Title	:	Maintaining State
	Author	:	SS
	Class	:	NavMar
	Content	:


<P>
	<B>Maintaining State</B>
<P>
<UL>

	<LI><A HREF="self_referential_scripts.ht">Self-referential</A>
	scripts are very cool 
	and extremely common.  However, they do introduce some 
	complexities to your application.

<P>

	<LI>One of the most subtle problems 
	introduced by self-referential scripts is the fact that since 
	<A HREF="/Internet/Protocols/HTTP/">HTTP</A> is a stateless 
	protocol,
	a <A HREF="/Authoring/CGI">CGI</A> script has no memory of 
	previous connections.  Thus, if you want to refer back to a 
	script for a second, the data from the first refernce will be 
	lost.
	
<P>

	<LI>However, you can programmatically give 
	your CGI script memory by saving state in the form of hidden form 
	variables.

<P>

	<LI>In other words, you will make sure that 
	all of the form data from one request gets passed to following 
	requests via the HIDDEN form tag.

<P>

	<LI>Consider the following code which does 
	just this:

<P>

<PRE>
#!/usr/local/bin/perl
require "cgi-lib.pl";
&#38;ReadParse(*form_data);
print "Content-type: text/html\n\n";

		// Print out form if this is the 
		// users's first request.  You've seen 
		// this already!

if ($form_data{'submit'} eq "")
  {
  print qq!
  &lt;HTML&gt;
  &lt;HEAD&gt;
  &lt;TITLE&gt;Testing Form Input&lt;/TITLE&gt;
  &lt;/HEAD&gt;
  &lt;BODY&gt;
  &lt;FORM METHOD = "POST" 
		ACTION = "self-refer.cgi"&gt;
  &lt;CENTER&gt;
  &lt;TABLE BORDER = "1"&gt;
  &lt;TR&gt;
  &lt;TH&gt;First Name&lt;/TH&gt;
  &lt;TD&gt;&lt;INPUT TYPE = "text" 
		NAME = "f_name"&gt;&lt;/TD&gt;
  &lt;/TR&gt;
    
  &lt;TR&gt;
  &lt;TH&gt;Last Name&lt;/TH&gt;
  &lt;TD&gt;&lt;INPUT TYPE = "text" 
		NAME = "l_name"&gt;&lt;/TD&gt;
  &lt;/TR&gt;
  
  &lt;TR&gt;
  &lt;TH&gt;Email&lt;/TH&gt;
  &lt;TD&gt;&lt;INPUT TYPE = "text" 
		NAME = "email"&gt;&lt;/TD&gt;
  &lt;/TR&gt;
     
  &lt;/TABLE&gt;
  &lt;P&gt;
  &lt;INPUT TYPE = "SUBMIT" NAME = "submit" 
		VALUE = "submit"&gt;
  &lt;/CENTERv
  &lt;/FORM&gt;
  &lt;/BODY&gt;
  &lt;/HTML&gt;!;
  exit;
  }

		// If the user has entered 
		// only first name,
		// last name and email, let's 
		// get phone number
		// to. But we must make sure 
		// that we save the
		// values for first nme, last 
		// name and email
		// as hidden form tags.

elsif ($form_data{'submit'} eq "submit")
  {
  print qq!
  &lt;HTML&gt;   
  &lt;HEAD&gt;
  &lt;TITLE&gt;Get More Data While 
		Remembering Old&lt;/TITLE&gt;
  &lt;/HEAD&gt;
  &lt;BODY&gt;
  You submitted the following information:
  &lt;P&gt;
  &lt;TABLE BORDER = "1"&gt;!;
  
  foreach $key (keys(%form_data))
    {
    print qq!
    &lt;TR&gt;
    &lt;TD&gt;$key&lt;/TD&gt;
    &lt;TD&gt;$form_data{$key}&lt;/TD&gt;
    &lt;/TR&gt;!;
    }
  
		// Here is where we ask for the 
		// phone number
  print qq!
  &lt;/TABLE&gt;
  &lt;P&gt;
  Thank you very much.  However, we need 
  one more bit of information.
  Please input your phone number below:
  &lt;P&gt;
  &lt;FORM METHOD = "POST" ACTION = "self-refer.cgi"v
  &lt;INPUT TYPE = "TEXT" NAME = "phone"&gt;!;

		// Here is were we add the 
		// hidden variables.
		// Note that we do not want to 
		// keep the value
		// for "submit" cause we are 
		// going to create a
 		// new submit button with a new 
		// VALUE argument 
		// so that we know which request 
		// is coming in.
  
  foreach $key (keys(%form_data))
    {
    if ($key ne "submit")
      {
      print qq!
      &lt;INPUT TYPE = "HIDDEN" NAME = "$key" 
                VALUE = "$form_data{$key}"&gt;!;
      }
    }
   
  print qq!
  &lt;INPUT TYPE = "SUBMIT" NAME = "submit" 
            VALUE = "Final Submit"&gt;
  &lt;/FORM&gt;
  &lt;/BODY&gt;
  &lt;/HTML&gt;!;
  }

		// If the user clicked a 
		// button with "Final Submit" 
		// then the above routines 
		// would have both returned 
		// false and we can assume that 
		// the user has entered the 
		// phone number, so we handle it.
  
else 
  {
  print qq!
  &lt;HTML&gt;
  &lt;HEAD&gt;
  &lt;TITLE&gt;Testing Form Input&lt;/TITLE&gt;
  &lt;/HEAD&gt;
  &lt;BODY&gt;
  &lt;TABLE&gt;!;
    
  foreach $key (keys(%form_data))
  {
  print qq!
  &lt;TR&gt;
  &lt;TD&gt;$key&lt;/TD&gt;
  &lt;TD&gt;$form_data{$key}&lt;/TD&gt;
  &lt;/TR&gt;!;
  }  
  
  print qq!
  &lt;/TABLE&gt;
  &lt;/BODY&gt;
  &lt;/HTML&gt;!;
  }    
</PRE>

</UL>
<P>
	<H3>Additional Resources:</H3>
	<UL>
	<LI><A HREF="/Authoring/Languages/Perl/">Perl </A>
	<LI><A HREF="/Authoring/Languages/Perl/Resources.html">Perl Resources </A>
	<LI><A HREF="http://www.extropia.com/books/instant_web_scripts/index.html">Instant Web Scripts With CGI</A>
	</UL>
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