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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
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>2.3. Using the reading context</A
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><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
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> 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
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> <DIV
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><P
><IMG
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><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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