Info on calling C from octave

[James Haefner]

Hi, I'm new to calling C (not C++) functions from octave and need some 
basic help:

(1) Is there a good tutorial that describes the uses/differences between
mex and mkoctfile and the general strategy for calling C functions in 
external libraries?

(2) In the mean time, can anyone explain these results from octave_2.9.6 
on a linux (ubuntu 6.10) machine:

The following C++ file (hello2oct.cc) works correctly when operated on 
by mkoctfile on the system command line:  "mkoctfile hello2oct.cc"
#include <octave/oct.h>
DEFUN_DLD (hello2oct, args, nargout,
       "Hello World Help String")
     {
       int nargin = args.length ();
       octave_stdout << "Hello World has " << nargin
             << " input arguments and "
             << nargout << " output arguments.\n";
       return octave_value_list ();
     }

The following C file (foobar.c) fails ("mkoctfile foobar.c") with the 
appended error messages:
#include <octave/oct.h>
DEFUN_DLD (foobar, args, nargout,
       "Hello World Help String")
     {
       return octave_value_list ();
     }

(same result if I remove the return line).

Errors:
In file included from /usr/include/octave-2.9.6/octave/mx-base.h:29,
                 from /usr/include/octave-2.9.6/octave/Matrix.h:31,
                 from /usr/include/octave-2.9.6/octave/oct.h:34,
                 from foobar.c:1:
/usr/include/octave-2.9.6/octave/MatrixType.h:26: error: expected '=', 
',', ';', 'asm' or '__attribute__' before 'Matrix'
/usr/include/octave-2.9.6/octave/MatrixType.h:27: error: expected '=', 
',', ';', 'asm' or '__attribute__' before 'ComplexMatrix'
/usr/include/octave-2.9.6/octave/MatrixType.h:28: error: expected '=', 
',', ';', 'asm' or '__attribute__' before 'SparseMatrix'
/usr/include/octave-2.9.6/octave/MatrixType.h:29: error: expected '=', 
',', ';', 'asm' or '__attribute__' before 'SparseComplexMatrix'
/
... followed by many similar lines

Obviously, I'm missing some fundamental concepts here, so any help will 
be appreciated.


Jim Haefner