Re: Fwd: C program and mkoctfile problem

[Cecconello]

The C++ wrapper with some comments 

/* Example on how to call a C function from Octave using mkoctfile and a C++
wrapper.
 
   In this example, the C function is defined in the file: simple.c
   The function "simple" takes two inputs of type int and returns their sum.
 
   The C++ wrapper is defined in the file: simple_wrap.cc

   The function and its wrapper are compiled by issuing the command:
       
       mkoctfile -o simple.oct simple_wrap.cpp simple.c
   
   Once compiled, the function is called from within Octave as any other
function:
   
       octave:19> [a, b, c] = simple(5,15);
       The function has 2 input arguments and 3 output arguments.
       Input a =  5
       Input b =  15
       The sum is 20

   Furhter calls to the function "simple" from within Octave after the
source codes have been recompiled
   must be proceed by the clear instructions as shown in the example below:
   
       octave:20> [a, b, c] = simple(5,15);
       warning: library /home/marco/Documents/C Programming Tests/simple.oct
not reloaded due to existing references
   
       octave:21> clear simple
       octave:22> [a, b, c] = simple(5,15);
       The function has 2 input arguments and 3 output arguments.
       Input a =  5
       Input b =  15
       The sum is 20
   
*/

// C++ header necessary for the mkoctfile
#include <octave/oct.h>

// Declare the C funtion "simple"
extern "C" int simple (int a, int b);

/* The macro DEFUN_DLD  creates a dynamically loaded function where:
   simple       is the name of the C function
   args         contains the input arguments of the C function
   nargout      is the number of output arguments of the C function
   string       the text that will displayed when issuing the command "help
simple" from within Octave
*/
DEFUN_DLD (simple, args, nargout, "Simple test of calling a C function from
Octave with a C++ wrapper")
{
  // Number of input arguments of the C function  
  int nargin = args.length();
  
  // Declare the array "retval" which contains the return values of the C++
wrapper function
  octave_value_list retval;
  
  // Declares the variables to which the input arguments to the C function
are passed to
  int a, b;
  
  // Declares the return variable of the C function
  int c;
  
  // Assign the values to the variables
  a = args(0).int_value();
  b = args(1).int_value();  
  
  // Call the C function and assing the returned variable to c
  c =  simple(a, b);

  // Some printout:
  octave_stdout << "The function has " << args.length () << " input
arguments and " << nargout << " output arguments.\n";  
  printf("Input a =  %d\n", a);
  printf("Input b =  %d\n", b);
  printf("The sum is %d\n", c);
  
  // Assign the C++ wrapper return values to retval
  retval(0) = a;
  retval(1) = b;
  retval(2) = c;
  
  // Return value
  return retval;
}


The C function: 

int simple (int a, int b)
{
    // Declare the variable of type int
    int c;

    // Assing the sum of the function input arguments to the variable
    c = a + b;

    // Return the sum
    return c;
}





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