Variadic functions

Some C library functions are variadic. Unfortunately cgo does not support calling variadic C functions.

format functions

Some C library variadic functions accept trailing arguments that include a printf style format string followed by arguments to insert in to the format string. gtk_message_dialog_new is an example of such a function.

The equivalent functions in gobbi accept fmt package compatible arguments. This is because fmt.Sprint is used to format a string before passing it as the last argument to the wrapped C function.

A much simplified representation of such a gobbi function might help to make this clearer.

package gtk

// a gobbi function
func SomeFormatFunction(
	a string, b int,
	format string, args ...interface{},
) {
	c_a := C.String(a)
	c_b := C.int(b)

	formattedString := fmt.Sprintf(format, args...)
	c_formattedString := C.String(formattedString)

	C.some_format_function(c_a, c_b, c_formattedString)
}

// ----------------------------- //

// some application code
func aFunction () {
    gtk.SomeFormatFunction(
        "a string", 123,
        "the %s is %d", "answer", 42,
    )
}

unsupported variadic functions

Many variadic functions are not supported by gobbi because it would be impractical to automatically generate code that would support them.

array functions

In some cases there is an alternative function that accepts an array as the final argument instead. For example gtk_list_store_new is not supported, but gtk_list_store_newv is supported as gtk.ListStoreNewv.

multiple functions

There are other variadac functions that may not have an array equivalent version, but their functionality can be achieved through a combination of functions.

An example of this is the unsupported gtk_text_buffer_create_tag function. A work around might be code like this.

    tag := gtk.TextTagNew("my_tag_name")
    tagTable := gtk.TextTagTableNew()
    tagTable.Add(tag)
    buffer := gtk.TextBufferNew(tagTable)

    editable := gobject.ValueNew(gobject.TYPE_BOOLEAN)
    editable.SetBoolean(false)
    tag.Object().SetProperty("property-name", editable)

    indent := gobject.ValueNew(gobject.TYPE_INT)
    indent.SetInt(4)
    tag.Object().SetProperty("indent", indent)