Info Catalog octave: Cell Arrays in Oct-Files octave: Oct-Files octave: Sparse Matrices in Oct-Files

octave: Structures in Oct-Files

 
 A.1.5 Structures in Oct-Files
 -----------------------------
 
 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’.
 

Info Catalog octave: Cell Arrays in Oct-Files octave: Oct-Files octave: Sparse Matrices in Oct-Files