1 // Copyright Vladimir Prus 2004. 2 // Distributed under the Boost Software License, Version 1.0. 3 // (See accompanying file LICENSE_1_0.txt 4 // or copy at http://www.boost.org/LICENSE_1_0.txt) 5 6 #ifndef BOOST_EOF_ITERATOR_VP_2004_03_12 7 #define BOOST_EOF_ITERATOR_VP_2004_03_12 8 9 #include <boost/iterator/iterator_facade.hpp> 10 11 namespace boost { 12 13 /** The 'eof_iterator' class is useful for constructing forward iterators 14 in cases where iterator extract data from some source and it's easy 15 to detect 'eof' \-- i.e. the situation where there's no data. One 16 apparent example is reading lines from a file. 17 18 Implementing such iterators using 'iterator_facade' directly would 19 require to create class with three core operation, a couple of 20 constructors. When using 'eof_iterator', the derived class should define 21 only one method to get new value, plus a couple of constructors. 22 23 The basic idea is that iterator has 'eof' bit. Two iterators are equal 24 only if both have their 'eof' bits set. The 'get' method either obtains 25 the new value or sets the 'eof' bit. 26 27 Specifically, derived class should define: 28 29 1. A default constructor, which creates iterator with 'eof' bit set. The 30 constructor body should call 'found_eof' method defined here. 31 2. Some other constructor. It should initialize some 'data pointer' used 32 in iterator operation and then call 'get'. 33 3. The 'get' method. It should operate this way: 34 - look at some 'data pointer' to see if new element is available; 35 if not, it should call 'found_eof'. 36 - extract new element and store it at location returned by the 'value' 37 method. 38 - advance the data pointer. 39 40 Essentially, the 'get' method has the functionality of both 'increment' 41 and 'dereference'. It's very good for the cases where data extraction 42 implicitly moves data pointer, like for stream operation. 43 */ 44 template<class Derived, class ValueType> 45 class eof_iterator : public iterator_facade<Derived, const ValueType, 46 forward_traversal_tag> 47 { 48 public: eof_iterator()49 eof_iterator() 50 : m_at_eof(false) 51 {} 52 53 protected: // interface for derived 54 55 /** Returns the reference which should be used by derived 56 class to store the next value. */ value()57 ValueType& value() 58 { 59 return m_value; 60 } 61 62 /** Should be called by derived class to indicate that it can't 63 produce next element. */ found_eof()64 void found_eof() 65 { 66 m_at_eof = true; 67 } 68 69 70 private: // iterator core operations 71 #ifdef __DCC__ 72 friend class boost::iterator_core_access; 73 #else 74 friend class iterator_core_access; 75 #endif 76 increment()77 void increment() 78 { 79 static_cast<Derived&>(*this).get(); 80 } 81 equal(const eof_iterator & other) const82 bool equal(const eof_iterator& other) const 83 { 84 if (m_at_eof && other.m_at_eof) 85 return true; 86 else 87 return false; 88 } 89 dereference() const90 const ValueType& dereference() const 91 { 92 return m_value; 93 } 94 95 bool m_at_eof; 96 ValueType m_value; 97 }; 98 } 99 100 #endif 101 102