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<b>Data Structures and Algorithms 
with Object-Oriented Design Patterns in C++</b><br>
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<H2><A NAME="SECTION0018210000000000000000">Pass By Value</A></H2>
<A NAME="seccpppassbyvalue">&#160;</A>
<P>
Consider a pair of C++ functions defined in Program&nbsp;<A HREF="page592.html#progcpp1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page592.html#progcpp1c"><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>.
The function <tt>One</tt> calls the function <tt>Two</tt>.
In general, every function call includes a (possibly empty) list of arguments.
The arguments specified in a function call are called
<em>actual parameters</em><A NAME=57152>&#160;</A>.
In this case, there is only one actual parameter--<tt>y</tt>.
<P>
<P><A NAME="57157">&#160;</A><A NAME="progcpp1c">&#160;</A> <IMG WIDTH=575 HEIGHT=238 ALIGN=BOTTOM ALT="program57154" SRC="img2599.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2599.gif"  ><BR>
<STRONG>Program:</STRONG> Example of Pass-By-Value Parameter Passing<BR>
<P>
<P>
The method by which the parameter is passed to a function is determined
by the function definition.
In this case, the function <tt>Two</tt> is defined as accepting
a single argument of type <tt>int</tt> called <tt>x</tt>.
The arguments which appear in a function definition are called
<em>formal parameters</em><A NAME=57164>&#160;</A>.
If the type of a formal parameter is <em>not</em> a reference
(see Section&nbsp;<A HREF="page590.html#seccppreference" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page590.html#seccppreference"><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>),
then the parameter passing method is <em>pass-by-value</em>.
<P>
The semantics of pass-by-value work like this:
The effect of the formal parameter definition is to create a local
variable of the specified type in the given function.
E.g., the function <tt>Two</tt> has a local variable of type <tt>int</tt>
called <tt>x</tt>.
When the function is called,
the <em>values</em> (<I>r</I>-values) of the <em>actual parameters</em> are used
to initialize the <em>formal parameters</em>
before the body of the function is executed.
<P>
Since the formal parameters give rise to local variables,
if a new value is assigned to a formal parameter,
that value has no effect on the actual parameters.
Therefore, the output obtained produced by the function <tt>One</tt>
defined in Program&nbsp;<A HREF="page592.html#progcpp1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page592.html#progcpp1c"><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> is:
<PRE>2
1</PRE>
<P>
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