[boost] RE: ublas iterator problem

From: Neal Becker (ndbecker2_at_[hidden])
Date: 2004-09-08 19:09:58

Stefan Seefeld wrote:

> 
>> From: Neal D. Becker [mailto:ndbecker2_at_[hidden]]
>> Sent: September 8, 2004 15:59
> 
>> u.begin() should return an iterator, and the iterator should define
>> operator[].  Why doesn't this work?
> 
> huh ? Which iterator defines operator[] ? It may define
> operator+(size_type) or similar, if it allows random access, but not
> operator[]. If you know your container manages contiguous memory you may
> use '&*u.begin()' to access the raw memory, and apply your operator[] to
> that.
> 
Consider this:

#include <vector>
#include <boost/numeric/ublas/vector.hpp>

template<typename it_t>
int adder (it_t in, int cnt) {
  int sum = 0;
  for (int i = 0; i < cnt; i++)
    sum += in[i];
  return sum;
}

int main() {
  std::vector<int> a (10);
  adder (a.begin(), 10);  << this is OK

  boost::numeric::ublas::vector<int> b;
  adder (b.begin(), 10);  << error, why?
}

g++34 -I /usr/local/src/boost.cvs -c Test.cc
Test.cc: In function `int adder(it_t, int) [with it_t =
boost::numeric::ublas::vector<int,
boost::numeric::ublas::unbounded_array<int, std::allocator<int> >
>::iterator]':
Test.cc:17:   instantiated from here
Test.cc:8: error: no match for 'operator[]' in 'in[i]'