glib/docs/reference/gobject/glib-genmarshal.rst

.. _glib-genmarshal(1):
.. meta::
   :copyright: Copyright 2003 Matthias Clasen
   :copyright: Copyright 2005, 2012, 2013, 2016 Red Hat, Inc.
   :copyright: Copyright 2010 Christian Persch
   :copyright: Copyright 2017, 2019, 2020 Emmanuele Bassi
   :copyright: Copyright 2020 Centricular
   :license: LGPL-2.1-or-later
..
   This has to be duplicated from above to make it machine-readable by `reuse`:
   SPDX-FileCopyrightText: 2003 Matthias Clasen
   SPDX-FileCopyrightText: 2005, 2012, 2013, 2016 Red Hat, Inc.
   SPDX-FileCopyrightText: 2010 Christian Persch
   SPDX-FileCopyrightText: 2017, 2019, 2020 Emmanuele Bassi
   SPDX-FileCopyrightText: 2020 Centricular
   SPDX-License-Identifier: LGPL-2.1-or-later

===============
glib-genmarshal
===============

------------------------------------------------------
C code marshaller generation utility for GLib closures
------------------------------------------------------

SYNOPSIS
--------

|  **glib-genmarshal** [OPTION…] [FILE…]

DESCRIPTION
-----------

``glib-genmarshal`` is a small utility that generates C code marshallers for
callback functions of the GClosure mechanism in the GObject sublibrary of GLib.
The marshaller functions have a standard signature, they get passed in the
invoking closure, an array of value structures holding the callback function
parameters and a value structure for the return value of the callback. The
marshaller is then responsible to call the respective C code function of the
closure with all the parameters on the stack and to collect its return value.

``glib-genmarshal`` takes a list of marshallers to generate as input. The
marshaller list is either read from files passed as additional arguments
on the command line; or from standard input, by using ``-`` as the input file.

MARSHALLER LIST FORMAT
^^^^^^^^^^^^^^^^^^^^^^

The marshaller lists are processed line by line, a line can contain a comment in
the form of::

   # this is a comment

or a marshaller specification of the form::

   RTYPE:PTYPE
   RTYPE:PTYPE,PTYPE
   RTYPE:PTYPE,PTYPE,PTYPE
   …

The ``RTYPE`` part specifies the callback’s return type and the ``PTYPE``
instances right of the colon specify the callback’s parameter list, except for
the first and the last arguments which are always pointers.

PARAMETER TYPES
^^^^^^^^^^^^^^^

Currently, the following types are supported:

``VOID``

  Indicates no return type, or no extra parameters. If ``VOID`` is used as the
  parameter list, no additional parameters may be present.

``BOOLEAN``

  For boolean types (``gboolean``).

``CHAR``

  For signed char types (``gchar``).

``UCHAR``

  For unsigned char types (``guchar``).

``INT``

  For signed integer types (``gint``).

``UINT``

  For unsigned integer types (``guint``).

``LONG``

  For signed long integer types (``glong``).

``ULONG``

  For unsigned long integer types (``gulong``).

``INT64``

  For signed 64-bit integer types (``gint64``).

``UINT64``

  For unsigned 64-bit integer types (``guint64``).

``ENUM``

  For enumeration types (``gint``).

``FLAGS``

  For flag enumeration types (``guint``).

``FLOAT``

  For single-precision float types (``gfloat``).

``DOUBLE``

  For double-precision float types (``gdouble``).

``STRING``

  For string types (``gchar*``).

``BOXED``

  For boxed (anonymous but reference counted) types (``GBoxed*``).

``PARAM``

  For ``GParamSpec`` or derived types (``GParamSpec*``).

``POINTER``

  For anonymous pointer types (``gpointer``).

``OBJECT``

  For ``GObject`` or derived types (``GObject*``).

``VARIANT``

  For ``GVariant`` types (``GVariant*``).

``NONE``

  Deprecated alias for ``VOID``.

``BOOL``

  Deprecated alias for ``BOOLEAN``.

OPTIONS
-------

``--header``

  Generate header file contents of the marshallers. This option is mutually
  exclusive with the ``--body`` option.

``--body``

  Generate C code file contents of the marshallers. This option is mutually
  exclusive with the ``--header`` option.

``--prefix <PREFIX>``

  Specify marshaller prefix. The default prefix is ``g_cclosure_user_marshal``.

``--skip-source``

  Skip source location remarks in generated comments.

``--stdinc``

  Use the standard marshallers of the GObject library, and include
  ``glib-object.h`` in generated header files. This option is mutually exclusive
  with the ``--nostdinc`` option.

``--nostdinc``

  Do not use the standard marshallers of the GObject library, and skip the
  ``glib-object.h`` include directive in generated header files.
  This option is mutually exclusive with the ``--stdinc`` option.

``--internal``

  Mark generated functions as internal, using ``G_GNUC_INTERNAL``.

``-valist-marshallers``

  Generate ``valist`` marshallers, for use with
  ``g_signal_set_va_marshaller()``.

``-v``, ``--version``

  Print version information and exit.

``--g-fatal-warnings``

  Make warnings fatal. That is, exit immediately once a warning occurs.

``-h``, ``--help``

  Print brief help and exit.

``--output <FILE>``

  Write output to ``FILE`` instead of the standard output.

``--prototypes``

  Generate function prototypes before the function definition in the C source
  file, in order to avoid a ``missing-prototypes`` compiler warning. This option
  is only useful when using the ``--body`` option.

``--pragma-once``

  Use the ``once`` pragma instead of an old style header guard
  when generating the C header file. This option is only useful when using the
  ``--header`` option.

``--include-header <HEADER>``

  Adds a ``#include`` directive for the given file in the C source file. This
  option is only useful when using the ``--body`` option.

``-D <SYMBOL>[=<VALUE>]``

  Adds a ``#define`` C pre-processor directive for ``SYMBOL`` and its given
  ``VALUE``, or ``"1"`` if the value is unset. You can use this option multiple
  times; if you do, all the symbols will be defined in the same order given on
  the command line, before the symbols undefined using the ``-U`` option. This
  option is only useful when using the ``--body`` option.

``-U <SYMBOL>``

  Adds a ``#undef`` C pre-processor directive to undefine the given ``SYMBOL``.
  You can use this option multiple times; if you do, all the symbols will be
  undefined in the same order given on the command line, after the symbols
  defined using the ``-D`` option. This option is only useful when using the
  ``--body`` option.

``--quiet``

  Minimizes the output of ``glib-genmarshal``, by printing only warnings and
  errors. This option is mutually exclusive with the ``--verbose`` option.

``--verbose``

  Increases the verbosity of ``glib-genmarshal``, by printing debugging
  information. This option is mutually exclusive with the ``--quiet`` option.

USING GLIB-GENMARSHAL WITH MESON
--------------------------------

Meson supports generating closure marshallers using ``glib-genmarshal`` out of
the box in its ``gnome`` module.

In your ``meson.build`` file you will typically call the ``gnome.genmarshal()``
method with the source list of marshallers to generate::

   gnome = import('gnome')
   marshal_files = gnome.genmarshal('marshal',
     sources: 'marshal.list',
     internal: true,
   )

The ``marshal_files`` variable will contain an array of two elements in the
following order:

* a build target for the source file
* a build target for the header file

You should use the returned objects to provide a dependency on every other
build target that references the source or header file; for instance, if you
are using the source to build a library::

   mainlib = library('project',
     sources: project_sources + marshal_files,
     …
   )

Additionally, if you are including the generated header file inside a build
target that depends on the library you just built, you must ensure that the
internal dependency includes the generated header as a required source file::

   mainlib_dep = declare_dependency(sources: marshal_files[1], link_with: mainlib)

You should not include the generated source file as well, otherwise it will
be built separately for every target that depends on it, causing build
failures. To know more about why all this is required, please refer to the
`corresponding Meson FAQ entry <https://mesonbuild.com/FAQ.html#how-do-i-tell-meson-that-my-sources-use-generated-headers>`_.

For more information on how to use the method, see the
`Meson documentation <https://mesonbuild.com/Gnome-module.html#gnomegenmarshal>`_
for ``gnome.genmarshal()``.

USING GLIB-GENMARSHAL WITH AUTOTOOLS
------------------------------------

In order to use ``glib-genmarshal`` in your project when using Autotools as the
build system, you will first need to modify your ``configure.ac`` file to ensure
you find the appropriate command using ``pkg-config``, similarly as to how you
discover the compiler and linker flags for GLib::

   PKG_PROG_PKG_CONFIG([0.28])

   PKG_CHECK_VAR([GLIB_GENMARSHAL], [glib-2.0], [glib_genmarshal])

In your ``Makefile.am`` file you will typically need very simple rules to
generate the C files needed for the build::

   marshal.h: marshal.list
           $(AM_V_GEN)$(GLIB_GENMARSHAL) \
                   --header \
                   --output=$@ \
                   $<

   marshal.c: marshal.list marshal.h
           $(AM_V_GEN)$(GLIB_GENMARSHAL) \
                   --include-header=marshal.h \
                   --body \
                   --output=$@ \
                   $<

   BUILT_SOURCES += marshal.h marshal.c
   CLEANFILES += marshal.h marshal.c
   EXTRA_DIST += marshal.list

In the example above, the first rule generates the header file and depends on
a ``marshal.list`` file in order to regenerate the result in case the
marshallers list is updated. The second rule generates the source file for the
same ``marshal.list``, and includes the file generated by the header rule.

EXAMPLE
-------

To generate marshallers for the following callback functions::

   void   foo (gpointer data1,
               gpointer data2);
   void   bar (gpointer data1,
               gint     param1,
               gpointer data2);
   gfloat baz (gpointer data1,
               gboolean param1,
               guchar   param2,
               gpointer data2);

The ``marshaller.list`` file has to look like this::

   VOID:VOID
   VOID:INT
   FLOAT:BOOLEAN,UCHAR

and you call ``glib-genmarshal`` like this::

   glib-genmarshal --header marshaller.list > marshaller.h
   glib-genmarshal --body marshaller.list > marshaller.c

The generated marshallers have the arguments encoded in their function name.
For this particular list, they are::

   g_cclosure_user_marshal_VOID__VOID(...),
   g_cclosure_user_marshal_VOID__INT(...),
   g_cclosure_user_marshal_FLOAT__BOOLEAN_UCHAR(...).

They can be used directly for GClosures or be passed in as the
``GSignalCMarshaller c_marshaller`` argument upon creation of signals::

   GClosure *cc_foo, *cc_bar, *cc_baz;

   cc_foo = g_cclosure_new (NULL, foo, NULL);
   g_closure_set_marshal (cc_foo, g_cclosure_user_marshal_VOID__VOID);
   cc_bar = g_cclosure_new (NULL, bar, NULL);
   g_closure_set_marshal (cc_bar, g_cclosure_user_marshal_VOID__INT);
   cc_baz = g_cclosure_new (NULL, baz, NULL);
   g_closure_set_marshal (cc_baz, g_cclosure_user_marshal_FLOAT__BOOLEAN_UCHAR);

SEE ALSO
--------

`glib-mkenums(1) <man:glib-mkenums(1)>`_