The .hg and .ccg files

The .hg and .ccg source files are very much like .h and .cc C++ source files, but they contain extra macros, such as _CLASS_GOBJECT() and _WRAP_METHOD(), from which gmmproc 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.

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, gtkmm's button.hg looks roughly like this:

#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

The macros in this example do the following:

_DEFS()

Specifies the destination directory for generated sources, and the name of the main .defs file that gmmproc should parse.

_PINCLUDE()

Tells gmmproc to include a header in the generated private/button_p.h file.

_CLASS_GTKOBJECT()

Tells gmmproc to add some typedefs, constructors, and standard methods to this class, as appropriate when wrapping a widget.

_IMPLEMENTS_INTERFACE()

Tells gmmproc to add initialization code for the interface.

_CTOR_DEFAULT

Add a default constructor.

_WRAP_METHOD(), _WRAP_SIGNAL(), _WRAP_PROPERTY(), and _WRAP_CHILD_PROPERTY()

Add methods to wrap parts of the C API.

The .h and .cc files will be generated from the .hg and .ccg files by processing them with gmmproc like so, though this happens automatically when using the above build structure:

$ cd gtk/src
$ /usr/lib/glibmm-2.4/proc/gmmproc -I ../../tools/m4 --defs . button . ./../gtkmm

Notice that we provided gmmproc 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.

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.

The macros are explained in more detail in the following sections.

G.3.1. m4 Conversions

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 tools/m4/ 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:

_CONVERSION(`GtkTreeView*',`TreeView*',`Glib::wrap($3)')

$3 will be replaced by the parameter name when this conversion is used by gmmproc.

Some extra macros make this easier and consistent. Look in gtkmm's .m4 files for examples. For instance:

_CONVERSION(`PrintSettings&',`GtkPrintSettings*',__FR2P)
_CONVERSION(`const PrintSettings&',`GtkPrintSettings*',__FCR2P)
_CONVERSION(`const Glib::RefPtr<Printer>&',`GtkPrinter*',__CONVERT_REFPTR_TO_P($3))

G.3.2. m4 Initializations

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 void 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.

For example, if there was a C function that returned a GtkWidget* 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:

_INITIALIZATION(`Gtk::Widget&',`GtkWidget*',`$3 = Glib::wrap($4)')

$3 will be replaced by the output parameter name of the C++ method and $4 will be replaced by the return of the C function when this initialization is used by gmmproc. For convenience, $1 will also be replaced by the C++ type without the ampersand (&) and $2 will be replaced by the C type.

G.3.3. Class macros

The class macro declares the class itself and its relationship with the underlying C type. It generates some internal constructors, the member gobject_, typedefs, the gobj() accessors, type registration, and the Glib::wrap() method, among other things.

Other macros, such as _WRAP_METHOD() and _WRAP_SIGNAL() may only be used after a call to a _CLASS_* macro.

G.3.3.1. _CLASS_GOBJECT

This macro declares a wrapper for a type that is derived from GObject, but whose wrapper is not derived from Gtk::Object.

_CLASS_GOBJECT( C++ class, C class, C casting macro, C++ base class, C base class )

For instance, from accelgroup.hg:

_CLASS_GOBJECT(AccelGroup, GtkAccelGroup, GTK_ACCEL_GROUP, Glib::Object, GObject)

G.3.3.2. _CLASS_GTKOBJECT

This macro declares a wrapper for a type whose wrapper is derived from Gtk::Object, such as a widget or dialog.

_CLASS_GTKOBJECT( C++ class, C class, C casting macro, C++ base class, C base class )

For instance, from button.hg:

_CLASS_GTKOBJECT(Button, GtkButton, GTK_BUTTON, Gtk::Bin, GtkBin)

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.

You might also derive non-widget classes from Gtk::Object so they can be used without Glib::RefPtr. For instance, they could then be instantiated with Gtk::manage() 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.

G.3.3.3. _CLASS_BOXEDTYPE

This macro declares a wrapper for a non-GObject struct, registered with g_boxed_type_register_static().

_CLASS_BOXEDTYPE( C++ class, C class, new function, copy function, free function )

For instance, from Gdk::RGBA:

_CLASS_BOXEDTYPE(RGBA, GdkRGBA, NONE, gdk_rgba_copy, gdk_rgba_free)

G.3.3.4. _CLASS_BOXEDTYPE_STATIC

This macro declares a wrapper for a simple assignable struct such as GdkRectangle. It is similar to _CLASS_BOXEDTYPE, but the C struct is not allocated dynamically.

_CLASS_BOXEDTYPE_STATIC( C++ class, C class )

For instance, for Gdk::Rectangle:

_CLASS_BOXEDTYPE_STATIC(Rectangle, GdkRectangle)

G.3.3.5. _CLASS_OPAQUE_COPYABLE

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.

_CLASS_OPAQUE_COPYABLE( C++ class, C class, new function, copy function, free function )

For instance, from Glib::Checksum:

_CLASS_OPAQUE_COPYABLE(Checksum, GChecksum, NONE, g_checksum_copy, g_checksum_free)

G.3.3.6. _CLASS_OPAQUE_REFCOUNTED

This macro declares a wrapper for a reference-counted opaque struct. The C++ wrapper cannot be directly instantiated and can only be used with Glib::RefPtr.

_CLASS_OPAQUE_REFCOUNTED( C++ class, C class, new function, ref function, unref function )

For instance, for Pango::Coverage:

_CLASS_OPAQUE_REFCOUNTED(Coverage, PangoCoverage, pango_coverage_new, pango_coverage_ref, pango_coverage_unref)

G.3.3.7. _CLASS_GENERIC

This macro can be used to wrap structs which don't fit into any specialized category.

_CLASS_GENERIC( C++ class, C class )

For instance, for Pango::AttrIter:

_CLASS_GENERIC(AttrIter, PangoAttrIterator)

G.3.3.8. _CLASS_INTERFACE

This macro declares a wrapper for a type that is derived from GTypeInterface.

_CLASS_INTERFACE( C++ class, C class, C casting macro, C interface struct, Base C++ class (optional), Base C class (optional) )

For instance, from celleditable.hg:

_CLASS_INTERFACE(CellEditable, GtkCellEditable, GTK_CELL_EDITABLE, GtkCellEditableIface)

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 loadableicon.hg:

_CLASS_INTERFACE(LoadableIcon, GLoadableIcon, G_LOADABLE_ICON, GLoadableIconIface, Icon, GIcon)

G.3.4. Constructor macros

The _CTOR_DEFAULT() and _WRAP_CTOR() macros add constructors, wrapping the specified *_new() 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 g_object_new() call. These constructors never actually call the *_new() C functions, because gtkmm must actually instantiate derived GTypes, and the *_new() C functions are meant only as convenience functions for C programmers.

When using _CLASS_GOBJECT(), the constructors should be protected (rather than public) and each constructor should have a corresponding _WRAP_CREATE() in the public section. This prevents the class from being instantiated without using a RefPtr. For instance:

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)

G.3.4.1. _CTOR_DEFAULT

This macro creates a default constructor with no arguments.

G.3.4.2. _WRAP_CTOR

This macro creates a constructor with arguments, equivalent to a *_new() C function. It won't actually call the *_new() function, but will simply create an equivalent constructor with the same argument types. It takes a C++ constructor signature, and a C function name.

It also takes an optional extra argument:

errthrow

This tells gmmproc that the C *_new() has a final GError** parameter which should be ignored.

G.3.4.3. Hand-coding constructors

When a constructor must be partly hand written because, for instance, the *_new() C function's parameters do not correspond directly to object properties, or because the *_new() C function does more than call g_object_new(), the _CONSTRUCT() macro may be used in the .ccg file to save some work. The _CONSTRUCT macro takes a series of property names and values. For instance, from button.ccg:

Button::Button(const Glib::ustring& label, bool mnemonic)
:
  _CONSTRUCT("label", label.c_str(), "use_underline", gboolean(mnemonic))
{}

G.3.5. Macros that suppress generation of some code

Some macros suppress the generation of some code when they are used after a _CLASS_* 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.

G.3.5.1. _CUSTOM_DEFAULT_CTOR

Suppresses declaration and definition of default constructor in _CLASS_BOXEDTYPE, _CLASS_BOXEDTYPE_STATIC and _CLASS_OPAQUE_COPYABLE.

G.3.5.2. _CUSTOM_CTOR_CAST

Suppresses declaration and definition of the constructor that takes a pointer to the wrapped C object in _CLASS_BOXEDTYPE and _CLASS_BOXEDTYPE_STATIC.

Suppresses definition of the constructor that takes a pointer to the wrapped C object in _CLASS_GOBJECT, _CLASS_GTKOBJECT, _CLASS_INTERFACE and _CLASS_OPAQUE_COPYABLE.

G.3.5.3. _CUSTOM_DTOR

Suppresses definition of destructor in _CLASS_GOBJECT and _CLASS_GTKOBJECT.

G.3.5.4. _CUSTOM_MOVE_OPERATIONS

Suppresses declaration and definition of move constructor and move assignment operator in _CLASS_GOBJECT.

For example:

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;
  // ...
};

G.3.5.5. _CUSTOM_WRAP_NEW

Suppresses definition of Glib::wrap_new() function in _CLASS_GOBJECT.

G.3.5.6. _CUSTOM_WRAP_FUNCTION

Suppresses definition of Glib::wrap() function in _CLASS_GOBJECT and _CLASS_GTKOBJECT.

G.3.5.7. _NO_WRAP_FUNCTION

Suppresses declaration and definition of Glib::wrap() function in _CLASS_GOBJECT, _CLASS_BOXEDTYPE, _CLASS_BOXEDTYPE_STATIC, _CLASS_OPAQUE_COPYABLE, _CLASS_INTERFACE and _CLASS_GTKOBJECT.

G.3.6. Method macros

G.3.6.1. _WRAP_METHOD

This macro generates the C++ method to wrap a C function.

_WRAP_METHOD( C++ method signature, C function name)

For instance, from entry.hg:

_WRAP_METHOD(void set_text(const Glib::ustring& text), gtk_entry_set_text)

The C function (e.g. gtk_entry_set_text) is described more fully in the .defs file, and the convert*.m4 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 *_docs.xml and *_docs_override.xml files.

There are some optional extra arguments:

refreturn

Do an extra reference() on the return value, in case the C function does not provide a reference.

errthrow

Use the last GError** parameter of the C function to throw an exception.

deprecated ["<text>"]

Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

constversion

Just call the non-const version of the same function, instead of generating almost duplicate code.

newin "<version>"

Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

ifdef <identifier>

Puts the generated code in #ifdef blocks.

slot_name <parameter_name>

Specifies the name of the slot parameter of the method, if it has one. This enables gmmproc to generate code to copy the slot and pass the copy on to the C function in its final gpointer user_data parameter. The slot_callback option must also be used to specify the name of the glue callback function to also pass on to the C function.

slot_callback <function_name>

Used in conjunction with the slot_name 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.

no_slot_copy

Tells gmmproc 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 slot_name and slot_callbback options respectively.

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:

  • Objects used via RefPtr: Pass the RefPtr as a const reference. For instance, const Glib::RefPtr<Gtk::FileFilter>& filter.
  • Const Objects used via RefPtr: If the object should not be changed by the function, then make sure that the object is const, even if the RefPtr is already const. For instance, const Glib::RefPtr<const Gtk::FileFilter>& filter.
  • Wrapping GList* and GSList* 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 std::vector type. For instance, std::vector< Glib::RefPtr<Gdk::Pixbuf> >. You may need to define a Traits type to specify how the C and C++ types should be converted.
  • Wrapping GList* and GSList* 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:
    #m4 _CONVERSION(`GSList*',`std::vector<Widget*>',`Glib::SListHandler<Widget*>::slist_to_vector($3, Glib::OWNERSHIP_SHALLOW)')

G.3.6.2. _WRAP_METHOD_DOCS_ONLY

This macro is like _WRAP_METHOD(), 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.

_WRAP_METHOD_DOCS_ONLY(C function name)

For instance, from container.hg:

_WRAP_METHOD_DOCS_ONLY(gtk_container_remove)

There are some optional extra arguments:

errthrow

Excludes documentation of the last GError** parameter of the C function.

newin "<version>"

Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

G.3.6.3. _IGNORE, _IGNORE_SIGNAL, _IGNORE_PROPERTY, _IGNORE_CHILD_PROPERTY

gmmproc 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 gmmproc stop complaining.

_IGNORE(C function name 1, C function name 2, etc) _IGNORE_SIGNAL(C signal name 1, C signal name 2, etc) _IGNORE_PROPERTY(C property name 1, C property name 2, etc) _IGNORE_CHILD_PROPERTY(C child property name 1, C child property name 2, etc)

For instance, from flowbox.hg:

_IGNORE(gtk_flow_box_set_filter_func, gtk_flow_box_set_sort_func)
_IGNORE_SIGNAL(activate-cursor-child, toggle-cursor-child, move-cursor)

G.3.6.4. _WRAP_SIGNAL

This macro generates the C++ libsigc++-style signal to wrap a C GObject signal. It actually generates a public accessor method, such as signal_clicked(), which returns a proxy object. gmmproc uses the .defs file to discover the C parameter types and the .m4 convert files to discover appropriate type conversions.

_WRAP_SIGNAL( C++ signal handler signature, C signal name)

For instance, from button.hg:

_WRAP_SIGNAL(void clicked(),"clicked")

Signals usually have function pointers in the GTK struct, with a corresponding enum value and a g_signal_new() in the .c file.

There are some optional extra arguments:

no_default_handler

Do not generate an on_something() 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.

custom_default_handler

Generate a declaration of the on_something() virtual method in the .h file, but do not generate a definition in the .cc file. Use this when you must generate the definition by hand.

custom_c_callback

Do not generate a C callback function for the signal. Use this when you must generate the callback function by hand.

refreturn

Do an extra reference() on the return value of the on_something() virtual method, in case the C function does not provide a reference.

deprecated ["<text>"]

Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

newin "<version>"

Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

ifdef <identifier>

Puts the generated code in #ifdef blocks.

exception_handler <method_name>

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.

detail_name <parameter_name>

Adds a const Glib::ustring& parameter to the signal_something() method. Use it, if the signal accepts a detailed signal name, i.e. if the underlying C code registers the signal with the G_SIGNAL_DETAILED flag.

two_signal_methods

Used in conjunction with the detail_name option to generate two signal_something() methods, one without a parameter and one with a parameter without a default value. With only the detail_name option one method is generated, with a parameter with default value. Use the two_signal_methods option, if it's necessary in order to preserve ABI.

G.3.6.5. _WRAP_PROPERTY

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. gmmproc uses the .defs file to discover the C type and the .m4 convert files to discover appropriate type conversions.

_WRAP_PROPERTY(C property name, C++ type)

For instance, from button.hg:

_WRAP_PROPERTY("label", Glib::ustring)

There are some optional extra arguments:

deprecated ["<text>"]

Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

newin "<version>"

Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

G.3.6.6. _WRAP_VFUNC

This macro generates the C++ method to wrap a virtual C function.

_WRAP_VFUNC( C++ method signature, C function name)

For instance, from widget.hg:

_WRAP_VFUNC(SizeRequestMode get_request_mode() const, get_request_mode)

The C function (e.g. get_request_mode) is described more fully in the *_vfuncs.defs file, and the convert*.m4 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.

There are some optional extra arguments:

refreturn

Do an extra reference() on the return value of the something_vfunc() function, in case the virtual C function does not provide a reference.

refreturn_ctype

Do an extra reference() on the return value of an overridden something_vfunc() function in the C callback function, in case the calling C function expects it to provide a reference.

keep_return

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.

errthrow

Use the last GError** parameter of the C virtual function (if there is one) to throw an exception.

custom_vfunc

Do not generate a definition of the vfunc in the .cc file. Use this when you must generate the vfunc by hand.

custom_vfunc_callback

Do not generate a C callback function for the vfunc. Use this when you must generate the callback function by hand.

ifdef <identifier>

Puts the generated code in #ifdef blocks.

slot_name <parameter_name>

Specifies the name of the slot parameter of the method, if it has one. This enables gmmproc to generate code to copy the slot and pass the copy on to the C function in its final gpointer user_data parameter. The slot_callback option must also be used to specify the name of the glue callback function to also pass on to the C function.

slot_callback <function_name>

Used in conjunction with the slot_name 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.

no_slot_copy

Tells gmmproc 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 slot_name and slot_callbback options respectively.

return_value <value>

Defines a non-default return value.

err_return_value <value>

Defines a non-default return value, used only if the C++ something_vfunc() 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.

exception_handler <method_name>

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.

A rule to which there may be exceptions: If the virtual C function returns a pointer to an object derived from GObject, i.e. a reference-counted object, then the virtual C++ function shall return a Glib::RefPtr<> object. One of the extra arguments refreturn or refreturn_ctype is required.

G.3.6.7. _WRAP_CHILD_PROPERTY

This macro generates the C++ method to wrap a GtkContainer child property. (See GtkContainer for more information about child properties). Similarly to _WRAP_PROPERTY, you must specify the property name and the wanted C++ type for the property. gmmproc uses the .defs file to discover the C type and the .m4 convert files to discover appropriate type conversions.

_WRAP_CHILD_PROPERTY(C child property name, C++ type)

For instance, from notebook.hg:

_WRAP_CHILD_PROPERTY("tab-expand", bool)

_WRAP_CHILD_PROPERTY() accepts the same optional arguments as _WRAP_PROPERTY().

G.3.7. Other macros

G.3.7.1. _IMPLEMENTS_INTERFACE

This macro generates initialization code for the interface.

_IMPLEMENTS_INTERFACE(C++ interface name)

For instance, from grid.hg:

_IMPLEMENTS_INTERFACE(Orientable)

There is one optional extra argument:

ifdef <identifier>

Puts the generated code in #ifdef blocks.

G.3.7.2. _WRAP_ENUM

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.

For instance, from enums.hg:

_WRAP_ENUM(WindowType, GtkWindowType)

There are some optional extra arguments:

NO_GTYPE

Use this option, if the enum is not a GType. This is the case when there is no *_get_type() 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.

For example, from icontheme.hg:

_WRAP_ENUM(IconLookupFlags, GtkIconLookupFlags, NO_GTYPE)
      

s#<from>#<to>#

Substitutes (part of) the name of one or more enum constants. You can add any number of substitutions.

For example, from iochannel.hg in glibmm:

_WRAP_ENUM(SeekType, GSeekType, NO_GTYPE, s#^SEEK_#SEEK_TYPE_#)
      

deprecated ["<text>"]

Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

newin "<version>"

Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

G.3.7.3. _WRAP_ENUM_DOCS_ONLY

This macro just generates a Doxygen documentationn block for the enum. This is useful for enums that can't be wrapped with _WRAP_ENUM() 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 _WRAP_ENUM() and also process the same options (though NO_GTYPE is just ignored because it makes no difference when just generating the enum's documentation).

G.3.7.4. _WRAP_GERROR

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.

This exception can then be thrown by methods which are generated from _WRAP_METHOD() with the errthrow option.

For instance, from pixbuf.hg:

_WRAP_GERROR(PixbufError, GdkPixbufError, GDK_PIXBUF_ERROR)

_WRAP_GERROR() accepts the same optional arguments as _WRAP_ENUM().

G.3.7.5. _MEMBER_GET / _MEMBER_SET

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.

_MEMBER_GET(C++ name, C name, C++ type, C type)

_MEMBER_SET(C++ name, C name, C++ type, C type)

For example, in rectangle.hg:

_MEMBER_GET(x, x, int, int)

G.3.7.6. _MEMBER_GET_PTR / _MEMBER_SET_PTR

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.

_MEMBER_GET_PTR(C++ name, C name, C++ type, C type)

_MEMBER_SET_PTR(C++ name, C name, C++ type, C type)

For example, for Pango::Analysis in item.hg:

// _MEMBER_GET_PTR(engine_lang, lang_engine, EngineLang*, PangoEngineLang*)
// It's just a comment. It's difficult to find a real-world example.

G.3.7.7. _MEMBER_GET_GOBJECT / _MEMBER_SET_GOBJECT

Use these macros to provide getters and setters for a data member that is a GObject type that must be referenced before being returned.

_MEMBER_GET_GOBJECT(C++ name, C name, C++ type, C type)

_MEMBER_SET_GOBJECT(C++ name, C name, C++ type, C type)

For example, in Pangomm, layoutline.hg:

_MEMBER_GET_GOBJECT(layout, layout, Pango::Layout, PangoLayout*)

G.3.8. gmmproc Parameter Processing

gmmproc allows processing the parameters in a method signature for the macros that process method signatures (like _WRAP_METHOD(), _WRAP_CTOR() and _WRAP_CREATE()) in a variety of ways:

G.3.8.1. Parameter Reordering

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 Gtk::Widget class:

        void gtk_widget_set_device_events(GtkWidget* widget, GdkDevice* device,
        GdkEventMask events);
      
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:
        _WRAP_METHOD(void set_device_events(Gdk::EventMask events{events},
        const Glib::RefPtr<const Gdk::Device>& device{device}),
        gtk_widget_set_device_events)
      
The {c_param_name} following the method parameter names tells gmmproc to map the C++ parameter to the specified C parameter within the {}. Since the C++ parameter names correspond to the C ones, the above could be re-written as:
        _WRAP_METHOD(void set_device_events(Gdk::EventMask events{.}, const
        Glib::RefPtr<const Gdk::Device>& device{.}),
        gtk_widget_set_device_events)
      

Please note that when reordering parameters for a _WRAP_SIGNAL() method signature, the C parameter names would always be p0, p1, etc. because the generate_extra_defs utility uses those parameter names no matter what the C API's parameter names may be. It's how the utility is written presently.

G.3.8.2. Optional Parameter Processing

For all macros processing method signatures except _WRAP_SIGNAL() and _WRAP_VFUNC() 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 *_new() function were being wrapped as a constructor in the Gtk::ToolButton class:

        GtkToolItem* gtk_tool_button_new(GtkWidget* icon_widget, const gchar*
        label);
      
Also, say that the C API allowed NULL for the function's label parameter so that that parameter is optional. It would be possible to have gmmproc generate the original constructor (with all the parameters) along with an additional constructor without that optional parameter by appending a {?} to the parameter name like so:
        _WRAP_CTOR(ToolButton(Widget& icon_widget, const Glib::ustring&
        label{?}), gtk_tool_button_new)
      
In this case, two constructors would be generated: One with the optional parameter and one without it.

G.3.8.3. Output Parameter Processing

With _WRAP_METHOD() 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 {OUT} to the output parameter name. For example, if gtk_widget_get_request_mode() is declared as the following:

        GtkSizeRequestMode gtk_widget_get_request_mode(GtkWidget* widget);
      
And having the C++ method set an output parameter is desired instead of returning a SizeRequestMode, something like the following could be used:
        _WRAP_METHOD(void get_request_mode(SizeRequestMode& mode{OUT})
        const, gtk_widget_get_request_mode)
      
The {OUT} appended to the name of the mode output parameter tells gmmproc 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:
        _INITIALIZATION(`SizeRequestMode&',`GtkSizeRequestMode',`$3 =
        (SizeRequestMode)($4)')
      
Which could also be written as:
        _INITIALIZATION(`SizeRequestMode&',`GtkSizeRequestMode',`$3 =
        ($1)($4)')
      

_WRAP_METHOD() 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 rect:

        gboolean gtk_icon_view_get_cell_rect(GtkIconView* icon_view,
        GtkTreePath* path, GtkCellRenderer* cell, GdkRectangle* rect);
      
To have gmmproc place the value returned in the C++ rect output parameter, something like the following _WRAP_METHOD() directive could be used:
        _WRAP_METHOD(bool get_cell_rect(const TreeModel::Path& path, const
        CellRenderer& cell, Gdk::Rectangle& rect{>>}) const,
        gtk_icon_view_get_cell_rect)
      
The {>>} following the rect parameter name indicates that the C++ output parameter should be set from the value returned in the C parameter from the C function. gmmproc 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 _INITIALIZATION() describing how to set a Gdk::Rectangle& from a GdkRectangle* such as the following:
        _INITIALIZATION(`Gdk::Rectangle&',`GdkRectangle', `$3 =
        Glib::wrap(&($4))')
      

G.3.8.4. String Parameter Processing

A string-valued input parameter in a C++ method is usually a const Glib::ustring& or a const std::string&. In C code it's a const gchar*. When an empty string is converted to const gchar*, it can be converted either to nullptr or to a pointer to an empty string (with c_str()). Some parameters in some C functions accept a nullptr, and interpret it in a special way. Other parameters must not be nullptr.

The default conversion in _WRAP_METHOD() and similar directives is

  • for mandatory parameters (with or without default values): empty string to empty string,
  • for optional parameters (with appended {?}): empty string to nullptr.
If the default conversion is not the best conversion, append {NULL} to a mandatory parameter or {?!NULL} to an optional parameter (!NULL = not NULL). If you append both a C parameter name and NULL, separate them with a space: {c_param_name NULL}.

G.3.9. Basic Types

Some of the basic types that are used in C APIs have better alternatives in C++. For example, there's no need for a gboolean type since C++ has bool. The following list shows some commonly-used types in C APIs and what you might convert them to in a C++ wrapper library.

Basic Type equivalents

C type: gboolean

C++ type: bool

C type: gint

C++ type: int

C type: guint

C++ type: guint

C type: gdouble

C++ type: double

C type: gunichar

C++ type: gunichar

C type: gchar*

C++ type: Glib::ustring (or std::string for filenames)