Hello,

I'm trying to get Eigen to work with a custom scalar type. In general, this has been quite easy, just following the instructions on the site. I can easily cast from doubles to my type, manipulate, etc. Almost everything is gravy. However, I am at a loss for how to get

cout << M << endl;

to work when M is a matrix with my custom scalar type. I have defined operator<< for my type. I get error messages like so:

eigen/Eigen/src/Core/IO.h:138: error: no match for 'operator<<' in 'sstr << (+ m)->Eigen::Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::coeff [with _Scalar = etree, int _Rows = 10000, int _Cols = 1, int _Options = 2, int _MaxRows = 10000, int _MaxCols = 1](i, j)'

Any idea what I need to do to get this to work? Thanks in advance! (BTW, if any Eigen developers read this, the library is fantastic.)

If this helps, I find I can print my matrix by doing

cout << M.cast<double>() << endl;

which is pretty tolerable, but I guess less than ideal.

Hi,

you have to implement operator<< for your custom type, e.g.:

Code: Select all

std::ostream & operator<< (std::ostream & s, const CustomScalarType& x)
{
  s << double(x);
  return s;
}

Thanks for the reply.

Yes, I have implemented operator<< for my type. (In fact, my implementation is almost identical to yours.) So, I can print a scalar by doing

cout << a << endl;

but this doesn't work with an Eigen matrix of my scalar.

My guess was that I would need to specialize Eigen::Matrix's templated operator<< for my type or something like that, but I haven't been able to figure this out.

ok, but the compiler cannot find it, so:

1 - check that cout << m(0,0); works fine where m is an Eigen matrix with your scalar type

2 - check it works for stringstream:
std::stringstream sstr;
sstr << m(0,0);

3 - check twice the prototype of your operator<< (ostream, const ref, etc.)

4 - check your operator is defined before including Eigen.

If you still have issue could you please paste all error messages.

good luck

Thank you, thank you, thank you! Those were some great instructions.

I am embarased to say that the problem was that I forgot to declare my type const in operator<<. In any case, I think your help here will be useful to others in the future.