Signal Marshallers

What are Signal Marshallers?

Marshals are functions which all have the same prototype: they take a GtkObject, a GtkSignalFunc, a gpointer, and an array of argument values. The functions are names gtk_marshall_RETURNTYPE__PARAMTYPE1_PARAMTYPE2....

They then call a native function: the GtkObject is the first parameter passed in. The arguments are passed in the native calling convention: chars, shorts, ints, longs may be packed on the stack, or tucked in registers: it doesn't matter because the same calling convention will be generated inside the gtkmarshal code as is expected where you define your handlers.

So the function named:

gtk_marshal_BOOL__POINTER_INT_INT_UINT(GtkObject*, GtkSignalFunc, gpointer, GtkArg*);

will call the GtkSignalFunc assuming it was a function with signature:

gboolean sigfunc(gpointer,gint,gint,guint);

Writing Custom Marshals

Marshals are primarily used as arguments to gtk_signal_new(). Sometimes, you may find that a marshaller you need isn't available in the standard list. Then you have to write your own.

If you wish to define a signal with a new type of argument list. Suppose you want 2 pointers and 2 integers. You would write:

typedef int (*GtkSignal_INT__POINTER_POINTER_INT_INT)( gpointer, gpointer, gint, gint ); void marshal_INT__POINTER_POINTER_INT_INT(GtkObject* object, GtkSignalFunc func, gpointer func_data, GtkArg* args) { GtkSignal_NONE__POINTER_POINTER_INT_INT rfunc; gint* return_val; return_val = GTK_RETLOC_INT(args[4]); rfunc = (GtkSignal_INT__POINTER_POINTER_INT_INT)func; *return_val = (*rfunc)(object, GTK_VALUE_POINTER(args[0]), GTK_VALUE_POINTER(args[1]), GTK_VALUE_INT(args[2]), GTK_VALUE_INT(args[3]), func_data); }

gtk_signal_default_marshaller

#define gtk_signal_default_marshaller gtk_marshal_NONE__NONE

A marshaller that returns void and takes no extra parameters.