How to define the "OStream-object" for Dump-Method (math_vector/math_Matrix) ???

Hello folks,

i want to print the output of a vector, i use ...

math_vector vec(1,3); // filled the vector, then i want to print the entries

math_Vector::Dump ... needs an Standard_OStream-object,

>>> void Dump((Standard_OStream& o)

Somehow system everytime crashes, when i try, like

filebuf fb;
fb.open("testfile.dat", ios:out);
ostream out_dat(&fb)

vec.Dump(fb) // system crashes, CAN ANYONE GIVE ME AN EXAMPLE HOW TO DECLARE A Standard_OStream object,

thanks in advance!
-Steven