Re: [Boost-users] Clever simultaneous iteration over multiple containers

AMDG Joseph Wakeling wrote:

Dear Boost users,

A (possibly naïve) question, as I'm a reasonably competent C programmer but only a relative novice with C++, and just starting to get used to concepts from libraries like Boost.

The BOOST_FOREACH macro provides a nice way to iterate over all the contents of a container like a vector, list, etc. But what about when several containers are involved?

I'll give a concrete-ish example from a problem I'm working on. I have two vectors, vector v1 and vector<double> v2 where myClass is a base class and v1.size()==v2.size(). Then, what I want to do is,

for(unsigned int i=0;ifunc(v2.at(i));

That works, of course; I'm just wondering if there is a more elegant or compiler-friendly way of writing this along the lines of the BOOST_FOREACH macro. Initialising separate iterators for both v1 and v2 seems ugly/lots of boilerplate. I have seen the solution here: http://permalink.gmane.org/gmane.comp.lib.boost.user/31954

... but that seems less desirable because it involves using an extra library which I don't think is standard in Linux distros.

I have the impression that the zip_iterator boost lib is useful here, but did not fully understand if or how.

To use zip_iterator, you would need something like std::make_pair(boost::make_zip_iterator(boost::make_tuple(v1.begin(), v2.begin())), boost::make_zip_iterator(boost::make_tuple(v1.end(), v2.end()))); The RangeEx library which has been accepted, but is not yet in the trunk, also provides a zip operation that works with ranges instead of iterators. In Christ, Steven Watanabe