Re: How to create custom iterator for use with std::copy?

In article <4456612e$1@mamba.>,
 "Siegfried Heintze" <siegfried@heintze.com> wrote:


Try it.

class MyIter
{
}

int main()
{
   copy( MyIter...

OK, apparently we need at least one constructor...

class MyIter
{
public:
   MyIter();
};

int main()
{
   copy( MyIter(), ...

Well, now we need some way of creating two different objects of the same
type...

class MyIter
{
public:
   MyIter();
   MyIter( int v );
};

int main()
{
   copy( MyIter(), MyIter( 7 ), ostream_iterator<...

OK, what does a MyIter contain? Let's just have it hold ints...

int main()
{
   copy( MyIter(), MyIter( 7 ), ostream_iterator<int>( cout ) );
}

Now try to compile it and it will tell you what functions are missing.
It's fun!

Here is one I came up with...

class fibonacci:
                  public std::iterator< std::forward_iterator_tag, int >
{
   int prev_value, value, max;
public:
   fibonacci(): prev_value(0), value(0), max(0) { }

   explicit fibonacci(int m): prev_value(0), value(1), max(m) { }

   const int operator*() const { return value; }

   fibonacci& operator++()
   {
      int tmp = value;
      value += prev_value;
      prev_value = tmp;
      return *this;
   }
   
   fibonacci operator++(int)
   {
      fibonacci tmp(*this);
      ++(*this);
      return tmp;
   }

   friend bool operator==(const fibonacci& lhs, const fibonacci& rhs)
   {
      bool result = false;
      if ( lhs.value == 0 && rhs.value == 0 )
         result = true;
      else if ( rhs.value == 0 && !( lhs.value < lhs.max ) )
         result = true;
      else if ( lhs.value == 0 && !( rhs.value < rhs.max ) )
         result = true;
      else if ( lhs.prev_value == rhs.prev_value
                        && lhs.value == rhs.value && lhs.max == rhs.max )
         result = true;
      return result;
   }
};

bool operator!=(const fibonacci& lhs, const fibonacci& rhs) {
   return !(lhs == rhs);
}