Re: [Boost-users] [string_algo] Split and Predicates

From: Pavol Droba (droba_at_[hidden])
Date: 2005-01-28 02:11:03

Hi,

On Thu, Jan 27, 2005 at 03:38:04PM -0800, David Brownell wrote:
> I am attempting to split a string with the string_algo library, using the
> code below.  It appears that the split algorithm is designed to split on
> instances of individual characters rather than sequences of characters.  Is
> there something I can do to split on a substring?  The code below
> illustrates the problem, where I am forces to use the is_any_of predicate
> rather than something that implies equality.  It seems like this is a
> trivial use of the algorithm, so there could easily be something that I am
> missing.  
> 
>     typedef std::vector<boost::iterator_range<char const *> >
> ResultsType;
> 
>     ResultsType             results;
>     static char const       STRING[] = "this\r\nis\r\n\r\na test!";
> 
>     boost::split(results, 
>                  boost::iterator_range<char const *>(STRING, STRING +
> sizeof(STRING)), 
>                  boost::is_any_of("\r\n"));  // The problem is here.  I
> would like to be able 
>                                              // to use something like
> equals, but split requires 
>                                              // a predicate that takes a
> single argument rather than 
>                                              // a range.
> 
>     for(ResultsType::const_iterator rptr = results.begin(); 
>         rptr != results.end(); 
>         ++rptr)
>             std::cout << "'" << std::string(rptr->begin(), rptr->end()) <<
> "'\n";
> 

It is possible to achieve what you want quite easily. However, split algorithm
is not the right tool for this.
Split is a high level wrapper over the split_iterator and it is quite specialized.

So this is the code, that should work for you:

   #include <boost/algorithm/string/find_iterator.hpp>
   #include <boost/algorithm/string/finder.hpp>

   static char const       STRING[] = "this\r\nis\r\n\r\na test!";

   typedef boost::split_iterator<const char*> char_split_iterator;

   for(char_split_iterator It=char_split_iterator(STRING, boost::first_finder("\r\n");
       It!=char_split_iterator();
       ++It)
    {
        cout << *It << endl;
    }

This example will split the STRING in the tokens, delimited by "\r\n".
Note, that instead of first_finder, you can use any other one. Even the custom one.
Check the documentation for more details.
There is also an example in boost/libs/algorithm/string/example/split_example.cpp

Regards,

Pavol

PS: I have not tried to compile the example, so please be patient it there are some errors.