%TRUE if all children are to be given equal space allotments.
the number of pixels to place by default between children.
a new #GtkHBox.
Deprecated: You can use gtk_box_new() with %GTK_ORIENTATION_HORIZONTAL instead, which is a quick and easy change. But the recommendation is to switch to #GtkGrid, since #GtkBox is going to go away eventually. See [Migrating from other containers to GtkGrid][gtk-migrating-GtkGrid].
ConstructionException GTK+ fails to create the object.
Creates a new #GtkHBox.