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A structure in Octave is a map between a number of fields represented and their
values. The Standard Template Library map class is used, with the pair
consisting of a std::string and an Octave Cell variable.
A simple example demonstrating the use of structures within oct-files is
#include <octave/oct.h>
#include <octave/ov-struct.h>
DEFUN_DLD (structdemo, args, , "Struct Demo")
{
if (args.length () != 2)
print_usage ();
if (! args(0).is_map ())
error ("structdemo: ARG1 must be a struct");
octave_scalar_map arg0 = args(0).scalar_map_value ();
//octave_map arg0 = args(0).map_value ();
if (! args(1).is_string ())
error ("structdemo: ARG2 must be a character string");
std::string arg1 = args(1).string_value ();
octave_value tmp = arg0.contents (arg1);
//octave_value tmp = arg0.contents (arg1)(0);
if (! tmp.is_defined ())
error ("structdemo: struct does not have a field named '%s'\n",
arg1.c_str ());
octave_scalar_map st;
st.assign ("selected", tmp);
return octave_value (st);
}
An example of its use is
x.a = 1; x.b = "test"; x.c = [1, 2]; structdemo (x, "b") ⇒ selected = test
The example above specifically uses the octave_scalar_map class which is
for representing a single struct. For structure arrays, the octave_map
class is used instead. The commented code shows how the demo could be modified
to handle a structure array. In that case, the contents method returns
a Cell which may have more than one element. Therefore, to obtain the
underlying octave_value in the single struct example we would write
octave_value tmp = arg0.contents (arg1)(0);
where the trailing (0) is the () operator on the Cell
object. If this were a true structure array with multiple elements we could
iterate over the elements using the () operator.
Structures are a relatively complex data container and there are more functions
available in oct-map.h which make coding with them easier than relying
on just contents.
Next: Sparse Matrices in Oct-Files, Previous: Cell Arrays in Oct-Files, Up: Oct-Files [Contents][Index]