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 <H2>6.3 Example Program: An Inventory System</H2>
 <A NAME="idx119"><!></A>
 <A NAME="idx120"><!></A>
 <P>Let's use a simple inventory management system to illustrate the use of several <B><I><A HREF="../stdlibref/list.html">list</A></I></B> operations. Assume a business, named <I>WorldWideWidgetWorks</I>, requires a software system to manage their supply of widgets. </P>
 <BLOCKQUOTE><HR><B>
 NOTE -- The complete version of the widget works program is in file widwork.cpp.
 </B><HR></BLOCKQUOTE>
 <P>Widgets are simple devices, distinguished by different identification numbers:</P>

 <UL><PRE>
 class  Widget {
 public:
   Widget(int a = 0) : id(a) { }
   void operator=(const Widget&amp; rhs) { id = rhs.id; }
   int id;
   friend std::ostream&amp; operator&lt;&lt;
     (std::ostream&amp; out, const Widget&amp; w)
     { return out &lt;&lt; "Widget " &lt;&lt; w.id; }
 };

 bool operator== (const Widget&amp; lhs, const Widget&amp; rhs) {
   return lhs.id == rhs.id;
 }

 bool operator&lt; (const Widget&amp; lhs, const Widget&amp; rhs) {
   return lhs.id &lt; rhs.id;
 }
 </PRE></UL>
 <P>The state of the inventory is represented by two <B><I><A HREF="../stdlibref/list.html">list</A></I></B>s: a <B><I>list</I></B> of widgets represents the stock of widgets on hand, and a <B><I>list</I></B> of widget identification types represents the type of widgets that customers have backordered. </P>

 <UL><PRE>
 typedef std::list&lt;Widget, std::allocator&lt;Widget&gt; &gt; widgetList;
 typedef std::list&lt;int, std::allocator&lt;int&gt; &gt;       idList;
 </PRE></UL>
 <P>To handle our inventory we have two commands: <SAMP>order()</SAMP> processes orders, and <SAMP>receive()</SAMP> processes the shipment of a new widget.</P>

 <UL><PRE>
 class inventory {
 public:
   void order (int wid);   // process order for widget type wid
   void receive (int wid); // receive widget of type wid
                           // in shipment
 private:
   widgetList on_hand;
   idList     on_order;
 };
 </PRE></UL>
 <P>When a new widget arrives in shipment, we compare the widget identification number with the list of widget types on backorder. We use <SAMP>find()</SAMP> to search the backorder list, immediately shipping the widget if necessary. Otherwise it is added to the stock on hand:</P>

 <UL><PRE>
 void inventory::receive (int wid) {
   std::cout &lt;&lt; "Received shipment of widget type "
             &lt;&lt; wid &lt;&lt; std::endl;

   idList::iterator weneed =
     find(on_order.begin(), on_order.end(), wid);

   if (weneed != on_order.end()) {
     std::cout &lt;&lt; "Ship " &lt;&lt; Widget(wid)
               &lt;&lt; " to fill back order" &lt;&lt; std::endl;
     on_order.erase(weneed);
   }
   else
     on_hand.push_front(Widget(wid));
 }
 </PRE></UL>
 <A NAME="idx121"><!></A>
 <P>When a customer orders a new widget, we scan the list of widgets in stock to determine if the order can be processed immediately. We can use the standard algorithm <SAMP>std::find_if()</SAMP> to search the list. To do so, we need a binary function that takes as its argument a widget and determines whether the widget matches the type requested. We create this function by taking a general binary widget-testing function, and binding the second argument to the specific widget type. To use the function <SAMP>std::bind2nd()</SAMP>, however, requires that the binary function be an instance of the class <B><I><A HREF="../stdlibref/binary-function.html">binary_function</A></I></B>. The general widget-testing function is written as follows:</P>

 <UL><PRE>
 struct WidgetTester : std::binary_function&lt;Widget, int, bool&gt; {

 public:
   bool operator()(const Widget&amp; wid, int testid) const
   {
     return wid.id == testid;
   }

 };
 </PRE></UL>
 <P>The widget order function is then written as follows:</P>

 <UL><PRE>
 void inventory::order(int wid) {

   std::cout &lt;&lt; "Received order for widget type " &lt;&lt; wid
             &lt;&lt; std::endl;

   widgetList::iterator wehave =
     std::find_if(on_hand.begin(), on_hand.end(),
                  std::bind2nd(WidgetTester(), wid));

     if (wehave != on_hand.end()) {
       std::cout &lt;&lt; "Ship " &lt;&lt; *wehave &lt;&lt; std::endl;
       on_hand.erase(wehave);
    }
    else {
      std::cout &lt;&lt; "Back order widget of type "  &lt;&lt; wid
                &lt;&lt; std::endl;
      on_order.push_front(wid);
    }

 }
 </PRE></UL>

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	distributed under the License is distributed on an "AS IS" BASIS,
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	<HTML>
	<HEAD>
	<TITLE>Example Program: An Inventory System</TITLE>
	<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
	<BODY BGCOLOR=#FFFFFF>
	<A HREF="6-2.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="7.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library User's Guide</B></DIV>
	<H2>6.3 Example Program: An Inventory System</H2>
	<A NAME="idx119"><!></A>
	<A NAME="idx120"><!></A>
	<P>Let's use a simple inventory management system to illustrate the use of several <B><I><A HREF="../stdlibref/list.html">list</A></I></B> operations. Assume a business, named <I>WorldWideWidgetWorks</I>, requires a software system to manage their supply of widgets. </P>
	<BLOCKQUOTE><HR><B>
	NOTE -- The complete version of the widget works program is in file widwork.cpp.
	</B><HR></BLOCKQUOTE>
	<P>Widgets are simple devices, distinguished by different identification numbers:</P>

	<UL><PRE>
	class Widget {
	public:
	Widget(int a = 0) : id(a) { }
	void operator=(const Widget& rhs) { id = rhs.id; }
	int id;
	friend std::ostream& operator<<
	(std::ostream& out, const Widget& w)
	{ return out << "Widget " << w.id; }
	};

	bool operator== (const Widget& lhs, const Widget& rhs) {
	return lhs.id == rhs.id;
	}

	bool operator< (const Widget& lhs, const Widget& rhs) {
	return lhs.id < rhs.id;
	}
	</PRE></UL>
	<P>The state of the inventory is represented by two <B><I><A HREF="../stdlibref/list.html">list</A></I></B>s: a <B><I>list</I></B> of widgets represents the stock of widgets on hand, and a <B><I>list</I></B> of widget identification types represents the type of widgets that customers have backordered. </P>

	<UL><PRE>
	typedef std::list<Widget, std::allocator<Widget> > widgetList;
	typedef std::list<int, std::allocator<int> > idList;
	</PRE></UL>
	<P>To handle our inventory we have two commands: <SAMP>order()</SAMP> processes orders, and <SAMP>receive()</SAMP> processes the shipment of a new widget.</P>

	<UL><PRE>
	class inventory {
	public:
	void order (int wid); // process order for widget type wid
	void receive (int wid); // receive widget of type wid
	// in shipment
	private:
	widgetList on_hand;
	idList on_order;
	};
	</PRE></UL>
	<P>When a new widget arrives in shipment, we compare the widget identification number with the list of widget types on backorder. We use <SAMP>find()</SAMP> to search the backorder list, immediately shipping the widget if necessary. Otherwise it is added to the stock on hand:</P>

	<UL><PRE>
	void inventory::receive (int wid) {
	std::cout << "Received shipment of widget type "
	<< wid << std::endl;

	idList::iterator weneed =
	find(on_order.begin(), on_order.end(), wid);

	if (weneed != on_order.end()) {
	std::cout << "Ship " << Widget(wid)
	<< " to fill back order" << std::endl;
	on_order.erase(weneed);
	}
	else
	on_hand.push_front(Widget(wid));
	}
	</PRE></UL>
	<A NAME="idx121"><!></A>
	<P>When a customer orders a new widget, we scan the list of widgets in stock to determine if the order can be processed immediately. We can use the standard algorithm <SAMP>std::find_if()</SAMP> to search the list. To do so, we need a binary function that takes as its argument a widget and determines whether the widget matches the type requested. We create this function by taking a general binary widget-testing function, and binding the second argument to the specific widget type. To use the function <SAMP>std::bind2nd()</SAMP>, however, requires that the binary function be an instance of the class <B><I><A HREF="../stdlibref/binary-function.html">binary_function</A></I></B>. The general widget-testing function is written as follows:</P>

	<UL><PRE>
	struct WidgetTester : std::binary_function<Widget, int, bool> {

	public:
	bool operator()(const Widget& wid, int testid) const
	{
	return wid.id == testid;
	}

	};
	</PRE></UL>
	<P>The widget order function is then written as follows:</P>

	<UL><PRE>
	void inventory::order(int wid) {

	std::cout << "Received order for widget type " << wid
	<< std::endl;

	widgetList::iterator wehave =
	std::find_if(on_hand.begin(), on_hand.end(),
	std::bind2nd(WidgetTester(), wid));

	if (wehave != on_hand.end()) {
	std::cout << "Ship " << *wehave << std::endl;
	on_hand.erase(wehave);
	}
	else {
	std::cout << "Back order widget of type " << wid
	<< std::endl;
	on_order.push_front(wid);
	}

	}
	</PRE></UL>

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