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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. 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It is provided "as is" without express or implied warranty. -- --><Head><Title>stack<T, Sequence></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>stack<T, Sequence></H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "containers.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left><Img src = "adaptors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right></TD></TR><TR><TD Align=left VAlign=top><b>Categories</b>: containers, adaptors</TD><TD Align=right VAlign=top><b>Component type</b>: type</TD></TR></Table><h3>Description</h3>A <tt>stack</tt> is an adaptor that provides a restricted subset of<A href="Container.html">Container</A> functionality: it provides insertion, removal, andinspection of the element at the top of the stack. <tt>Stack</tt> is a"last in first out" (LIFO) data structure: the element at the top of a <tt>stack</tt> is the one that was most recently added. <A href="#1">[1]</A><tt>Stack</tt> does not allow iteration through its elements. <A href="#2">[2]</A><P><tt>Stack</tt> is a container adaptor, meaning that it is implemented ontop of some underlying container type. By default that underlyingtype is <tt><A href="Deque.html">deque</A></tt>, but a different type may be selected explicitly.<h3>Example</h3><pre>int main() { stack<int> S; S.push(8); S.push(7); S.push(4); assert(S.size() == 3); assert(S.top() == 4); S.pop(); assert(S.top() == 7); S.pop(); assert(S.top() == 8); S.pop(); assert(S.empty());}</pre><h3>Definition</h3>Defined in the standard header <A href="stack">stack</A>, and in the nonstandardbackward-compatibility header <A href="stack.h">stack.h</A>.<h3>Template parameters</h3><Table border><TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR><TR><TD VAlign=top><tt>T</tt></TD><TD VAlign=top>The type of object stored in the stack.</TD><TD VAlign=top> </TD></TR><TR><TD VAlign=top><tt>Sequence</tt></TD><TD VAlign=top>The type of the underlying container used to implement the stack.</TD><TD VAlign=top><tt><A href="Deque.html">deque</A><T></tt></TD></tr></table><h3>Model of</h3><A href="Assignable.html">Assignable</A>, <A href="DefaultConstructible.html">Default Constructible</A><h3>Type requirements</h3><UL><LI><tt>T</tt> is a model of <A href="Assignable.html">Assignable</A>.<LI><tt>Sequence</tt> is a model of <A href="BackInsertionSequence.html">Back Insertion Sequence</A>.<LI><tt>Sequence::value_type</tt> is the same type as <tt>T</tt>.<LI>If <tt>operator==</tt> is used, then <tt>T</tt> is a model of <A href="EqualityComparable.html">Equality Comparable</A><LI>If <tt>operator<</tt> is used, then <tt>T</tt> is a model of <A href="LessThanComparable.html">LessThan Comparable</A>.</UL><h3>Public base classes</h3>None.<h3>Members</h3><Table border><TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>value_type</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>size_type</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>stack()</tt></TD><TD VAlign=top> <A href="DefaultConstructible.html">Default Constructible</A></TD><TD VAlign=top>The default constructor. Creates an empty <tt>stack</tt>.</TD></TR><TR><TD VAlign=top><tt>stack(const stack&)</tt></TD><TD VAlign=top> <A href="Assignable.html">Assignable</A></TD><TD VAlign=top>The copy constructor.</TD></TR><TR><TD VAlign=top><tt>stack& operator=(const stack&)</tt></TD><TD VAlign=top> <A href="Assignable.html">Assignable</A></TD><TD VAlign=top>The assignment operator.</TD></TR><TR><TD VAlign=top><tt>bool empty() const</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>size_type size() const</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>value_type& top()</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>const value_type& top() const</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>void push(const value_type&)</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>void pop()</tt> <A href="#3">[3]</A></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>bool operator==(const stack&, const stack&)</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>bool operator<(const stack&, const stack&)</tt></TD><TD VAlign=top><tt>stack</tt></TD><TD VAlign=top>See below.</TD></tr></table><h3>New members</h3>These members are not defined in the <A href="Assignable.html">Assignable</A> and <A href="DefaultConstructible.html">Default Constructible</A>requirements, but are specific to <tt>stack</tt>.<Table border><TR><TH>Member</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>value_type</tt></TD><TD VAlign=top>The type of object stored in the <tt>stack</tt>. This is the same as <tt>T</tt> and <tt>Sequence::value_type</tt>.</TD></TR><TR><TD VAlign=top><tt>size_type</tt></TD><TD VAlign=top>An unsigned integral type. This is the same as <tt>Sequence::size_type</tt>.</TD></TR><TR><TD VAlign=top><tt>bool empty() const</tt></TD><TD VAlign=top>Returns <tt>true</tt> if the <tt>stack</tt> contains no elements, and <tt>false</tt> otherwise. <tt>S.empty()</tt> is equivalent to <tt>S.size() == 0</tt>.</TD></TR><TR><TD VAlign=top><tt>size_type size() const</tt></TD><TD VAlign=top>Returns the number of elements contained in the <tt>stack</tt>.</TD></TR><TR><TD VAlign=top><tt>value_type& top()</tt></TD><TD VAlign=top>Returns a mutable reference to the element at the top of the stack. Precondition: <tt>empty()</tt> is <tt>false</tt>.</TD></TR><TR><TD VAlign=top><tt>const value_type& top() const</tt></TD><TD VAlign=top>Returns a const reference to the element at the top of the stack. Precondition: <tt>empty()</tt> is <tt>false</tt>.</TD></TR><TR><TD VAlign=top><tt>void push(const value_type& x)</tt></TD><TD VAlign=top>Inserts <tt>x</tt> at the top of the stack. Postconditions: <tt>size()</tt> will be incremented by <tt>1</tt>, and <tt>top()</tt> will be equal to <tt>x</tt>.</TD></TR><TR><TD VAlign=top><tt>void pop()</tt></TD><TD VAlign=top>Removes the element at the top of the stack. <A href="#3">[3]</A> Precondition: <tt>empty()</tt> is <tt>false</tt>. Postcondition: <tt>size()</tt> will be decremented by <tt>1</tt>.</TD></TR><TR><TD VAlign=top><tt>bool operator==(const stack&, const stack&)</tt></TD><TD VAlign=top>Compares two stacks for equality. Two stacks are equal if they contain the same number of elements and if they are equal element-by-element. This is a global function, not a member function.</TD></TR><TR><TD VAlign=top><tt>bool operator<(const stack&, const stack&)</tt></TD><TD VAlign=top>Lexicographical ordering of two stacks. This is a global function, not a member function.</TD></tr></table><h3>Notes</h3><P><A name="1">[1]</A>Stacks are a standard data structure, and are discussed in allalgorithm books. See, for example, section 2.2.1 of Knuth.(D. E. Knuth, <i>The Art of ComputerProgramming. Volume 1: Fundamental Algorithms</i>, second edition. Addison-Wesley, 1973.)<P><A name="2">[2]</A>This restriction is the only reason for <tt>stack</tt> to exist at all.Note that any <A href="FrontInsertionSequence.html">Front Insertion Sequence</A> or <A href="BackInsertionSequence.html">Back Insertion Sequence</A> can be used as a stack; in the case of <A href="Vector.html">vector</A>, forexample, the stack operations are the member functions <tt>back</tt>,<tt>push_back</tt>, and <tt>pop_back</tt>. The only reason to use the containeradaptor <tt>stack</tt> instead is to make it clear that you are performingonly stack operations, and no other operations.<P><A name="3">[3]</A>One might wonder why <tt>pop()</tt> returns <tt>void</tt>, instead of <tt>value_type</tt>.That is, why must one use <tt>top()</tt> and <tt>pop()</tt> to examine and removethe top element, instead of combining the two in a single memberfunction? In fact, there is a good reason for this design. If <tt>pop()</tt> returned the top element, it would have to return by valuerather than by reference: return by reference would create a danglingpointer. Return by value, however, is inefficient: it involves atleast one redundant copy constructor call. Since it is impossible for<tt>pop()</tt> to return a value in such a way as to be both efficientand correct, it is more sensible for it to return no value at all andto require clients to use <tt>top()</tt> to inspect the value at the top ofthe stack.<h3>See also</h3><tt><A href="queue.html">queue</A></tt>, <tt><A href="priority_queue.html">priority_queue</A></tt>, <A href="Container.html">Container</A>, <A href="Sequence.html">Sequence</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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