[gecode-users] Formatting of Int view output

[Chris Mears]

Hello,

In Gecode 2.2.0 the formatting of integer variables doesn't quite work
correctly.  For example, I tried to print a matrix of variables with
padding, like this:

    for (int i = 0 ; i < 6 ; i++)
    {
        for (int j = 0 ; j < 6 ; j++)
            cout << setw(15) << m(i,j);
        cout << endl;
    }

"m" is a Matrix<IntVarArray>.  "setw(15)" is intended to make each
element of the matrix use 15 characters, right-justified.  The output
looks like this (fixed-width font required):

              3              {1..2,4..6}              {1..2,4..6}              [4..6]              {2,4..6}              {1..2,5}
              [1..2]              {1..3,5..6}              [1..3]              {2,5}              {1..3,5..6}              4
              [4..6]              [2..6]              [1..5]              [4..6]              [2..6]              {1..3,5}
              [1..2]              [5..6]              [4..5]              3              [4..6]              [1..2]
              [4..6]              [2..6]              [2..6]              1              [3..6]              {2..3,5}
              [4..5]              [1..5]              [1..5]              {2,4..5}              [1..5]              6

The problem can be seen in the first item in the second row.  In the
first row, the "3" is correctly placed, but beneath it the "[1..2]" is
in the wrong spot -- the "]" should be directly beneath the "3".  The
reason is that the first thing printed -- the "[" -- is padded, and the
rest of the range isn't.  That is, because the range is printed
piece-by-piece, only the first piece is padded.

I do not know the proper C++ solution, but it seems like this would
work.  The idea is to print the entire range "[1..2]" as one unit.  In
gecode/int/view/print.cc, I changed the print_view method to build up
the range in a stringstream and then print that at the end.  This fixes
the problem I saw.  There are other places (e.g. print_scale, and the
Bool versions) where this would need to be fixed too.

Is this the right way to do it?

  template <class View>
  inline static std::ostream&
  print_view(std::ostream& os, const View& x) {
    std::stringstream ss;
    if (x.assigned()) {
      ss << x.val();
    } else if (x.range()) {
      ss << '[' << x.min() << ".." << x.max() << ']';
    } else {
      ss << '{';
      ViewRanges<View> r(x);
      while (true) {
        if (r.min() == r.max()) {
          ss << r.min();
        } else {
          ss << r.min() << ".." << r.max();
        }
        ++r;
        if (!r()) break;
        ss << ',';
      }
      ss << '}';
    }
    return os << ss.str();
  }