diff --git a/counting_iterator.htm b/counting_iterator.htm new file mode 100644 index 0000000..cd8685e --- /dev/null +++ b/counting_iterator.htm @@ -0,0 +1,186 @@ + + + + + + +Counting Iterator Adaptor Documentation + + + + +c++boost.gif (8819 bytes) + +

Counting Iterator Adaptor

+ +Defined in header +boost/counting_iterator.hpp + +

+Sometimes it would be nice if one could treat an integer like an +iterator, for example, to fill up a vector with the numbers zero +through one hundred using std::copy(). The +only iterator operation missing from builtin integer types is an +operator*(), which we would want to just return the current +value of the integer. The counting iterator adaptor provides this +functionality, though it is a bit more generalized. One can use the +counting iterator adaptor not only with integer types, but with any +type that is incrementable (has operator++()). The following +pseudo-code shows the general idea of how the counting iterator is +implemented. +

+ +
+  // inside a hypothetical counting_iterator class...
+  typedef Incrementable value_type;
+  value_type counting_iterator::operator*() const {
+    return this->base; // no dereference!
+  }
+
+ +All of the other operators of the counting iterator behave in the same +fashion as the incrementable base type. + +

Synopsis

+ +
+namespace boost {
+  template <class Incrementable>
+  struct counting_iterator_generator;
+
+  template <class Incrementable>
+  typename counting_iterator_generator<Incrementable>::type
+  make_counting_iterator(Incrementable x);
+}
+
+ +
+ +

The Counting Iterator Type +Generator

+ +The class counting_iterator_generator is a helper class whose +purpose is to construct a counting iterator type. The template +parameters for this class is the Incrementable type that is +being wrapped. + +
+template <class Incrementable>
+class counting_iterator_generator
+{
+public:
+    typedef iterator_adaptor<...> type;
+};
+
+ +

Example

+ +In this example we use the counting iterator generator to create a +counting iterator, and count from zero to four. + +
+#include <boost/config.hpp>
+#include <iostream>
+#include <boost/counting_iterator.hpp>
+
+int main(int, char*[])
+{
+  // Example of using counting_iterator_generator
+  std::cout << "counting from 0 to 4:" << std::endl;
+  boost::counting_iterator_generator<int>::type first(0), last(4);
+  std::copy(first, last, std::ostream_iterator<int>(std::cout, " "));
+  std::cout << std::endl;
+
+  // to be continued...
+
+ + +

Template Parameters

+ + + + + + + + + + + +
ParameterDescription
IncrementableThe type being wrapped by the adaptor.
+ +

Model of

+ +If the Incrementable type has all of the functionality of a +Random +Access Iterator except the operator*(), then the counting +iterator will be a model of Random +Access Iterator. In the Incrementable type has less +functionality, then the counting iterator will have correspondingly +less functionality. + +

Members

+ +The counting iterator type implements the member functions and +operators required of the Random +Access Iterator concept. In addition it has the following +constructor: + +
+counting_iterator_generator::type(const Incrementable& i)
+
+ +

+

+

+ + +

The Counting Iterator Object Generator

+ +
+template <class Incrementable>
+typename counting_iterator_generator<Incrementable>::type
+make_counting_iterator(Incrementable base);
+
+ +This function provides a convenient way to create counting iterators. + +

Example

+ +In this example we count from negative five to positive five, this +time using the make_counting_iterator() function to save some +typing. + +
+  // continuing from previous example...
+  std::cout << "counting from -5 to 5:" << std::endl;
+  std::copy(boost::make_counting_iterator(-5),
+	    boost::make_counting_iterator(5),
+	    std::ostream_iterator<int>(std::cout, " "));
+  std::cout << std::endl;
+
+
+  return 0;
+}
+
+ + +
+

Revised 10 Feb 2001

+

© Copyright Jeremy Siek 2000. Permission to copy, use, +modify, sell and distribute this document is granted provided this copyright +notice appears in all copies. This document is provided "as is" +without express or implied warranty, and with no claim as to its suitability for +any purpose.

+ + + + + + diff --git a/counting_iterator_example.cpp b/counting_iterator_example.cpp new file mode 100644 index 0000000..21d5fb0 --- /dev/null +++ b/counting_iterator_example.cpp @@ -0,0 +1,28 @@ +// (C) Copyright Jeremy Siek 2000. Permission to copy, use, modify, sell and +// distribute this software is granted provided this copyright notice appears +// in all copies. This software is provided "as is" without express or implied +// warranty, and with no claim as to its suitability for any purpose. + + +#include +#include +#include + +int main(int, char*[]) +{ + // Example of using counting_iterator_generator + std::cout << "counting from 0 to 4:" << std::endl; + boost::counting_iterator_generator::type first(0), last(4); + std::copy(first, last, std::ostream_iterator(std::cout, " ")); + std::cout << std::endl; + + // Example of using make_counting_iterator() + std::cout << "counting from -5 to 5:" << std::endl; + std::copy(boost::make_counting_iterator(-5), + boost::make_counting_iterator(5), + std::ostream_iterator(std::cout, " ")); + std::cout << std::endl; + + + return 0; +}