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<H2>queue</H2>
<P><B>Library:</B>&nbsp;&nbsp;<A HREF="2-7.html">Containers</A></P>

<PRE><HR><B><I>Does not inherit</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Interface</A></LI>
<LI><A HREF="#sec6">Constructors</A></LI>
<LI><A HREF="#sec7">Member Functions</A></LI>
<LI><A HREF="#sec8">Nonmember Operators</A></LI>
<LI><A HREF="#sec9">Example</A></LI>
<LI><A HREF="#sec10">See Also</A></LI>
<LI><A HREF="#sec11">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
<H4>Members</H4>
<UL><TABLE CELLPADDING=3>
<TR><TD VALIGN=top>
<A HREF="#idx1112">back()</A><BR>
<A HREF="#idx1114">empty()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx1115">front()</A><BR>
<A HREF="#idx1117">pop()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx1118">push()</A><BR>
<A HREF="#idx1111">queue()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx1119">size()</A><BR>
</TD></TR>
</TABLE></UL>
<H4>Non-Members</H4>
<UL><TABLE CELLPADDING=3>
<TR><TD VALIGN=top>
<A HREF="#idx1121">operator!=()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx1123">operator&gt;()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx1122">operator&lt;()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx1120">operator==()</A><BR>
</TD></TR>
</TABLE></UL>

<A NAME="sec2"><H3>Summary</H3></A>
<P>A container adaptor that behaves like a queue (first in, first out)</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;queue&gt;

namespace std {
  template &lt;class T, class Container = deque&lt;T&gt; &gt; 
  class queue;
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <B><I>queue</I></B> container adaptor lets a container act as a queue. In a queue, items are pushed into the back of the container and removed from the front. The first items pushed into the queue are the first items to be popped off of the queue (first in, first out, or FIFO). </P>
<P><B><I>queue</I></B> can adapt any container that supports the <SAMP>front()</SAMP>, <SAMP>back()</SAMP>, <SAMP>push_back()</SAMP>, and <SAMP>pop_front()</SAMP> operations. In particular, <B><I><A HREF="deque.html">deque</A></I></B> and <B><I><A HREF="list.html">list</A></I></B> can be used. </P>
<A NAME="sec5"><H3>Interface</H3></A>

<UL><PRE>namespace std {

  template &lt;class T, class Container = deque&lt;T&gt; &gt;
  class queue {

    public:

      // typedefs
      typedef typename Container::value_type value_type;
      typedef typename Container::size_type size_type;
      typedef Container container_type;

      // Construct/Copy/Destroy
      explicit queue (const Container&amp; = Container());

      // Accessors
      bool empty () const;
     size_type size () const;
     value_type&amp; front ();
     const value_type&amp; front () const;
     value_type&amp; back ();
     const value_type&amp; back () const;
     void push (const value_type&amp;);
     void pop ();
  };

  // Nonmember Operators

  template &lt;class T, class Container&gt;
  bool operator==(const queue&lt;T, Container&gt;&amp;,
                  const queue&lt;T, Container&gt;&amp;);

  template &lt;class T, class Container&gt;
  bool operator!=(const queue&lt;T, Container&gt;&amp;,
                  const queue&lt;T, Container&gt;&amp;);

  template &lt;class T, class Container&gt;
  bool operator&lt;(const queue&lt;T, Container&gt;&amp;,
                 const queue&lt;T, Container&gt;&amp;);

  template &lt;class T, class Container&gt;
  bool operator&gt;(const queue&lt;T, Container&gt;&amp;,
                 const queue&lt;T, Container&gt;&amp;);

  template &lt;class T, class Container&gt;
  bool operator&lt;=(const queue&lt;T, Container&gt;&amp;,
                  const queue&lt;T, Container&gt;&amp;);

  template &lt;class T, class Container&gt;
  bool operator&gt;=(const queue&lt;T, Container&gt;&amp;,
                  const queue&lt;T, Container&gt;&amp;);
}
</PRE></UL>
<A NAME="sec6"><H3>Constructors</H3></A>

<A NAME="idx1111"></A><PRE>explicit <B>queue</B>(const Container&amp; = Container());</PRE>
<UL>
<P>Creates a queue of zero elements.</P>
</UL>

<A NAME="sec7"><H3>Member Functions</H3></A>

<A NAME="idx1112"></A><PRE>value_type&amp; 
<B>back</B>();</PRE>
<UL>
<P>Returns a reference to the item at the back of the queue (the last item pushed into the queue).</P>
</UL>


<A NAME="idx1113"></A><PRE>const value_type&amp; 
<B>back</B>() const;</PRE>
<UL>
<P>Returns a constant reference to the item at the back of the queue as a <SAMP>const_value_type</SAMP>.</P>
</UL>


<A NAME="idx1114"></A><PRE>bool 
<B>empty</B>() const;</PRE>
<UL>
<P>Returns <SAMP>true</SAMP> if the queue is empty, otherwise <SAMP>false</SAMP>.</P>
</UL>


<A NAME="idx1115"></A><PRE>value_type&amp; 
<B>front</B>();</PRE>
<UL>
<P>Returns a reference to the item at the front of the queue.</P>
</UL>


<A NAME="idx1116"></A><PRE>const value_type&amp; 
<B>front</B>() const;</PRE>
<UL>
<P>Returns a constant reference to the item at the front of the queue as a <SAMP>const_value_type</SAMP>.</P>
</UL>


<A NAME="idx1117"></A><PRE>void 
<B>pop</B>();</PRE>
<UL>
<P>Removes the item at the front of the queue.</P>
</UL>


<A NAME="idx1118"></A><PRE>void 
<B>push</B>(const value_type&amp; x);</PRE>
<UL>
<P>Pushes <SAMP>x</SAMP> onto the back of the queue.</P>
</UL>


<A NAME="idx1119"></A><PRE>size_type 
<B>size</B>() const;</PRE>
<UL>
<P>Returns the number of elements on the queue.</P>
</UL>

<A NAME="sec8"><H3>Nonmember Operators</H3></A>

<A NAME="idx1120"></A><PRE>template &lt;class T, class Container&gt;
  bool <B>operator==</B>(const queue&lt;T, Container&gt;&amp; x,
                   const queue&lt;T, Container&gt;&amp; y);</PRE>
<UL>
<P>   Returns <SAMP>true</SAMP> if <SAMP>x</SAMP> is the same as <SAMP>y</SAMP>.</P>
</UL>


<A NAME="idx1121"></A><PRE>template &lt;class T, class Container&gt;
  bool <B>operator!=</B>(const queue&lt;T, Container&gt;&amp; x,
                   const queue&lt;T, Container&gt;&amp; y);</PRE>
<UL>
<P>   Returns <SAMP>!(x==y)</SAMP>.</P>
</UL>


<A NAME="idx1122"></A><PRE>template &lt;class T, class Container&gt;
  bool <B>operator&lt;</B>(const queue&lt;T, Container&gt;&amp; x,
                  const queue&lt;T, Container&gt;&amp; y);</PRE>
<UL>
<P>Returns <SAMP>true</SAMP> if the queue defined by the elements contained in <SAMP>x</SAMP> is lexicographically less than the queue defined by the elements contained in <SAMP>y</SAMP>.</P>
</UL>


<A NAME="idx1123"></A><PRE>template &lt;class T, class Container&gt;
  bool <B>operator&gt;</B>(const queue&lt;T, Container&gt;&amp; x,
                  const queue&lt;T, Container&gt;&amp; y);</PRE>
<UL>
<P>Returns <SAMP>y &lt; x</SAMP>.</P>
</UL>


<A NAME="idx1124"></A><PRE>template &lt;class T, class Container&gt;
  bool <B>operator&lt;</B>(const queue&lt;T, Container&gt;&amp; x,
                  const queue&lt;T, Container&gt;&amp; y);</PRE>
<UL>
<P>Returns <SAMP>!(y &lt; x)</SAMP>.</P>
</UL>


<A NAME="idx1125"></A><PRE>template &lt;class T, class Container&gt;
  bool <B>operator&lt;</B>(const queue&lt;T, Container&gt;&amp; x,
                  const queue&lt;T, Container&gt;&amp; y);</PRE>
<UL>
<P>Returns <SAMP>!(x &lt; y)</SAMP>.</P>
</UL>

<A NAME="sec9"><H3>Example</H3></A>

<UL><PRE>//
//  queue.cpp
//

#include &lt;deque&gt;      // for deque
#include &lt;iostream&gt;   // for cout, endl
#include &lt;list&gt;       // for list
#include &lt;queue&gt;      // for queue
#include &lt;string&gt;     // for string


int main ()
{
    typedef std::queue&lt;int, std::list&lt;int, 
                                      std::allocator&lt;int&gt; &gt; &gt;
            IQueue;

    // Make a queue using a deque container.
    IQueue q;

    // Push a couple of values on and retrieve them.
    q.push (1);
    q.push (2);

    std::cout &lt;&lt; q.front () &lt;&lt; std::endl;
    std::cout &lt;&lt; q.back () &lt;&lt; std::endl;

    typedef std::queue&lt;std::string, std::deque&lt;std::string,
                       std::allocator&lt;std::string&gt; &gt; &gt; SQueue;

    // Make a queue of strings using a deque container.
    SQueue qs;

    // Push on a few strings then pop them back off.
    for (int i = 0; i &lt; 10; i++) {
        qs.push (std::string (i + 1, 'a'));
        std::cout &lt;&lt; qs.front () &lt;&lt; std::endl;
    }

    for (int j = 0; j &lt; 10; j++) {
        std::cout &lt;&lt; qs.front () &lt;&lt; std::endl;
        qs.pop ();
    }

    // Return 0 if both containers are empty, 
    // a non-zero value otherwise.
    return !(2 == q.size () &amp;&amp; qs.empty ());
}


Program Output:
</PRE></UL>
<UL><PRE>1
2
a
a
a
a
a
a
a
a
a
a
a
aa
aaa
aaaa
aaaaa
aaaaaa
aaaaaaa
aaaaaaaa
aaaaaaaaa
aaaaaaaaaa
</PRE></UL>
<A NAME="sec10"><H3>See Also</H3></A>
<P><B><I><A HREF="allocator.html">allocator</A></I></B>, <A HREF="containers.html">Containers</A>, <B><I><A HREF="priority-queue.html">priority_queue</A></I></B></P>
<A NAME="sec11"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 23.2.3.1</I></P>

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