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+><A
+NAME="AEN50"
+>2.3. Using the reading context</A
+></H1
+><P
+> If you have read the tutorials about writing a text and a graphic module, you
+should be fairly ready to use the information provided to your hook by the
+reading API.
+</P
+><P
+> The data structures of the reading context are based on the gobject, a
+object-oriented library from the glib. Some evolved types that are found in the
+context also comes from the "glib" (GArray, GHashTable and so on). For detailed
+information about "gobjects" and the "glib", see the <A
+HREF="http://www.gtk.org"
+TARGET="_top"
+>www.gtk.org</A
+> website. They provide a complete
+API reference about the data types they provide.
+</P
+><P
+> The reading context is object oriented. It is described by the lttv/tracecontext.h
+header. Is can be illustrated with this UML class diagram :
+</P
+><P
+> <DIV
+CLASS="mediaobject"
+><P
+><IMG
+SRC="lttv-context.png"
+ALIGN="center"><DIV
+CLASS="caption"
+><P
+>Linux Trace Toolkit Viewer Reading Context Class Diagram</P
+></DIV
+></P
+></DIV
+>
+</P
+><P
+> Though, for performance's sake, navigating through it is not as encapsulated as
+it could. Consider the class attributes to be all public (no get/set functions).
+Sometimes, iteration upon a specific element can be uneasy. For example, you may
+have to get the number of tracefiles in a trace from the "vt" field of the trace
+context to be able to iterate over all the tracefiles contained by the trace.
+</P
+><P
+> To facilitate the common operations on the reading context, LTTV now provides a
+header that consists of simple macros : lttv/contextmacros.h. It gives an object
+look-and-feel to the context classes. Simple "GET" macros can be used to easily
+access the different fields are iterate over the elements (and get the total
+number of elements too).
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