std::set as search tree - manipulate elements?

Hi all.

I would like to use std::set to implement a histogram.
In essence the histogram contains some elements

struct histbin{
           int bin;
           int count;
   /* constructors */
          bool operator<(const histbin& h) const {return bin < h.bin;};
};

where histbin::bin denotes the range of each bin and
histbin::count denotes the number of hits.

The problem is how to build the histogram. Since
std::set is specified to have O(log n) search time,
it must necessarily be implemented as some sort of
tree structure. I would like to exploit this to do
something like

std::set<histbin> histogram;

std::set<histbin>::iterator i;
while (/* data coming in */)
{
     i=histogram.find(data);
     if (i!=histogram.end())
     {
         (*i).count+=1; // <<<<<======
     }
     else
    {
       /* insert new bin */
    }
}

The problem is the tagged line. Apparently, all elements
in std::set are declared 'const', so I am not allowed to
manipulate the elements directly. Do note that I do *not*
manipulate the histbin::bin element, which is used as the
key for sorting, and thus it ought to be safe to manipulate
the histbin::count elements.

Is there a convemient, safe way to be able to use std::set
as the search tree for this histogram?

If 'no', are there other STL containesr that can be used?
I would prefer not to have to implement a tree from scratch,
but if there are no alternatives I would like to know that
early on, and just get to work...

Rune

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