ceph/src/boost/libs/iterator/example/transform_iterator_example.cpp

   1 // (C) Copyright Jeremy Siek 2000-2004.
   2 // Distributed under the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5
   6
   7 #include <functional>
   8 #include <algorithm>
   9 #include <iostream>
  10 #include <boost/iterator/transform_iterator.hpp>
  11
  12 // What a bummer. We can't use std::binder1st with transform iterator
  13 // because it does not have a default constructor. Here's a version
  14 // that does.
  15
  16 namespace boost {
  17
  18   template <class Operation>
  19   class binder1st
  20     : public std::unary_function<typename Operation::second_argument_type,
  21                                  typename Operation::result_type> {
  22   protected:
  23     Operation op;
  24     typename Operation::first_argument_type value;
  25   public:
  26     binder1st() { } // this had to be added!
  27     binder1st(const Operation& x,
  28               const typename Operation::first_argument_type& y)
  29         : op(x), value(y) {}
  30     typename Operation::result_type
  31     operator()(const typename Operation::second_argument_type& x) const {
  32       return op(value, x);
  33     }
  34   };
  35
  36   template <class Operation, class T>
  37   inline binder1st<Operation> bind1st(const Operation& op, const T& x) {
  38     typedef typename Operation::first_argument_type arg1_type;
  39     return binder1st<Operation>(op, arg1_type(x));
  40   }
  41
  42 } // namespace boost
  43
  44 int
  45 main(int, char*[])
  46 {
  47   // This is a simple example of using the transform_iterators class to
  48   // generate iterators that multiply the value returned by dereferencing
  49   // the iterator. In this case we are multiplying by 2.
  50   // Would be cooler to use lambda library in this example.
  51
  52   int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
  53   const int N = sizeof(x)/sizeof(int);
  54
  55   typedef boost::binder1st< std::multiplies<int> > Function;
  56   typedef boost::transform_iterator<Function, int*> doubling_iterator;
  57
  58   doubling_iterator i(x, boost::bind1st(std::multiplies<int>(), 2)),
  59     i_end(x + N, boost::bind1st(std::multiplies<int>(), 2));
  60
  61   std::cout << "multiplying the array by 2:" << std::endl;
  62   while (i != i_end)
  63     std::cout << *i++ << " ";
  64   std::cout << std::endl;
  65
  66   std::cout << "adding 4 to each element in the array:" << std::endl;
  67
  68   std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus<int>(), 4)),
  69             boost::make_transform_iterator(x + N, boost::bind1st(std::plus<int>(), 4)),
  70             std::ostream_iterator<int>(std::cout, " "));
  71   std::cout << std::endl;
  72
  73   return 0;
  74 }
  75
  76