How to read arbitrary number of values using std::copy?

Question

I\'m trying to code opposite action to this:

std::ostream outs; // properly initialized of course
std::set my_set; // ditto

outs << my_set.         


        

Answer 1

(Edited: I should have read the question closer...)

While somewhat suspect, you can get approximately the right behavior by having an entry in the file that will "fail" the first loop, then clear the fail bit on the stream and start reading more.

Data, without an explicit size, but like this

1 1 2 3 5 8 Fibb

Fed to the code below seems to do what I meant, at least on VS2005 with STLPort.

typedef std::istream_iterator < int, char, std::char_traits ,ptrdiff_t> is_iter;
std::copy( is_iter(cin), is_iter(), inserter(my_set,my_set.end()));
cin.clear();
std::cin >> instr;

Answer 2

How about using an alternate iterator to do the traversal and then use a function object (or lambda) to fill in the container?

istream ins;
set<int>::size_type size;
set<int> new_set;
ins >> size;
ostream_iterator<int> ins_iter(ins);

for_each(counting_iterator<int>(0), counting_iterator<int>(size),
  [&new_set, &ins_iter](int n) { new_set.insert(*ins_iter++); }
);

Of course this assumes you have a C++0x compliant compiler.

BTW, 'counting_iterator<>' is part of Boost.Iterator.