Re: ostream_iterator and the delimiter before the item

"Alf P. Steinbach" <>
Mon, 15 Jun 2009 23:09:28 +0200
* ShaunJ:

I often need to output a list with a delimiter (such as a tab or a
comma) before the item rather than after (which is where the end-of-
line will go). ostream_iterator puts the delimiter after the item. Is
there a simple solution for creating an ostream_iterator that puts the
delimiter before the item?

If I do it in a for loop, it's easy, of course. But the function I'm
calling takes an output iterator parameter, and to use a for loop I
would have to store all the results in a list first, which would take
a bunch of memory and is totally unnecessary.

     class TabbedIntIter
         std::ostream* pMyStream;
         typedef char char_type;
         typedef std::ostream ostream_type;
         typedef std::ostream::traits_type traits_type;

         TabbedIntIter( std::ostream& stream )
             : pMyStream( &stream )

         TabbedIntIter& operator*() { return *this; }
         TabbedIntIter& operator++() { return *this; }

         TabbedIntIter& operator=( int x )
             (*pMyStream) << '\t' << x;
             return *this;

     int main()
         foo( TabbedIntIter( std::cout ) );

Cheers & hth.,

- Alf

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