Re: [Boost-users] Using Boost string library

From: Meryl Silverburgh (silverburgh.meryl_at_[hidden])
Date: 2007-02-19 16:33:52

On 2/19/07, Pavol Droba <droba_at_[hidden]> wrote:
> Meryl Silverburgh wrote:
> > On 2/18/07, Pavol Droba <droba_at_[hidden]> wrote:
> >> Hi,
> >>
> >> Meryl Silverburgh wrote:
> >>> Thanks for your idea.
> >>>
> >>> I have cases like this:
> >>>
> >>> /1/1
> >>> /1/2/3/2
> >>>
> >>> Since the first string /1/1 is smaller than the /1/2 (1 is < 2) of the
> >>> /1/2/3/2, I should able to stop comparison by looking at the 4th
> >>> character (/1/2) of '/1/2/3/2'.
> >>>
> >>> So for cases like that, I would like to stop as soon as i can tell one
> >>> string is shorter than the other, instead of splitting the whole
> >>> string.
> >>>
> >>>
> >>>
> >> This is exactly what would happen you use the second approach I gave you.
> >> Constructing the iterator_range from the split iterator does not perform
> >> any actual searching, and lexicographical_compare stops on the first
> >> possible index (i.e on the first position where inputs are different).
> >>
> >>
> >>>> You can even throw away the vector, and directly create an
> >>>> iterator_range from the split_iterator. This way you may spare some
> >>>> unnecessary tokenization.
> >>>>
> >>>> typedef split_iterator<string::const_iterator> string_split;
> >>>> iterator_range<string_split> r1(
> >>>>         make_split_iterator(s1, is_any_of("/")), string_split())
> >>>>
> >>>> iterator_range<string_split> r2(
> >>>>         make_split_iterator(s2, is_any_of("/")), string_split())
> >>>>
> >>>> if(lexicographical_compare(r1, r2, integer_compare))
> >>>> {
> >>>>         // s1 is less
> >>>> }
> >> Regards,
> >> Pavol
> >
> > Pavol,
> >
> > Thanks for your help. I am trying your second approach.  But I am
> > having compilation error in this line:
> > iterator_range<string_split> r1(
> >                       make_split_iterator(s1, is_any_of("/")), string_split());
> > error:
> > ../test.cpp:18: error: no matching function for call to
> > `boost::algorithm::iterator_range<string_split>::iterator_range(boost::algorithm::split_iterator<__gnu_cxx::__normal_iterator<char*,
> > std::basic_string<char, std::char_traits<char>, std::allocator<char> >
> >>> , string_split)'
> > /usr/include/boost/algorithm/string/iterator_range.hpp:89: note:
> > candidates are:
> > boost::algorithm::iterator_range<IteratorT>::iterator_range(const
> > boost::algorithm::iterator_range<IteratorT>&) [with IteratorT =
> > string_split]
> > /usr/include/boost/algorithm/string/iterator_range.hpp:85: note:
> >
> > Complete program:
> > #include <iostream>
> > #include <string>
> >
> > #include "boost/algorithm/string/find_iterator.hpp"
> > #include "boost/algorithm/string/classification.hpp"
> > using namespace std;
> > using namespace boost::algorithm;
> >
> > typedef split_iterator<string::const_iterator> string_split;
> >
> > int main(int argc, char **argv) {
> >       cout << "hello world" << endl;
> >
> >       string s1("/1/1/2");
> >       string s2("/1/1/3");
> >
> >       iterator_range<string_split> r1(
> >                       make_split_iterator(s1, is_any_of("/")), string_split());
> >
> >               iterator_range<string_split> r2(
> >                       make_split_iterator(s2, is_any_of("/")), string_split());
> >
> >               if(lexicographical_compare(r1, r2, integer_compare))
> >               {
> >                       cout << " s1 is less " << endl;
> >               } else {
> >                       cout << " s2 is less " << endl;
> >               }
> >               }
> >
> > }
> >
>
> The problem is with template instantiation. Since you are passing
> "string" and not "const string" as an argument to make_split_iterator,
> the resulting type is actualy split_iterator<string::iterator>. This is
> not the same (nor convertible) to split_iterator<string::const_iterator>.
>
> So the simple fix would be to change the definition of the string_split
> to split_iterator<string::iterator>.
>
In addition, you will need to implement integer_compare.
> In addition, you will need to implement integer_compare. I have not
> included it in may mail.

Thanks. I notice that.  Can you please help me understand how to
implement integer_compare (a predicate comparision object)?

What are the input type?
bool operator() (const ? &a, const ? &b) ?

and if the input strings are  '/1/1/5' and '1/1/10'
what will be passed to the integer_compare?

> Please, don't take my code as 100% correct. I didn't actualy compile it,
> I just wanted to gived you an idea which way to go. Anyway, I'll be glad
> to help you if you have any further questions.
>
> Regards,
> Pavol.
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