gcc/fortran/doc/gfortran/gnu-fortran-command-options/options-for-interoperability-with-other-languages.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. _interoperability-options:
   7
   8 Options for interoperability with other languages
   9 *************************************************
  10
  11 .. index:: c-prototypes, Generating C prototypes from Fortran BIND(C) enteties
  12
  13 .. option:: -fc-prototypes
  14
  15   This option will generate C prototypes from ``BIND(C)`` variable
  16   declarations, types and procedure interfaces and writes them to
  17   standard output.  ``ENUM`` is not yet supported.
  18
  19   The generated prototypes may need inclusion of an appropriate header,
  20   such as ``<stdint.h>`` or ``<stdlib.h>``.  For types which are
  21   not specified using the appropriate kind from the ``iso_c_binding``
  22   module, a warning is added as a comment to the code.
  23
  24   For function pointers, a pointer to a function returning ``int``
  25   without an explicit argument list is generated.
  26
  27   Example of use:
  28
  29   .. code-block:: shell-session
  30
  31     $ gfortran -fc-prototypes -fsyntax-only foo.f90 > foo.h
  32
  33   where the C code intended for interoperating with the Fortran code
  34   then  uses ``#include "foo.h"``.
  35
  36 .. index:: c-prototypes-external, Generating C prototypes from external procedures
  37
  38 .. option:: -fc-prototypes-external
  39
  40   This option will generate C prototypes from external functions and
  41   subroutines and write them to standard output.  This may be useful for
  42   making sure that C bindings to Fortran code are correct.  This option
  43   does not generate prototypes for ``BIND(C)`` procedures, use
  44   :option:`-fc-prototypes` for that.
  45
  46   The generated prototypes may need inclusion of an appropriate
  47   header, such as ``<stdint.h>`` or ``<stdlib.h>``.
  48
  49   This is primarily meant for legacy code to ensure that existing C
  50   bindings match what :command:`gfortran` emits.  The generated C
  51   prototypes should be correct for the current version of the compiler,
  52   but may not match what other compilers or earlier versions of
  53   :command:`gfortran` need.  For new developments, use of the
  54   ``BIND(C)`` features is recommended.
  55
  56   Example of use:
  57
  58   .. code-block:: shell-session
  59
  60     $ gfortran -fc-prototypes-external -fsyntax-only foo.f > foo.h
  61
  62   where the C code intended for interoperating with the Fortran code
  63   then  uses ``#include "foo.h"``.