Robert Ramey <ramey@rrsd.com> writes:
I have a problem with the latest version of the new iterators. This is illustrated in the following example.
#include <strstream> #include <iterator> #include <boost/iterator/counting_iterator.hpp>
main(){ std::istrstream is("abcdefg"); typedef boost::counting_iterator<std::istream_iterator<char> > ci; const ci end = std::istream_iterator<char>(); // note the const !!!
I don't see why the const should be relevant.
ci begin = std::istream_iterator<char>(is);
Hmm, the implicit conversions from istream_iterator to the counting_iterator above are troubling. I think those constructors should be explicit.
unsigned int size;
// the following should fail at compilation ?
Why? OK, maybe it would be better to make it fail because the iterator is not in fact a random-access iterator.
// in fact it compiles are returns a value of -7 !!! size = begin - end;
// the following should compile and return a value of 7 // in fact, it compiles but goes into an infinite loop size = end - begin; }
I don't see why you think the first should compile but the second should not. If they're not random-access iterators, it seems to me that there's no reason you should be able to subtract them in any order. If they were random-access iterators, it would be unreasonable to expect the compiler to detect which one had an earlier position and disallow one subtraction.
Note that this problem did not appear with the first release candidate.
Also, if one follows the links from the main documentation page, one is directed to the documentation of the old iterators. This is extremely confusing. This has been pointed out before.
That's a serious problem which I'll fix immediately. -- Dave Abrahams Boost Consulting www.boost-consulting.com