I'm not sure if this is the fault of transform_iterator----I really don't see how it could be----but I'm really confused here.
I've got an unordered_map (typedefed to GroupMap) in my class. The specifics of those types don't matter except that GroupID is an integral type, and Group contains a std::vector vec.
I'm trying to use a transform_iterator so that my class may be viewed as a group container:
typedef boost::transform_iterator const_iterator;
const_iterator begin() const
{
return boost::make_transform_iterator(currgroups.begin(),GroupSelector());
}
const_iterator end() const
{
return boost::make_transform_iterator(currgroups.end(),GroupSelector());
}
std::pair groups() const
{
const Group &grp = *(begin());
return std::make_pair(begin(),end());
}
Where my GroupSelector class is defined as
struct GroupSelector
{
typedef const Group& result_type;
const Group& operator()(const std::pair &p) const
{
std::cout << p.second.vec.size() << " " << &p.second << std::endl;
return p.second;
}
};
Note the output statement. Now, the usage in my main function is
for (tie(iter,end) = final.groups(); iter != end; ++iter)
{
const Group& grp = *iter;
cerr << &grp << endl;
cerr << grp.segs.size() << endl;
...
My output is
10 0012F50C
10 0012F65C
0012F65C
1243176
which is strange for two reasons. The first line comes from GroupSelector when I dereference begin() in the groups() function. The second comes from GroupSelector when I dereference iter in main. As these should both correspond to the same iterator, I can't understand why the address of the returned Group reference is different.
The 3rd and 4th lines are outputted in main. Here's the second confusion: The address for the Group object is the same as in the most recent GroupSelector output, yet now the size of the vector within the Group comes out wrong. HUH?
