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<HTML><!-- -- Copyright (c) 1996-1999 -- Silicon Graphics Computer Systems, Inc. -- -- Permission to use, copy, modify, distribute and sell this software -- and its documentation for any purpose is hereby granted without fee, -- provided that the above copyright notice appears in all copies and -- that both that copyright notice and this permission notice appear -- in supporting documentation. Silicon Graphics makes no -- representations about the suitability of this software for any -- purpose. It is provided "as is" without express or implied warranty. -- -- Copyright (c) 1994 -- Hewlett-Packard Company -- -- Permission to use, copy, modify, distribute and sell this software -- and its documentation for any purpose is hereby granted without fee, -- provided that the above copyright notice appears in all copies and -- that both that copyright notice and this permission notice appear -- in supporting documentation. Hewlett-Packard Company makes no -- representations about the suitability of this software for any -- purpose. It is provided "as is" without express or implied warranty. -- --><Head><Title>Trivial Iterator</Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--end header--><BR Clear><H1>Trivial Iterator</H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "iterators.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "concept.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: iterators</TD><TD Align=right VAlign=top><b>Component type</b>: concept</TD></TR></Table><h3>Description</h3>A Trivial Iterator is an object that may be dereferenced to refer tosome other object. Arithmetic operations (such as increment andcomparison) are not guaranteed to be supported.<h3>Refinement of</h3><A href="Assignable.html">Assignable</A>,<A href="EqualityComparable.html">Equality Comparable</A>,<A href="DefaultConstructible.html">Default Constructible</A><h3>Associated types</h3><Table border><TR><TD VAlign=top>Value type</TD><TD VAlign=top>The type of the value obtained by dereferencing a Trivial Iterator</TD></tr></table><h3>Notation</h3><Table><TR><TD VAlign=top><tt>X</tt></TD><TD VAlign=top>A type that is a model of Trivial Iterator</TD></TR><TR><TD VAlign=top><tt>T</tt></TD><TD VAlign=top>The value type of <tt>X</tt></TD></TR><TR><TD VAlign=top><tt>x</tt>, <tt>y</tt></TD><TD VAlign=top>Object of type <tt>X</tt></TD></TR><TR><TD VAlign=top><tt>t</tt></TD><TD VAlign=top>Object of type <tt>T</tt></TD></tr></table><h3>Definitions</h3>A type that is a model of Trivial Iterator may be <i>mutable</i>,meaning that the values referred to by objects of that type may bemodified, or <i>constant</i>, meaning that they may not. For example,<tt>int*</tt> is a mutable iterator type and <tt>const int*</tt> is aconstant iterator type. If an iterator type is mutable, this impliesthat its value type is a model of<A href="Assignable.html">Assignable</A>; the converse, though, is notnecessarily true.<P>A Trivial Iterator may have a <i>singular</i> value, meaning that theresults of most operations, including comparison for equality, areundefined. The only operation that a is guaranteed to be supported isassigning a nonsingular iterator to a singular iterator.<P>A Trivial Iterator may have a <i>dereferenceable</i> value, meaningthat dereferencing it yields a well-defined value. Dereferenceableiterators are always nonsingular, but the converse is not true. Forexample, a null pointer is nonsingular (there are well definedoperations involving null pointers) even thought it is notdereferenceable.<P><i>Invalidating</i> a dereferenceable iterator means performing anoperation after which the iterator might be nondereferenceable orsingular. For example, if <tt>p</tt> is a pointer, then <tt>deletep</tt> invalidates <tt>p</tt>.<h3>Valid expressions</h3>In addition to the expressions defined in<A href="Assignable.html">Assignable</A>,<A href="EqualityComparable.html">Equality Comparable</A>, and <A href="DefaultConstructible.html">Default Constructible</A>, thefollowing expressions must be valid.<Table border><TR><TH>Name</TH><TH>Expression</TH><TH>Type requirements</TH><TH>Return type</TH></TR><TR><TD VAlign=top>Default constructor</TD><TD VAlign=top><tt>X x</tt></TD><TD VAlign=top> </TD><TD VAlign=top> </TD></TR><TR><TD VAlign=top>Dereference</TD><TD VAlign=top><tt>*x</tt></TD><TD VAlign=top> </TD><TD VAlign=top>Convertible to <tt>T</tt> <A href="#1">[1]</A></TD></TR><TR><TD VAlign=top>Dereference assignment</TD><TD VAlign=top><tt>*x = t</tt></TD><TD VAlign=top><tt>X</tt> is mutable</TD><TD VAlign=top> </TD></TR><TR><TD VAlign=top>Member access</TD><TD VAlign=top><tt>x->m</tt> <A href="#2">[2]</A></TD><TD VAlign=top><tt>T</tt> is a type for which <tt>x.m</tt> is defined</TD><TD VAlign=top> </TD></tr></table><h3>Expression semantics</h3><Table border><TR><TH>Name</TH><TH>Expression</TH><TH>Precondition</TH><TH>Semantics</TH><TH>Postcondition</TH></TR><TR><TD VAlign=top>Default constructor</TD><TD VAlign=top><tt>X x</tt></TD><TD VAlign=top> </TD><TD VAlign=top> </TD><TD VAlign=top><tt>x</tt> is singular</TD></TR><TR><TD VAlign=top>Dereference</TD><TD VAlign=top><tt>*x</tt></TD><TD VAlign=top><tt>x</tt> is dereferenceable</TD><TD VAlign=top> </TD><TD VAlign=top> </TD></TR><TR><TD VAlign=top>Dereference assignment</TD><TD VAlign=top><tt>*x = t</tt></TD><TD VAlign=top><tt>x</tt> is dereferenceable</TD><TD VAlign=top> </TD><TD VAlign=top><tt>*x</tt> is a copy of t</TD></TR><TR><TD VAlign=top>Member access</TD><TD VAlign=top><tt>x->m</tt></TD><TD VAlign=top><tt>x</tt> is dereferenceable</TD><TD VAlign=top>Equivalent to <tt>(*x).m</tt></TD><TD VAlign=top> </TD></tr></table><h3>Complexity guarantees</h3>The complexity of operations on trivial iterators isguaranteed to be amortized constant time.<h3>Invariants</h3><Table border><TR><TD VAlign=top>Identity</TD><TD VAlign=top><tt>x == y</tt> if and only if <tt>&*x == &*y</tt></TD></tr></table><h3>Models</h3><UL><LI>A pointer to an object that is not part of an array.</UL><h3>Notes</h3><P><A name="1">[1]</A>The requirement for the return type of <tt>*x</tt> is specified as"convertible to <tt>T</tt>", rather than simply <tt>T</tt>,because it sometimes makes sense for an iterator to return some sortof proxy object instead of the object that the iterator conceptuallypoints to. Proxy objects are implementation details rather than partof an interface (one use of them, for example, is to allow an iteratorto behave differently depending on whether its value is being read orwritten), so the value type of an iterator that returns a proxy isstill <tt>T</tt>.<P><A name="2">[2]</A>Defining <tt>operator-></tt> for iterators depends on a feature that is partof the C++ language but that is not yet implemented by all C++compilers. If your compiler does not yet support this feature, theworkaround is to use <tt>(*it).m</tt> instead of <tt>it->m</tt>.<h3>See also</h3><A href="InputIterator.html">Input Iterator</A>, <A href="OutputIterator.html">Output Iterator</A>, <A href="ForwardIterator.html">Forward Iterator</A>,<A href="BidirectionalIterator.html">Bidirectional Iterator</A>, <A href="RandomAccessIterator.html">Random Access Iterator</A>,<A href="Iterators.html">Iterator Overview</A><!-- start footer --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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