Fortran
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This page describes an example of how to call liboctave functions from a Fortran program. In the example we will load an Octave array from a file in Octave's native ASCII format, it consists of two steps:
- write a C++ function with a C compatible interface and C linkage that reads a variable from an Octave ASCII file - write Fortran code using the "iso_c_binding" intrinsic module to call the C++ function
C++ function
| Code: octave_file_io.cc: C++ function to load a matrix from an ASCII file in Octave native format |
#include <octave_file_io.h>
#include <octave/oct.h>
#include <octave/ov.h>
#include <fstream>
#include <ls-oct-ascii.h>
#include <octave/octave.h>
#include <octave/parse.h>
#include <octave/toplev.h>
#include <octave/load-save.h>
#include <octave/oct-map.h>
#include <cstring>
int octave_load (const char* filename, const char* varname, double** data, int* numel)
{
string_vector argv (1);
load_save_format format = LS_ASCII;
install_types ();
argv(0) = varname;
std::ios::openmode mode = std::ios::in | std::ios::binary;
std::string fname (filename);
std::ifstream file (fname.c_str (), mode);
octave_scalar_map m = do_load (file, fname, format, oct_mach_info::flt_fmt_unknown,
false, false, true, argv, 0, 1, 1).scalar_map_value ();
file.close ();
Array<double> M = m.contents (varname).array_value ();
if (error_state)
return -1;
*data = (double*) malloc (M.numel () * sizeof (double));
*numel = M.numel ();
memcpy (*data, M.fortran_vec (), *numel * sizeof (double));
return 0;
}
|
Header file
| Code: octave_file_io.h: header file with C interface to octave_file_io.cc |
#ifndef OCTAVE_FILE_IO_H
#define OCTAVE_FILE_IO_H
#ifdef __cplusplus
extern "C" {
#endif
int octave_load (const char* filename, const char* varname, double** data, int* numel);
#ifdef __cplusplus
}
#endif
#endif
|
Fortran Code
| Code: octave_file_io.cc: C++ function to load a matrix from an ASCII file in Octave native format |
program octave_file_io_example
use iso_c_binding
implicit none
interface
function octave_load (filename, varname, data, numel) bind(c, name="octave_load")
use iso_c_binding
implicit none
integer(c_int) :: octave_load
character(kind=c_char), intent(in) :: filename(*)
character(kind=c_char), intent(in) :: varname(*)
type(c_ptr), intent(out) :: data
integer(c_int), intent(out) :: numel
end function octave_load
end interface
integer(c_int) :: res
type(c_ptr) :: data
real(c_double), pointer :: fdata(:)
integer(c_int) :: numel
res = octave_load (c_char_'pippo.octxt' // c_null_char, c_char_'A' // c_null_char, data, numel)
call c_f_pointer (data, fdata, (/numel/))
write (*,*) fdata
end program octave_file_io_example
|
Compiling the code
mkoctfile -I. octave_file_io.cc mkoctfile -I. --mkoctfile --link-stand-alone octave_file_io_example.f90 octave_file_io.o -o octave_file_io_example