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<TITLE>The Copy Constructor, Parameter Passing
and Function Return Values</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="SECTION0018323000000000000000">The Copy Constructor, Parameter Passing
and Function Return Values</A></H3>
<P>
The copy constructor plays a special r&#244;le
in pass-by-value parameter passing.
As discussed in Section&nbsp;<A HREF="page592.html#seccpppassbyvalue" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page592.html#seccpppassbyvalue"><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 semantics of pass-by-value stipulate that the
the values of the actual parameters are used
to <em>initialize</em> the formal parameters when a function is called.
The compiler achieves this by using the copy constructor
to copy the value of the actual parameter to the formal parameter.
<P>
The copy constructor plays a similar r&#244;le
when a value is returned from a function using the <tt>return</tt> statement.
The copy constructor is used to copy the value
from the called function back to the point
where the calling function makes use of the result.
<P>
Program&nbsp;<A HREF="page599.html#progcomplex1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page599.html#progcomplex1c"><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> gives an implementation for the copy
constructor of the <tt>Complex</tt> class.
The copy constructor initializes the
the member variables <tt>real</tt> and <tt>imag</tt>
by calling explicitly their respective copy constructors (line&nbsp;14).
After the member variables have been initialized,
the body of the constructor runs.
In this case, the body of the copy constructor is empty (line&nbsp;15).
<P>
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