Fortran

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