterator(x + N, std::bind1st(std::plus(), 4)),
+ std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus(), 4)),
+ boost::make_transform_iterator(x + N, boost::bind1st(std::plus(), 4)),
std::ostream_iterator(std::cout, " "));
std::cout << std::endl;