GStreamer polices for various forms of library output, including error cases.


g_return_...
============
The parameters of a function are checked for validity (non-NULL, correct type, etc.) with g_return[_val]_if_fail, i.e.:

gst_element_connect (GstElement *src, gchar *srcpadname,
                     GstElement *dest, gchar *destpadname) {
  g_return_if_fail (src != NULL);
  g_return_if_fail (GST_IS_ELEMENT(src));
  g_return_if_fail (srcpadname != NULL);
  g_return_if_fail (dest != NULL);
  g_return_if_fail (GST_IS_ELEMENT(dest));
  g_return_if_fail (destpadname != NULL);

This will inform the user of the library of any basic problems with the arguments they pass, such as a NULL pointer.


ERROR
=====
The ERROR macro will be used whenever there is some other type of flaw in the data passed, at a GStreamer-specific 
level:

  srcpad = gst_element_get_pad (src, srcpadname);
  if (srcpad == NULL) {
    ERROR(src,"source element has no pad \"%s\"",srcpadname);
    return;
  }

An ERROR will generally cause ceasation of the application, and ideally launch gdb.


INFO
====
The INFO macro will be used to output any interesting state from the library, such as plugin loading and various events 
of interest.  They will be separated into categories that can be individually enabled and disabled.

Categories (first draft of list, unordered):

cothreads			[cothreads.c]
gst initialization		[gst.c]
autoplug results		[autoplug.c]
autoplug attempts		[autoplug.c]
bin parentage issues		[gstbin.c]
plan generation			[gstbin.c]
schedule generation		[gstschedule.c]
schedule implementation		[gstpad.c, gstbin.c, etc.]
buffer operations		[gstbuffer.h]
caps matching			[gstcaps.c]
clock stuff			[gstclock.c]
element pad operations		[gstelement.c]
elementfactory operations	[gstelementfactory.c]
pad creation/connection		[gstpad.c]
pipeline stuff			[gstpipeline.c]
plugin loading			[gstplugin.c]
plugin loading errors		[gstplugin.c]
properties operations		[gstprops.c]
thread creation/management	[gstthread.c]
type operations			[gsttype.c]
XML load/save			[gstxml.c]