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<TITLE>Constructor, Destructor, and Purge Member Function</TITLE>
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<b>Data Structures and Algorithms 
with Object-Oriented Design Patterns in C++</b><br>
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<H3><A NAME="SECTION0010633000000000000000">Constructor, Destructor, and <tt>Purge</tt> Member Function</A></H3>
<P>
Program&nbsp;<A HREF="page279.html#proggentree1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page279.html#proggentree1c"><IMG  ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A> defines the <tt>GeneralTree</tt>
constructor, destructor, and the <tt>Purge</tt> member function.
According to Definition&nbsp;<A HREF="page251.html#defntree" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page251.html#defntree"><IMG  ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A>,
a general tree must contain at least one node--an empty tree is not allowed.
Therefore, the constructor takes one argument,
a reference to an <tt>Object</tt> instance.
The constructor initializes the member variables as follows:
The variable <tt>key</tt> is made to point at the object argument;
the <tt>degree</tt> is set to zero; and,
the linked list <tt>list</tt> is configured as an empty list.
The running time of the constructor is clearly <I>O</I>(1).
<P>
<P><A NAME="16764">&#160;</A><A NAME="proggentree1c">&#160;</A> <IMG WIDTH=575 HEIGHT=393 ALIGN=BOTTOM ALT="program16667" SRC="img1171.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1171.gif"  ><BR>
<STRONG>Program:</STRONG> <tt>GeneralTree</tt> Class Constructor, Destructor 	and <tt>Purge</tt> Member Function Definitions<BR>
<P>
<P>
The <tt>Purge</tt> member function is inherited from the <tt>Container</tt>
class interface.
The purpose of <tt>Purge</tt> is to delete all contained objects
and to release the associated storage
if the container is the owner of those objects.
Each node in a <tt>GeneralTree</tt> is a container
with two varieties of contained objects--the root object and the subtrees.
The approach taken in this implementation stipulates that
the ownership of the root object is determined in the usual way
but that all the subtrees of a given tree always are owned by that tree.
<P>
The <tt>GeneralTree</tt> class destructor simply calls the <tt>Purge</tt>
member function to do its work.
The <tt>Purge</tt> function first deletes the root object
if it is the owner of that object.
Then, it traverses the linked lists,
deleting each of the attached subtrees.
Finally, it deletes the linked list itself.
Given a tree comprised of <I>n</I> nodes,
the running time of the <tt>Purge</tt> function is
 <IMG WIDTH=176 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline63934" SRC="img1172.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1172.gif"  > in the worst case.
The factor (2<I>n</I>-1) is the sum of the number of contained objects deleted, <I>n</I>,
and the number of trees deleted, <I>n</I>-1.
<P>
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