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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-wrapping-hg-files"></a>The .hg and .ccg files</h2></div></div></div>
<p>The .hg and .ccg source files are very much like
.h and .cc C++ source files, but they contain extra macros, such as
<code class="function">_CLASS_GOBJECT()</code> and
<code class="function">_WRAP_METHOD()</code>, from which
<span class="command"><strong>gmmproc</strong></span> generates appropriate C++ source code,
usually at the same position in the header. Any additional C++ source
code will be copied verbatim into the corresponding
.h or .cc file.</p>
<p>A .hg file will typically include some headers
and then declare a class, using some macros to add API or behaviour to
this class. For instance, <span class="application">gtkmm</span>'s <code class="filename">button.hg</code> looks
roughly like this:
</p>
<pre class="programlisting">
#include <gtkmm/bin.h>
#include <gtkmm/activatable.h>
_DEFS(gtkmm,gtk)
_PINCLUDE(gtkmm/private/bin_p.h)
namespace Gtk
{
class Button
: public Bin,
public Activatable // Activatable is deprecated. Will be replaced at ABI break.
{
_CLASS_GTKOBJECT(Button,GtkButton,GTK_BUTTON,Gtk::Bin,GtkBin)
_IMPLEMENTS_INTERFACE(Activatable)
public:
_CTOR_DEFAULT
explicit Button(const Glib::ustring& label, bool mnemonic = false);
_WRAP_METHOD(void set_label(const Glib::ustring& label), gtk_button_set_label)
...
_WRAP_SIGNAL(void clicked(), "clicked")
...
_WRAP_PROPERTY("label", Glib::ustring)
};
} // namespace Gtk
</pre>
<p>
</p>
<p>The macros in this example do the following:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><code class="function">_DEFS()</code></span></dt>
<dd><p>Specifies the destination directory for generated sources, and the name of the main .defs file that <span class="command"><strong>gmmproc</strong></span> should parse.</p></dd>
<dt><span class="term"><code class="function">_PINCLUDE()</code></span></dt>
<dd><p>Tells <span class="command"><strong>gmmproc</strong></span> to include a header in the generated private/button_p.h file.</p></dd>
<dt><span class="term"><code class="function">_CLASS_GTKOBJECT()</code></span></dt>
<dd><p>Tells <span class="command"><strong>gmmproc</strong></span> to add some typedefs, constructors, and standard methods to this class, as appropriate when wrapping a widget.</p></dd>
<dt><span class="term"><code class="function">_IMPLEMENTS_INTERFACE()</code></span></dt>
<dd><p>Tells <span class="command"><strong>gmmproc</strong></span> to add initialization code for the interface.</p></dd>
<dt><span class="term"><code class="function">_CTOR_DEFAULT</code></span></dt>
<dd><p>Add a default constructor.</p></dd>
<dt><span class="term"><code class="function">_WRAP_METHOD()</code>,
<code class="function">_WRAP_SIGNAL()</code>,
<code class="function">_WRAP_PROPERTY()</code>, and
<code class="function">_WRAP_CHILD_PROPERTY()</code></span></dt>
<dd><p>Add methods to wrap parts of the C API.</p></dd>
</dl></div>
<p>
</p>
<p>The .h and .cc files will be generated from the .hg and .ccg files by
processing them with <span class="command"><strong>gmmproc</strong></span> like so, though this happens
automatically when using the above build structure:
</p>
<pre class="programlisting">
$ cd gtk/src
$ /usr/lib/glibmm-2.4/proc/gmmproc -I ../../tools/m4 --defs . button . ./../gtkmm
</pre>
<p>
</p>
<p>Notice that we provided <span class="command"><strong>gmmproc</strong></span> with the path to the
.m4 convert files, the path to the .defs file, the name of a .hg file, the
source directory, and the destination directory.</p>
<p>You should avoid including the C header from your C++ header, to avoid
polluting the global namespace, and to avoid exporting unnecessary public
API. But you will need to include the necessary C headers from your
.ccg file.</p>
<p>The macros are explained in more detail in the following sections.</p>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-m4-conversions"></a>m4 Conversions</h3></div></div></div>
<p>The macros that you use in the .hg and .ccg files often need to know how
to convert a C++ type to a C type, or vice-versa. gmmproc takes this information
from an .m4 file in your <code class="literal">tools/m4/</code> directory. This allows it
to call a C function in the implementation of your C++ method, passing the
appropriate parameters to that C functon. For instance, this
tells gmmproc how to convert a GtkTreeView pointer to a Gtk::TreeView pointer:
</p>
<pre class="programlisting">
_CONVERSION(`GtkTreeView*',`TreeView*',`Glib::wrap($3)')
</pre>
<p>
</p>
<p><code class="literal">$3</code> will be replaced by the parameter name when this
conversion is used by gmmproc.
</p>
<p>
Some extra macros make this easier and consistent. Look in gtkmm's .m4 files
for examples. For instance:
</p>
<pre class="programlisting">
_CONVERSION(`PrintSettings&',`GtkPrintSettings*',__FR2P)
_CONVERSION(`const PrintSettings&',`GtkPrintSettings*',__FCR2P)
_CONVERSION(`const Glib::RefPtr<Printer>&',`GtkPrinter*',__CONVERT_REFPTR_TO_P($3))
</pre>
<p>
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-m4-initializations"></a>m4 Initializations</h3></div></div></div>
<p>
Often when wrapping methods, it is desirable to store the return of the C
function in what is called an output parameter. In this case, the C++ method
returns <span class="type">void</span> but an output parameter in which to store the value
of the C function is included in the argument list of the C++ method.
gmmproc allows such functionality, but appropriate initialization macros must
be included to tell gmmproc how to initialize the C++ parameter from the
return of the C function.
</p>
<p>
For example, if there was a C function that returned a
<span class="type">GtkWidget*</span> and for some reason, instead of having the C++ method
also return the widget, it was desirable to have the C++ method place the
widget in a specified output parameter, an initialization macro such as the
following would be necessary:
</p>
<pre class="programlisting">
_INITIALIZATION(`Gtk::Widget&',`GtkWidget*',`$3 = Glib::wrap($4)')
</pre>
<p>
</p>
<p>
<code class="literal">$3</code> will be replaced by the output parameter name of the
C++ method and <code class="literal">$4</code> will be replaced by the return of the C
function when this initialization is used by gmmproc. For convenience,
<code class="literal">$1</code> will also be replaced by the C++ type without the
ampersand (&) and <code class="literal">$2</code> will be replaced by the C type.
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-class-macros"></a>Class macros</h3></div></div></div>
<p>The class macro declares the class itself and its relationship with the
underlying C type. It generates some internal constructors, the member
<code class="varname">gobject_</code>, typedefs, the <code class="function">gobj()</code>
accessors, type registration, and the <code class="function">Glib::wrap()</code>
method, among other things.</p>
<p>Other macros, such as <code class="function">_WRAP_METHOD()</code> and
<code class="function">_WRAP_SIGNAL()</code> may only be used after a call to a
<code class="function">_CLASS_*</code> macro.</p>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-gobject"></a>_CLASS_GOBJECT</h4></div></div></div>
<p>This macro declares a wrapper for a type that is derived from
<code class="classname">GObject</code>, but whose wrapper is not derived from
<code class="classname">Gtk::Object</code>.</p>
<p><code class="function">_CLASS_GOBJECT( C++ class, C class, C casting macro, C++ base class, C base class )</code></p>
<p>For instance, from <code class="filename">accelgroup.hg</code>:
</p>
<pre class="programlisting">
_CLASS_GOBJECT(AccelGroup, GtkAccelGroup, GTK_ACCEL_GROUP, Glib::Object, GObject)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-gtkobject"></a>_CLASS_GTKOBJECT</h4></div></div></div>
<p>This macro declares a wrapper for a type whose wrapper is derived from
<code class="classname">Gtk::Object</code>, such as a widget or dialog.</p>
<p><code class="function">_CLASS_GTKOBJECT( C++ class, C class, C casting macro, C++ base class, C base class )</code></p>
<p>For instance, from <code class="filename">button.hg</code>:
</p>
<pre class="programlisting">
_CLASS_GTKOBJECT(Button, GtkButton, GTK_BUTTON, Gtk::Bin, GtkBin)
</pre>
<p>
</p>
<p>You will typically use this macro when the class already derives from Gtk::Object. For instance, you will use it when wrapping a GTK+ Widget, because Gtk::Widget derives from Gtk::Object.</p>
<p>You might also derive non-widget classes from
<code class="classname">Gtk::Object</code> so they can be used without
<code class="classname">Glib::RefPtr</code>. For instance, they could then be
instantiated with <code class="function">Gtk::make_managed()</code> or on the stack
as a member variable. This is convenient, but you should use this only when
you are sure that true reference-counting is not needed. We consider it
useful for widgets.</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-boxedtype"></a>_CLASS_BOXEDTYPE</h4></div></div></div>
<p>This macro declares a wrapper for a non-<code class="classname">GObject</code>
struct, registered with
<code class="function">g_boxed_type_register_static()</code>.</p>
<p><code class="function">_CLASS_BOXEDTYPE( C++ class, C class, new function, copy function, free function )</code></p>
<p>For instance, from <code class="classname">Gdk::RGBA</code>:
</p>
<pre class="programlisting">
_CLASS_BOXEDTYPE(RGBA, GdkRGBA, NONE, gdk_rgba_copy, gdk_rgba_free)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-boxedtype-static"></a>_CLASS_BOXEDTYPE_STATIC</h4></div></div></div>
<p>This macro declares a wrapper for a simple assignable struct such as
<code class="classname">GdkRectangle</code>. It is similar to
<code class="function">_CLASS_BOXEDTYPE</code>, but the C struct is not allocated
dynamically.</p>
<p><code class="function">_CLASS_BOXEDTYPE_STATIC( C++ class, C class )</code></p>
<p>For instance, for <code class="classname">Gdk::Rectangle</code>:
</p>
<pre class="programlisting">
_CLASS_BOXEDTYPE_STATIC(Rectangle, GdkRectangle)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-opaque-copyable"></a>_CLASS_OPAQUE_COPYABLE</h4></div></div></div>
<p>This macro declares a wrapper for an opaque struct that has copy and free
functions. The new, copy and free functions will be used to instantiate the
default constructor, copy constructor and destructor.</p>
<p><code class="function">_CLASS_OPAQUE_COPYABLE( C++ class, C class, new function, copy function, free function )</code></p>
<p>For instance, from <code class="classname">Glib::Checksum</code>:
</p>
<pre class="programlisting">
_CLASS_OPAQUE_COPYABLE(Checksum, GChecksum, NONE, g_checksum_copy, g_checksum_free)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-opaque-refcounted"></a>_CLASS_OPAQUE_REFCOUNTED</h4></div></div></div>
<p>This macro declares a wrapper for a reference-counted opaque struct. The
C++ wrapper cannot be directly instantiated and can only be used with
<code class="classname">Glib::RefPtr</code>.</p>
<p><code class="function">_CLASS_OPAQUE_REFCOUNTED( C++ class, C class, new function, ref function, unref function )</code></p>
<p>For instance, for <code class="classname">Pango::Coverage</code>:
</p>
<pre class="programlisting">
_CLASS_OPAQUE_REFCOUNTED(Coverage, PangoCoverage, pango_coverage_new, pango_coverage_ref, pango_coverage_unref)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-generic"></a>_CLASS_GENERIC</h4></div></div></div>
<p>This macro can be used to wrap structs which don't fit into any
specialized category.</p>
<p><code class="function">_CLASS_GENERIC( C++ class, C class )</code></p>
<p>For instance, for <code class="classname">Pango::AttrIter</code>:
</p>
<pre class="programlisting">
_CLASS_GENERIC(AttrIter, PangoAttrIterator)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-class-interface"></a>_CLASS_INTERFACE</h4></div></div></div>
<p>This macro declares a wrapper for a type that is derived from
<code class="classname">GTypeInterface</code>.
</p>
<p><code class="function">_CLASS_INTERFACE( C++ class, C class, C casting macro, C interface struct, Base C++ class (optional), Base C class (optional) )</code></p>
<p>
For instance, from <code class="filename">celleditable.hg</code>:
</p>
<pre class="programlisting">
_CLASS_INTERFACE(CellEditable, GtkCellEditable, GTK_CELL_EDITABLE, GtkCellEditableIface)
</pre>
<p>
</p>
<p>Two extra parameters are optional, for the case that the interface derives from another interface,
which should be the case when the GInterface has another GInterface as a prerequisite.
For instance, from <code class="filename">loadableicon.hg</code>:
</p>
<pre class="programlisting">
_CLASS_INTERFACE(LoadableIcon, GLoadableIcon, G_LOADABLE_ICON, GLoadableIconIface, Icon, GIcon)
</pre>
<p>
</p>
</div>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-constructor-macros"></a>Constructor macros</h3></div></div></div>
<p>The <code class="function">_CTOR_DEFAULT()</code> and
<code class="function">_WRAP_CTOR()</code> macros add constructors, wrapping the
specified <code class="function">*_new()</code> C functions. These macros assume that
the C object has properties with the same names as the function parameters,
as is usually the case, so that it can supply the parameters directly to a
<code class="function">g_object_new()</code> call. These constructors never actually
call the <code class="function">*_new()</code> C functions,
because gtkmm must actually instantiate derived GTypes, and the
<code class="function">*_new()</code> C functions are meant only as convenience
functions for C programmers.</p>
<p>When using <code class="function">_CLASS_GOBJECT()</code>, the constructors should
be protected (rather than public) and each constructor should have a
corresponding <code class="function">_WRAP_CREATE()</code> in the public section.
This prevents the class from being instantiated without using a
<code class="classname">RefPtr</code>. For instance:
</p>
<pre class="programlisting">
class TextMark : public Glib::Object
{
_CLASS_GOBJECT(TextMark, GtkTextMark, GTK_TEXT_MARK, Glib::Object, GObject)
protected:
_WRAP_CTOR(TextMark(const Glib::ustring& name, bool left_gravity = true), gtk_text_mark_new)
public:
_WRAP_CREATE(const Glib::ustring& name, bool left_gravity = true)
</pre>
<p>
</p>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-ctor-default"></a>_CTOR_DEFAULT</h4></div></div></div>
<p>This macro creates a default constructor with no arguments.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-ctor"></a>_WRAP_CTOR</h4></div></div></div>
<p>This macro creates a constructor with arguments, equivalent to a
<code class="function">*_new()</code> C function. It won't actually call the
<code class="function">*_new()</code> function, but will simply create an equivalent
constructor with the same argument types. It takes a C++ constructor
signature, and a C function name.
</p>
<p>It also takes an optional extra argument:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">errthrow</span></dt>
<dd><p>This tells gmmproc that the C <code class="function">*_new()</code> has
a final GError** parameter which should be ignored.</p></dd>
</dl></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-ctor-manual"></a>Hand-coding constructors</h4></div></div></div>
<p>When a constructor must be partly hand written because, for instance, the
<code class="function">*_new()</code> C function's parameters do not correspond
directly to object properties, or because the <code class="function">*_new()</code> C
function does more than call <code class="function">g_object_new()</code>, the
<code class="function">_CONSTRUCT()</code> macro may be used in the
.ccg file to save some work. The <code class="function">_CONSTRUCT</code> macro takes
a series of property names and values. For instance, from
<code class="filename">button.ccg</code>:
</p>
<pre class="programlisting">
Button::Button(const Glib::ustring& label, bool mnemonic)
:
_CONSTRUCT("label", label.c_str(), "use_underline", gboolean(mnemonic))
{}
</pre>
<p>
</p>
</div>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-suppressing-macros"></a>Macros that suppress generation of some code</h3></div></div></div>
<p>Some macros suppress the generation of some code when they are used after
a <code class="function">_CLASS_*</code> macro. Some suppress the definition in the
generated .cc file, others suppress both the declaration in the .h file and
the definition in the .cc file.
</p>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-custom-default-ctor"></a>_CUSTOM_DEFAULT_CTOR</h4></div></div></div>
<p>Suppresses declaration and definition of default constructor in
<code class="function">_CLASS_BOXEDTYPE</code>, <code class="function">_CLASS_BOXEDTYPE_STATIC</code>
and <code class="function">_CLASS_OPAQUE_COPYABLE</code>.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-custom-ctor-cast"></a>_CUSTOM_CTOR_CAST</h4></div></div></div>
<p>Suppresses declaration and definition of the constructor that takes a pointer
to the wrapped C object in <code class="function">_CLASS_BOXEDTYPE</code> and
<code class="function">_CLASS_BOXEDTYPE_STATIC</code>.
</p>
<p>Suppresses definition of the constructor that takes a pointer to the
wrapped C object in <code class="function">_CLASS_GOBJECT</code>, <code class="function">_CLASS_GTKOBJECT</code>,
<code class="function">_CLASS_INTERFACE</code> and <code class="function">_CLASS_OPAQUE_COPYABLE</code>.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-custom-dtor"></a>_CUSTOM_DTOR</h4></div></div></div>
<p>Suppresses definition of destructor in
<code class="function">_CLASS_GOBJECT</code> and <code class="function">_CLASS_GTKOBJECT</code>.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-custom-move-operations"></a>_CUSTOM_MOVE_OPERATIONS</h4></div></div></div>
<p>Suppresses declaration and definition of move constructor and move
assignment operator in <code class="function">_CLASS_GOBJECT</code>.
</p>
<p>For example:
</p>
<pre class="programlisting">
class Derived : public Glib::Object
{
_CLASS_GOBJECT(Derived, GDerived, G_DERIVED, Glib::Object, GObject)
_CUSTOM_MOVE_OPERATIONS
public:
Derived(Derived&& src) noexcept;
Derived& operator=(Derived&& src) noexcept;
// ...
};
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-custom-wrap-new"></a>_CUSTOM_WRAP_NEW</h4></div></div></div>
<p>Suppresses definition of <code class="function">Glib::wrap_new()</code> function in
<code class="function">_CLASS_GOBJECT</code>.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-custom-wrap-function"></a>_CUSTOM_WRAP_FUNCTION</h4></div></div></div>
<p>Suppresses definition of <code class="function">Glib::wrap()</code> function in
<code class="function">_CLASS_GOBJECT</code> and <code class="function">_CLASS_GTKOBJECT</code>.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-no-wrap-function"></a>_NO_WRAP_FUNCTION</h4></div></div></div>
<p>Suppresses declaration and definition of <code class="function">Glib::wrap()</code>
function in <code class="function">_CLASS_GOBJECT</code>, <code class="function">_CLASS_BOXEDTYPE</code>,
<code class="function">_CLASS_BOXEDTYPE_STATIC</code>, <code class="function">_CLASS_OPAQUE_COPYABLE</code>,
<code class="function">_CLASS_INTERFACE</code> and <code class="function">_CLASS_GTKOBJECT</code>.
</p>
</div>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-method-macros"></a>Method macros</h3></div></div></div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-method"></a>_WRAP_METHOD</h4></div></div></div>
<p>This macro generates the C++ method to wrap a C function.</p>
<p><code class="function">_WRAP_METHOD( C++ method signature, C function name)</code></p>
<p>For instance, from <code class="filename">entry.hg</code>:
</p>
<pre class="programlisting">
_WRAP_METHOD(void set_text(const Glib::ustring& text), gtk_entry_set_text)
</pre>
<p>
</p>
<p>The C function (e.g. <code class="function">gtk_entry_set_text</code>) is described
more fully in the .defs file, and the <code class="filename">convert*.m4</code> files
contain the necessary conversion from the C++ parameter type to the C
parameter type. This macro also generates doxygen documentation comments
based on the <code class="filename">*_docs.xml</code> and
<code class="filename">*_docs_override.xml</code> files.</p>
<p>There are some optional extra arguments:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">refreturn</span></dt>
<dd><p>Do an extra <code class="function">reference()</code> on the return value,
in case the C function does not provide a reference.</p></dd>
<dt><span class="term">errthrow</span></dt>
<dd><p>Use the last GError** parameter of the C function to
throw an exception.</p></dd>
<dt><span class="term">deprecated ["<text>"]</span></dt>
<dd><p>Puts the generated code in #ifdef blocks. Text about the
deprecation can be specified as an optional
parameter.</p></dd>
<dt><span class="term">constversion</span></dt>
<dd><p>Just call the non-const version of the same function,
instead of generating almost duplicate code.</p></dd>
<dt><span class="term">newin "<version>"</span></dt>
<dd><p>Adds a @newin Doxygen command to the documentation, or replaces
the @newin command generated from the C documentation.</p></dd>
<dt><span class="term">ifdef <identifier></span></dt>
<dd><p>Puts the generated code in #ifdef blocks.</p></dd>
<dt><span class="term">slot_name <parameter_name></span></dt>
<dd><p>Specifies the name of the slot parameter of the method, if it
has one. This enables <span class="command"><strong>gmmproc</strong></span> to generate code
to copy the slot and pass the copy on to the C function in its
final <code class="literal">gpointer user_data</code> parameter. The
<code class="literal">slot_callback</code> option must also be used to
specify the name of the glue callback function to also pass on to
the C function.</p></dd>
<dt><span class="term">slot_callback <function_name></span></dt>
<dd><p>Used in conjunction with the <code class="literal">slot_name</code>
option to specify the name of the glue callback function that
handles extracting the slot and then calling it. The address of
this callback is also passed on to the C function that the method
wraps.</p></dd>
<dt><span class="term">no_slot_copy</span></dt>
<dd><p>Tells <span class="command"><strong>gmmproc</strong></span> not to pass a copy of the slot
to the C function, if the method has one. Instead the slot itself
is passed. The slot parameter name and the glue callback function
must have been specified with the <code class="literal">slot_name</code> and
<code class="literal">slot_callback</code> options respectively.</p></dd>
</dl></div>
<p>
</p>
<p>Selecting which C++ types should be used is also important when wrapping
C API. Though it's usually obvious what C++ types should be used in the C++
method, here are some hints:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>Objects used via <code class="classname">RefPtr</code>: Pass the
<code class="classname">RefPtr</code> as a const reference. For instance,
<code class="code">const Glib::RefPtr<Gtk::FileFilter>&
filter</code>.</p></li>
<li class="listitem"><p>Const Objects used via <code class="classname">RefPtr</code>: If the
object should not be changed by the function, then make sure that
the object is const, even if the <code class="classname">RefPtr</code> is
already const. For instance, <code class="code">const Glib::RefPtr<const
Gtk::FileFilter>& filter</code>.</p></li>
<li class="listitem"><p>Wrapping <code class="classname">GList*</code> and
<code class="classname">GSList*</code> parameters: First, you need to discover
what objects are contained in the list's data field for each item,
usually by reading the documentation for the C function. The list can
then be wrapped by a <code class="classname">std::vector</code> type.
For instance, <code class="code">std::vector<
Glib::RefPtr<Gdk::Pixbuf> ></code>.
You may need to define a Traits type to specify how the C
and C++ types should be converted.</p></li>
<li class="listitem">
<p>Wrapping <code class="classname">GList*</code> and
<code class="classname">GSList*</code> return types: You must discover whether
the caller should free the list and whether it should release the items
in the list, again by reading the documentation of the C function. With
this information you can choose the ownership (none, shallow or deep)
for the m4 conversion rule, which you should probably put directly into
the .hg file because the ownership depends on the
function rather than the type. For instance:
</p>
<pre class="programlisting">#m4 _CONVERSION(`GSList*',`std::vector<Widget*>',`Glib::SListHandler<Widget*>::slist_to_vector($3, Glib::OWNERSHIP_SHALLOW)')</pre>
</li>
</ul></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-method-docs-only"></a>_WRAP_METHOD_DOCS_ONLY</h4></div></div></div>
<p>This macro is like <code class="function">_WRAP_METHOD()</code>, but it generates
only the documentation for a C++ method that wraps a C function. Use this
when you must hand-code the method, but you want to use the documentation
that would be generated if the method was generated.</p>
<p><code class="function">_WRAP_METHOD_DOCS_ONLY(C function name)</code></p>
<p>For instance, from <code class="filename">container.hg</code>:
</p>
<pre class="programlisting">
_WRAP_METHOD_DOCS_ONLY(gtk_container_remove)
</pre>
<p>
</p>
<p>There are some optional extra arguments:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">errthrow</span></dt>
<dd><p>Excludes documentation of the last GError** parameter of
the C function.</p></dd>
<dt><span class="term">newin "<version>"</span></dt>
<dd><p>Adds a @newin Doxygen command to the documentation, or replaces
the @newin command generated from the C documentation.</p></dd>
</dl></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-ignore"></a>_IGNORE, _IGNORE_SIGNAL, _IGNORE_PROPERTY, _IGNORE_CHILD_PROPERTY</h4></div></div></div>
<p><span class="command"><strong>gmmproc</strong></span> will warn you on stdout about functions, signals,
properties and child properties that you have forgotten to wrap, helping to
ensure that you are wrapping the complete API. But if you don't want to wrap
some functions, signals, properties or child properties, or if you chose
to hand-code some methods then you can use the _IGNORE(), _IGNORE_SIGNAL(),
_IGNORE_PROPERTY() or _IGNORE_CHILD_PROPERTY() macro to make
<span class="command"><strong>gmmproc</strong></span> stop complaining.</p>
<p>
</p>
<div class="literallayout"><p><code class="function">_IGNORE(C function name 1, C function name 2, etc)<br>
_IGNORE_SIGNAL(C signal name 1, C signal name 2, etc)<br>
_IGNORE_PROPERTY(C property name 1, C property name 2, etc)<br>
_IGNORE_CHILD_PROPERTY(C child property name 1, C child property name 2, etc)</code></p></div>
<p>
</p>
<p>For instance, from <code class="filename">flowbox.hg</code>:
</p>
<pre class="programlisting">
_IGNORE(gtk_flow_box_set_filter_func, gtk_flow_box_set_sort_func)
_IGNORE_SIGNAL(activate-cursor-child, toggle-cursor-child, move-cursor)
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-signal"></a>_WRAP_SIGNAL</h4></div></div></div>
<p>This macro generates the C++ libsigc++-style signal to wrap a C GObject
signal. It actually generates a public accessor method, such as
<code class="function">signal_clicked()</code>, which returns a proxy object.
<span class="command"><strong>gmmproc</strong></span> uses the .defs file to discover the C parameter
types and the .m4 convert files to discover appropriate type
conversions.</p>
<p><code class="function">_WRAP_SIGNAL( C++ signal handler signature, C signal name)</code></p>
<p>For instance, from <code class="filename">button.hg</code>:
</p>
<pre class="programlisting">
_WRAP_SIGNAL(void clicked(),"clicked")
</pre>
<p>
</p>
<p>Signals usually have function pointers in the GTK struct, with a
corresponding enum value and a <code class="function">g_signal_new()</code> in the
.c file.</p>
<p>There are some optional extra arguments:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">no_default_handler</span></dt>
<dd><p>Do not generate an <code class="function">on_something()</code> virtual
method to allow easy overriding of the default signal handler.
Use this when adding a signal with a default signal handler
would break the ABI by increasing the size of the class's
virtual function table.</p></dd>
<dt><span class="term">custom_default_handler</span></dt>
<dd><p>Generate a declaration of the <code class="function">on_something()</code>
virtual method in the <code class="filename">.h</code> file, but do not
generate a definition in the <code class="filename">.cc</code> file.
Use this when you must generate the definition by hand.</p></dd>
<dt><span class="term">custom_c_callback</span></dt>
<dd><p>Do not generate a C callback function for the signal.
Use this when you must generate the callback function by hand.</p></dd>
<dt><span class="term">refreturn</span></dt>
<dd><p>Do an extra <code class="function">reference()</code> on the return value
of the <code class="function">on_something()</code> virtual method, in
case the C function does not provide a reference.</p></dd>
<dt><span class="term">deprecated ["<text>"]</span></dt>
<dd><p>Puts the generated code in #ifdef blocks. Text about the
deprecation can be specified as an optional parameter.</p></dd>
<dt><span class="term">newin "<version>"</span></dt>
<dd><p>Adds a @newin Doxygen command to the documentation, or replaces
the @newin command generated from the C documentation.</p></dd>
<dt><span class="term">ifdef <identifier></span></dt>
<dd><p>Puts the generated code in #ifdef blocks.</p></dd>
<dt><span class="term">exception_handler <method_name></span></dt>
<dd><p>Allows to use custom exception handler instead of default one.
Exception might be rethrown by user-defined handler, and it will be
caught by default handler.</p></dd>
<dt><span class="term">detail_name <parameter_name></span></dt>
<dd><p>Adds a <span class="type">const Glib::ustring&</span> parameter to the
<code class="methodname">signal_something()</code> method. Use it, if the signal
accepts a detailed signal name, i.e. if the underlying C code registers
the signal with the <code class="literal">G_SIGNAL_DETAILED</code> flag.</p></dd>
<dt><span class="term">two_signal_methods</span></dt>
<dd><p>Used in conjunction with the <code class="literal">detail_name</code>
option to generate two <code class="methodname">signal_something()</code>
methods, one without a parameter and one with a parameter without
a default value. With only the <code class="literal">detail_name</code> option
one method is generated, with a parameter with default value.
Use the <code class="literal">two_signal_methods</code> option, if it's
necessary in order to preserve ABI.</p></dd>
</dl></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-property"></a>_WRAP_PROPERTY</h4></div></div></div>
<p>This macro generates the C++ method to wrap a C GObject property. You must
specify the property name and the wanted C++ type for the property. <span class="command"><strong>gmmproc</strong></span>
uses the .defs file to discover the C type and the .m4 convert files to
discover appropriate type conversions.</p>
<p><code class="function">_WRAP_PROPERTY(C property name, C++ type)</code></p>
<p>For instance, from <code class="filename">button.hg</code>:
</p>
<pre class="programlisting">
_WRAP_PROPERTY("label", Glib::ustring)
</pre>
<p>
</p>
<p>There are some optional extra arguments:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">deprecated ["<text>"]</span></dt>
<dd><p>Puts the generated code in #ifdef blocks. Text about the
deprecation can be specified as an optional parameter.</p></dd>
<dt><span class="term">newin "<version>"</span></dt>
<dd><p>Adds a @newin Doxygen command to the documentation, or replaces
the @newin command generated from the C documentation.</p></dd>
</dl></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-vfunc"></a>_WRAP_VFUNC</h4></div></div></div>
<p>This macro generates the C++ method to wrap a virtual C function.</p>
<p><code class="function">_WRAP_VFUNC( C++ method signature, C function name)</code></p>
<p>For instance, from <code class="filename">widget.hg</code>:
</p>
<pre class="programlisting">
_WRAP_VFUNC(SizeRequestMode get_request_mode() const, get_request_mode)
</pre>
<p>
</p>
<p>The C function (e.g. <code class="function">get_request_mode</code>) is described
more fully in the <code class="filename">*_vfuncs.defs</code> file, and the
<code class="filename">convert*.m4</code> files contain the necessary conversion from
the C++ parameter type to the C parameter type. Conversions can also be
written in the .hg file. Virtual functions often require special conversions
that are best kept local to the .hg file where they are used.</p>
<p>There are some optional extra arguments:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">refreturn</span></dt>
<dd><p>Do an extra <code class="function">reference()</code> on the return value
of the <code class="function">something_vfunc()</code> function,
in case the virtual C function does not provide a reference.</p></dd>
<dt><span class="term">refreturn_ctype</span></dt>
<dd><p>Do an extra <code class="function">reference()</code> on the return value
of an overridden <code class="function">something_vfunc()</code> function
in the C callback function, in case the calling C function
expects it to provide a reference.</p></dd>
<dt><span class="term">keep_return</span></dt>
<dd><p>Keep a copy of the return value in the C callback function,
in case the calling C function does not expect to get its own
reference.</p></dd>
<dt><span class="term">errthrow</span></dt>
<dd><p>Use the last GError** parameter of the C virtual function (if
there is one) to throw an exception.</p></dd>
<dt><span class="term">custom_vfunc</span></dt>
<dd><p>Do not generate a definition of the vfunc in the
<code class="filename">.cc</code> file. Use this when you must generate
the vfunc by hand.</p></dd>
<dt><span class="term">custom_vfunc_callback</span></dt>
<dd><p>Do not generate a C callback function for the vfunc.
Use this when you must generate the callback function by hand.</p></dd>
<dt><span class="term">ifdef <identifier></span></dt>
<dd><p>Puts the generated code in #ifdef blocks.</p></dd>
<dt><span class="term">slot_name <parameter_name></span></dt>
<dd><p>Specifies the name of the slot parameter of the method, if it
has one. This enables <span class="command"><strong>gmmproc</strong></span> to generate code
to copy the slot and pass the copy on to the C function in its
final <code class="literal">gpointer user_data</code> parameter. The
<code class="literal">slot_callback</code> option must also be used to
specify the name of the glue callback function to also pass on to
the C function.</p></dd>
<dt><span class="term">slot_callback <function_name></span></dt>
<dd><p>Used in conjunction with the <code class="literal">slot_name</code>
option to specify the name of the glue callback function that
handles extracting the slot and then calling it. The address of
this callback is also passed on to the C function that the method
wraps.</p></dd>
<dt><span class="term">no_slot_copy</span></dt>
<dd><p>Tells <span class="command"><strong>gmmproc</strong></span> not to pass a copy of the slot
to the C function, if the method has one. Instead the slot itself
is passed. The slot parameter name and the glue callback function
must have been specified with the <code class="literal">slot_name</code> and
<code class="literal">slot_callback</code> options respectively.</p></dd>
<dt><span class="term">return_value <value></span></dt>
<dd><p>Defines a non-default return value.</p></dd>
<dt><span class="term">err_return_value <value></span></dt>
<dd><p>Defines a non-default return value, used only if the C++
<code class="function">something_vfunc()</code> function throws an exception
which is propagated to the C callback function. If return_value is
specified, but err_return_value is not, then return_value is used
also when an exception is propagated.</p></dd>
<dt><span class="term">exception_handler <method_name></span></dt>
<dd><p>Allows to use custom exception handler instead of default one.
Exception might be rethrown by user-defined handler, and it will be
caught by default handler.</p></dd>
</dl></div>
<p>
</p>
<p>A rule to which there may be exceptions: If the virtual C function returns
a pointer to an object derived from <code class="classname">GObject</code>, i.e. a
reference-counted object, then the virtual C++ function shall return a
<code class="classname">Glib::RefPtr<></code> object. One of the extra
arguments <em class="parameter"><code>refreturn</code></em> or
<em class="parameter"><code>refreturn_ctype</code></em> is required.</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-child-property"></a>_WRAP_CHILD_PROPERTY</h4></div></div></div>
<p>This macro generates the C++ method to wrap a GtkContainer child property.
(See <a class="ulink" href="https://developer.gnome.org/gtk3/stable/GtkContainer.html" target="_top">
GtkContainer</a> for more information about child properties).
Similarly to _WRAP_PROPERTY, you must specify the property name and the
wanted C++ type for the property. <span class="command"><strong>gmmproc</strong></span> uses the .defs
file to discover the C type and the .m4 convert files to discover
appropriate type conversions.</p>
<p><code class="function">_WRAP_CHILD_PROPERTY(C child property name, C++ type)</code></p>
<p>For instance, from <code class="filename">notebook.hg</code>:
</p>
<pre class="programlisting">
_WRAP_CHILD_PROPERTY("tab-expand", bool)
</pre>
<p>
</p>
<p>_WRAP_CHILD_PROPERTY() accepts the same optional arguments as _WRAP_PROPERTY().
</p>
</div>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-other-macros"></a>Other macros</h3></div></div></div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-implements-interface"></a>_IMPLEMENTS_INTERFACE</h4></div></div></div>
<p>This macro generates initialization code for the interface.</p>
<p><code class="function">_IMPLEMENTS_INTERFACE(C++ interface name)</code></p>
<p>For instance, from <code class="filename">grid.hg</code>:
</p>
<pre class="programlisting">
_IMPLEMENTS_INTERFACE(Orientable)
</pre>
<p>
</p>
<p>There is one optional extra argument:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">ifdef <identifier></span></dt>
<dd><p>Puts the generated code in #ifdef blocks.</p></dd>
</dl></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-enum"></a>_WRAP_ENUM</h4></div></div></div>
<p>This macro generates a C++ enum to wrap a C enum. You must specify the desired C++ name and
the name of the underlying C enum.</p>
<p>For instance, from <code class="filename">enums.hg</code>:
</p>
<pre class="programlisting">
_WRAP_ENUM(WindowType, GtkWindowType)
</pre>
<p>
</p>
<p>There are some optional extra arguments:
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">NO_GTYPE</span></dt>
<dd>
<p>Use this option, if the enum is not a <code class="classname">GType</code>.
This is the case when there is no <code class="function">*_get_type()</code>
function for the C enum, but be careful that you don't just need to
include an extra header for that function. You should also file a bug
against the C API, because all enums should be registered as GTypes.</p>
<p>For example, from <code class="filename">icontheme.hg</code>:
</p>
<pre class="programlisting">
_WRAP_ENUM(IconLookupFlags, GtkIconLookupFlags, NO_GTYPE)
</pre>
<p>
</p>
</dd>
<dt><span class="term">s#<from>#<to>#</span></dt>
<dd>
<p>Substitutes (part of) the name of one or more enum constants.
You can add any number of substitutions.</p>
<p>For example, from <code class="filename">iochannel.hg</code> in glibmm:
</p>
<pre class="programlisting">
_WRAP_ENUM(SeekType, GSeekType, NO_GTYPE, s#^SEEK_#SEEK_TYPE_#)
</pre>
<p>
</p>
</dd>
<dt><span class="term">deprecated ["<text>"]</span></dt>
<dd><p>Puts the generated code in #ifdef blocks. Text about the
deprecation can be specified as an optional parameter.</p></dd>
<dt><span class="term">newin "<version>"</span></dt>
<dd><p>Adds a @newin Doxygen command to the documentation, or replaces
the @newin command generated from the C documentation.</p></dd>
</dl></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-enum-docs-only"></a>_WRAP_ENUM_DOCS_ONLY</h4></div></div></div>
<p>This macro just generates a Doxygen documentationn block for the enum.
This is useful for enums that can't be wrapped with
<code class="function">_WRAP_ENUM()</code> because they are complexly defined (maybe
using C macros) but including the generated enum documentation is still
desired. It is used with the same syntax as
<code class="function">_WRAP_ENUM()</code> and also process the same options (though
NO_GTYPE is just ignored because it makes no difference when just generating
the enum's documentation).
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-wrap-gerror"></a>_WRAP_GERROR</h4></div></div></div>
<p>This macro generates a C++ exception class, derived from Glib::Error, with
a Code enum and a code() method. You must specify the desired C++ name, the name
of the corresponding C enum, and the prefix for the C enum values.</p>
<p>This exception can then be thrown by methods which are generated from
_WRAP_METHOD() with the errthrow option.</p>
<p>For instance, from <code class="filename">pixbuf.hg</code>:
</p>
<pre class="programlisting">
_WRAP_GERROR(PixbufError, GdkPixbufError, GDK_PIXBUF_ERROR)
</pre>
<p>
</p>
<p>_WRAP_GERROR() accepts the same optional arguments as _WRAP_ENUM().</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-member-set-get"></a>_MEMBER_GET / _MEMBER_SET</h4></div></div></div>
<p>
Use these macros if you're wrapping a simple struct or boxed type that provides
direct access to its data members, to create getters and setters for the data members.
</p>
<p><code class="function">_MEMBER_GET(C++ name, C name, C++ type, C type)</code></p>
<p><code class="function">_MEMBER_SET(C++ name, C name, C++ type, C type)</code></p>
<p>
For example, in <code class="filename">rectangle.hg</code>:
</p>
<pre class="programlisting">_MEMBER_GET(x, x, int, int)</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-member-get-set-ptr"></a>_MEMBER_GET_PTR / _MEMBER_SET_PTR</h4></div></div></div>
<p>
Use these macros to automatically provide getters and setters for a data
member that is a pointer type. For the getter function, it will
create two methods, one const and one non-const.
</p>
<p><code class="function">_MEMBER_GET_PTR(C++ name, C name, C++ type, C type)</code></p>
<p><code class="function">_MEMBER_SET_PTR(C++ name, C name, C++ type, C type)</code></p>
<p>For example, for <code class="classname">Pango::Analysis</code> in <code class="filename">item.hg</code>:
</p>
<pre class="programlisting">
// _MEMBER_GET_PTR(engine_lang, lang_engine, EngineLang*, PangoEngineLang*)
// It's just a comment. It's difficult to find a real-world example.
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-member-get-set-gobject"></a>_MEMBER_GET_GOBJECT / _MEMBER_SET_GOBJECT</h4></div></div></div>
<p>
Use these macros to provide getters and setters for a data member that is a
<code class="classname">GObject</code> type that must be referenced before being
returned.
</p>
<p><code class="function">_MEMBER_GET_GOBJECT(C++ name, C name, C++ type, C type)</code></p>
<p><code class="function">_MEMBER_SET_GOBJECT(C++ name, C name, C++ type, C type)</code></p>
<p>For example, in Pangomm, <code class="filename">layoutline.hg</code>:
</p>
<pre class="programlisting">
_MEMBER_GET_GOBJECT(layout, layout, Pango::Layout, PangoLayout*)
</pre>
<p>
</p>
</div>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-parameter-processing"></a>gmmproc Parameter Processing</h3></div></div></div>
<p><span class="command"><strong>gmmproc</strong></span> allows processing the parameters in a method
signature for the macros that process method signatures (like
<code class="function">_WRAP_METHOD()</code>, <code class="function">_WRAP_CTOR()</code> and
<code class="function">_WRAP_CREATE()</code>) in a variety of ways:
</p>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-parameter-reordering"></a>Parameter Reordering</h4></div></div></div>
<p>
For all the macros that process method signatures, it is possible to
specify a different order for the C++ parameters than the existing order
in the C function, virtual function or signal. For example, say that the
following C function were being wrapped as a C++ method for the
<code class="classname">Gtk::Widget</code> class:
</p>
<pre class="programlisting">
void gtk_widget_set_device_events(GtkWidget* widget, GdkDevice* device,
GdkEventMask events);
</pre>
<p>
However, changing the order of the C++ method's two parameters is
necessary. Something like the following would wrap the function as a C++
method with a different order for the two parameters:
</p>
<pre class="programlisting">
_WRAP_METHOD(void set_device_events(Gdk::EventMask events{events},
const Glib::RefPtr<const Gdk::Device>& device{device}),
gtk_widget_set_device_events)
</pre>
<p>
The <code class="literal">{c_param_name}</code> following the method parameter
names tells <span class="command"><strong>gmmproc</strong></span> to map the C++ parameter to the
specified C parameter within the <code class="literal">{}</code>. Since the C++
parameter names correspond to the C ones, the above could be re-written
as:
</p>
<pre class="programlisting">
_WRAP_METHOD(void set_device_events(Gdk::EventMask events{.}, const
Glib::RefPtr<const Gdk::Device>& device{.}),
gtk_widget_set_device_events)
</pre>
<p>
</p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="icons/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
Please note that when reordering parameters for a
<code class="function">_WRAP_SIGNAL()</code> method signature, the C parameter
names would always be <code class="literal">p0</code>, <code class="literal">p1</code>,
etc. because the <code class="filename">generate_extra_defs</code> utility uses those
parameter names no matter what the C API's parameter names may be.
It's how the utility is written presently.
</p></td></tr>
</table></div>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-optional-parameter-processing"></a>Optional Parameter Processing</h4></div></div></div>
<p>
For all macros processing method signatures except
<code class="function">_WRAP_SIGNAL()</code> and
<code class="function">_WRAP_VFUNC()</code> it is also possible to make the
parameters optional so that extra C++ methods are generated without the
specified optional parameter. For example, say that the following
<code class="function">*_new()</code> function were being wrapped as a constructor
in the <code class="classname">Gtk::ToolButton</code> class:
</p>
<pre class="programlisting">
GtkToolItem* gtk_tool_button_new(GtkWidget* icon_widget, const gchar*
label);
</pre>
<p>
Also, say that the C API allowed NULL for the function's
<em class="parameter"><code>label</code></em> parameter so that that parameter is optional.
It would be possible to have <span class="command"><strong>gmmproc</strong></span> generate the
original constructor (with all the parameters) along with an additional
constructor without that optional parameter by appending a
<code class="literal">{?}</code> to the parameter name like so:
</p>
<pre class="programlisting">
_WRAP_CTOR(ToolButton(Widget& icon_widget, const Glib::ustring&
label{?}), gtk_tool_button_new)
</pre>
<p>
In this case, two constructors would be generated: One with the optional
parameter and one without it.
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-output-parameter-processing"></a>Output Parameter Processing</h4></div></div></div>
<p>
With <code class="function">_WRAP_METHOD()</code> it is also possible for the
return of the wrapped C function (if it has one) to be placed in an
output parameter of the C++ method instead of having the C++ method also
return a value like the C function does. To do that, simply include the
output parameter in the C++ method parameter list appending a
<code class="literal">{OUT}</code> to the output parameter name. For example, if
<code class="function">gtk_widget_get_request_mode()</code> is declared as the
following:
</p>
<pre class="programlisting">
GtkSizeRequestMode gtk_widget_get_request_mode(GtkWidget* widget);
</pre>
<p>
And having the C++ method set an output parameter is desired instead of
returning a <span class="type">SizeRequestMode</span>, something like the following
could be used:
</p>
<pre class="programlisting">
_WRAP_METHOD(void get_request_mode(SizeRequestMode& mode{OUT})
const, gtk_widget_get_request_mode)
</pre>
<p>
The <code class="literal">{OUT}</code> appended to the name of the
<em class="parameter"><code>mode</code></em> output parameter tells
<span class="command"><strong>gmmproc</strong></span> to place the return of the C function in that
output parameter. In this case, however, a necessary initialization
macro like the following would also have to be specified:
</p>
<pre class="programlisting">
_INITIALIZATION(`SizeRequestMode&',`GtkSizeRequestMode',`$3 =
(SizeRequestMode)($4)')
</pre>
<p>
Which could also be written as:
</p>
<pre class="programlisting">
_INITIALIZATION(`SizeRequestMode&',`GtkSizeRequestMode',`$3 =
($1)($4)')
</pre>
<p>
</p>
<p>
<code class="function">_WRAP_METHOD()</code> also supports setting C++ output
parameters from C output parameters if the C function being wrapped has
any. Suppose, for example, that we want to wrap the following C function
that returns a value in its C output parameter
<em class="parameter"><code>rect</code></em>:
</p>
<pre class="programlisting">
gboolean gtk_icon_view_get_cell_rect(GtkIconView* icon_view,
GtkTreePath* path, GtkCellRenderer* cell, GdkRectangle* rect);
</pre>
<p>
To have <span class="command"><strong>gmmproc</strong></span> place the value returned in the C++
<em class="parameter"><code>rect</code></em> output parameter, something like the
following <code class="function">_WRAP_METHOD()</code> directive could be used:
</p>
<pre class="programlisting">
_WRAP_METHOD(bool get_cell_rect(const TreeModel::Path& path, const
CellRenderer& cell, Gdk::Rectangle& rect{>>}) const,
gtk_icon_view_get_cell_rect)
</pre>
<p>
The <code class="literal">{>>}</code> following the <em class="parameter"><code>rect</code></em>
parameter name indicates that the C++ output parameter should be set from
the value returned in the C parameter from the C function.
<span class="command"><strong>gmmproc</strong></span> will generate a declaration of a temporary
variable in which to store the value of the C output parameter and a
statement that sets the C++ output parameter from the temporary variable.
In this case it may be necessary to have an
<code class="function">_INITIALIZATION()</code> describing how to set a
<code class="classname">Gdk::Rectangle&</code> from a
<code class="classname">GdkRectangle*</code> such as the following:
</p>
<pre class="programlisting">
_INITIALIZATION(`Gdk::Rectangle&',`GdkRectangle', `$3 =
Glib::wrap(&($4))')
</pre>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="gmmproc-string-parameter-processing"></a>String Parameter Processing</h4></div></div></div>
<p>
A string-valued input parameter in a C++ method is usually a
<span class="type">const Glib::ustring&</span> or a <span class="type">const std::string&</span>.
In C code it's a <span class="type">const gchar*</span>. When an empty string is converted
to <span class="type">const gchar*</span>, it can be converted either to <code class="literal">nullptr</code>
or to a pointer to an empty string (with <code class="methodname">c_str()</code>).
Some parameters in some C functions accept a <code class="literal">nullptr</code>, and
interpret it in a special way. Other parameters must not be <code class="literal">nullptr</code>.
</p>
<p>
The default conversion in <code class="function">_WRAP_METHOD()</code> and similar
directives is
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>for mandatory parameters (with or without default values):
empty string to empty string,</p></li>
<li class="listitem"><p>for optional parameters (with appended <code class="literal">{?}</code>):
empty string to <code class="literal">nullptr</code>.</p></li>
</ul></div>
<p>
If the default conversion is not the best conversion, append <code class="literal">{NULL}</code>
to a mandatory parameter or <code class="literal">{?!NULL}</code> to an optional
parameter (<code class="literal">!NULL</code> = not <code class="literal">NULL</code>). If you
append both a C parameter name and <code class="literal">NULL</code>, separate them
with a space: <code class="literal">{c_param_name NULL}</code>.
</p>
</div>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="gmmproc-basic-types"></a>Basic Types</h3></div></div></div>
<p>Some of the basic types that are used in C APIs have better alternatives
in C++. For example, there's no need for a <span class="type">gboolean</span> type since
C++ has <span class="type">bool</span>. The following list shows some commonly-used
types in C APIs and what you might convert them to in a C++ wrapper library.
</p>
<div class="segmentedlist">
<div class="title"><strong><span class="title">Basic Type equivalents</span></strong></div>
<table border="0">
<thead><tr class="segtitle">
<th>C type</th>
<th>C++ type</th>
</tr></thead>
<tbody>
<tr class="seglistitem">
<td class="seg"><span class="type">gboolean</span></td>
<td class="seg"><span class="type">bool</span></td>
</tr>
<tr class="seglistitem">
<td class="seg"><span class="type">gint</span></td>
<td class="seg"><span class="type">int</span></td>
</tr>
<tr class="seglistitem">
<td class="seg"><span class="type">guint</span></td>
<td class="seg"><span class="type">guint</span></td>
</tr>
<tr class="seglistitem">
<td class="seg"><span class="type">gdouble</span></td>
<td class="seg"><span class="type">double</span></td>
</tr>
<tr class="seglistitem">
<td class="seg"><span class="type">gunichar</span></td>
<td class="seg"><span class="type">gunichar</span></td>
</tr>
<tr class="seglistitem">
<td class="seg"><span class="type">gchar*</span></td>
<td class="seg">
<code class="classname">Glib::ustring</code> (or <code class="classname">std::string</code> for filenames)</td>
</tr>
</tbody>
</table>
</div>
</div>
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