php-doc-en/faq/using.xml

<?xml encoding="iso-8859-1"?>
<!-- $Revision: 1.5 $ -->
<chapter id="faq.using">
  <title>Using PHP</title>
  <titleabbrev>Using PHP</titleabbrev>

   <para>
    This section gathers most common errors that occur at 
    build time.
   </para>

  <qandaset>
   <qandaentry id="faq.using.anyform">
    <question>
     <para>
      I would like to write a generic PHP script that can handle data coming 
      from any form. How do I know which POST method variables are available?
     </para>
    </question>
    <answer>
     <para>
      Make sure that the track_vars feature is
      enabled in your php3.ini file.    If you compiled PHP with
      &quot;--enable-track-vars&quot; it will be on by default.
      Alternatively you can enable it at run-time on a per-script
      basis by putting &lt;?php_track_vars?&gt; at the top of your file.
      When track_vars is on, it creates three associative arrays.
      $HTTP_GET_VARS, $HTTP_POST_VARS and $HTTP_COOKIE_VARS.  So, to
      write a generic script to handle POST method variables you would
      need something similar to the following:
      <programlisting>
    while (list($var, $value) = each($HTTP_POST_VARS)) {
        echo "$var = $value&lt;br&gt;\n";
    }
      </programlisting>
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.singlequotes">
    <question>
     <para>
      I need to convert all single-quotes (') to a backslash 
      followed by a single-quote. How can I do this with a 
      regular expression?
     </para>
    </question>
    <answer>
     <para>
      First off, take a look at the <function>addslashes()</function>
      function. It will do exactly what you want.  You should also have
      a look at the <link linkend="ini.magic-quotes-gpc">magic_quotes_gpc</link> 
      directive in your <filename>php.ini</filename> file.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.wrong_order">
    <question>
     <para>
      When I do the following, the output is printed in 
      the wrong order: 
     <programlisting>
      function myfunc($argument) {
        echo $argument + 10;
      }
      $variable = 10;
      echo "myfunc($variable) = " . myfunc($variable);
    </programlisting>
     what's going on?
     </para>
    </question>
    <answer>
     <para>
      To be able to use the results of your function in an expression (such
      as concatenating it with other strings in the example above), you need
      to <emphasis>return</emphasis> the value, not <function>echo</function> 
      it.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.newlines">
    <question>
     <para>
      Hey, what happened to my newlines?
     <programlisting>
&lt;PRE&gt;
  1 &lt;?echo $result[1];?&gt;
  2 &lt;?echo $result[2];?&gt;
    </programlisting>
     </para>
    </question>
    <answer>
     <para>
      In PHP, the ending for a block of code is either "?&gt;" or
      "?&gt;\n" (where \n means a newline). This means that you need to
      insert an extra newline after each block of PHP code in the above
      example.
     </para>
     <para>
      Why does PHP do this? Because when formatting normal HTML, this
      usually makes your life easier because you don't want that newline,
      but you'd have to create extremely long lines or otherwise make the
      raw page source unreadable to achieve that effect.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.header">
    <question>
     <para>
      I need to access information in the request header directly. 
      How can I do this?
     </para>
    </question>
    <answer>
     <para>
      The <function>getallheaders</function> function will do this if 
      you are running PHP as a module.  So, the following bit of code 
      will show you all the request headers:
     <programlisting>
    $headers = getallheaders();
    for(reset($headers); $key = key($headers); next($headers)) {
        echo "headers[$key] = ".$headers[$key]."&lt;br&gt;\n";
    }
     </programlisting>
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.authentication">
    <question>
     <para>
      When I try to use authentication with IIS I get 'No Input file specified'.
     </para>
    </question>
    <answer>
     <para>
    The security model of IIS is at fault here. This is a problem
    common to all CGI programs running under IIS.  A workaround is
    to create a plain HTML file (not parsed by php) as the entry page
    into an authenticated directory.  Then use a META tag to redirect
    to the PHP page, or have a link to the PHP page.  PHP will
    then recognize the authentication correctly.  When the ISAPI
    module is ready, this will no longer be a problem.  This should
    not effect other NT web servers.  For more information, see: 
    <ulink url="&faqurl.iis;">&faqurl.iis;</ulink>.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.PHP-IIS">
    <question>
     <para>
      I've followed all the instructions, but still can't 
      get PHP and IIS to work together!
     </para>
    </question>
    <answer>
     <para>
      Make sure any user who needs to run a PHP script has the rights
      to run <filename>php.exe</filename>!  IIS uses an anonymous user which is added at the
      time IIS is installed.  This user needs rights to <filename>php.exe</filename>. 
      Also, any authenticated user will also need rights to execute 
      <filename>php.exe</filename>.  And for IIS4 you need to tell it
      that PHP is a script engine.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.netscape">
    <question>
     <para>
      My PHP script works on IE and Lynx, but on Netscape some of
      my output is missing. When I do a "View Source" I see the 
      content in IE but not in Netscape.
     </para>
    </question>
    <answer>
     <para>
      Very good question!  ;)  This is a tricky little issue and it has come up 
      twice in the past month as of this writing.  Both times I ended up 
      spending a good 20 minutes trying to figure out what the heck was going
      on.  The answer is that both IE and Lynx ignore any NULs
      (<literal>\0</literal>) in the HTML stream.  Netscape does not.
      The best way to check for this is to compile the command-line version
      of PHP (also known as the CGI version) and run your script from the
      command line and pipe it through 'od -c' and look for any 
      <literal>\0</literal> characters.  (If you are on Windows you need to 
      find an editor or some other program that lets you look at binary files)
      When Netscape sees a NUL in a file it will typically not output 
      anything else on that line whereas both IE and Lynx will.  If this
      issue has bitten you, congratulations!  You are not alone.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.mixml">
    <question>
     <para>
      How am I supposed to mix XML and PHP? It complains 
      about my &lt;?xml&gt; tags!
     </para>
    </question>
    <answer>
     <para>
     You need to turn off the short tags by setting short_tags to 0 in your
     <filename>php.ini</filename> file, or by using the php3_short_tags Apache
     directive. (You could even use a &lt;File&gt; section to do this
     selectively.) You can also disable and re-enable the short tags 
     in your script using the short_tags() function.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.editor">
    <question>
     <para>
      How can I use PHP with FrontPage or Dreamweaver or some 
      other HTML editor that insists on moving my code around?
     </para>
    </question>
    <answer>
     <para>
      One of the easiest things to do is to enable using ASP tags in your
      PHP code. This allows you to use the ASP-style &lt;% and %&gt; code
      delimiters. Most of the popular HTML editors handle those more
      intelligently (for now). To enable the ASP-style tags, you need
      to set the asp_tags <filename>php.ini</filename> variable, or use the 
      <link linkend="ini.asp-tags">asp_tags</link> Apache directive.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.variables">
    <question>
     <para>
      Where can I find a complete list of pre-set variables available 
      to me, and why are these not documented in the PHP documentation?
     </para>
    </question>
    <answer>
     <para>
      The best way is to stick a &lt;?phpinfo()?&gt; tag on a page and 
      load it up.  This will show you all sorts of information about your
      PHP setup, including a list of both environment variables and also
      special variables set by your web server.  This list can't really be
      documented in the PHP documentation because it will change from one
      server to another.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.mysql">
    <question>
     <para>
      Why do I get an error that looks something like this: 
      "Warning: 0 is not a MySQL result index in &lt;file&gt; 
      on line &lt;x&gt;" or "Warning: Supplied argument is not 
      a valid MySQL result resource in &lt;file&gt; on line &lt;x&gt;?
     </para>
    </question>
    <answer>
     <para>
      You are trying to use a result identifier that is 0.  The 0 indicates
      that your query failed for some reason.  You need to check for errors
      after submitting a query and before you attempt to use the returned 
      result identifier.  The proper way to do this is with code similar
      to the following:
      <programlisting>
        $result = mysql_query("select * from tables_priv");
        if(!$result) {
            echo mysql_error();
            exit;
        }
      </programlisting>
      or
      <programlisting>
        $result = mysql_query("select * from tables_priv")
                    or die("Bad query: ".mysql_error());
      </programlisting>
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.form-image">
    <question>
     <para>
      I'm trying to use an &lt;input type="image"&gt; tag, but 
      the $foo.x and $foo.y variables aren't available. 
      Where are they?
     </para>
    </question>
    <answer>
     <para>
      When submitting a form, it is possible to use an image instead of
      the standard submit button with a tag like:
      <programlisting>
&lt;input type="image" SRC="image.gif" NAME="foo"&gt;
      </programlisting>
      When the user clicks somewhere on the image, the accompanying form
      will be transmitted to the server with two additional variables:
      foo.x and foo.y.
     </para>
     <para>
      Because $foo.x and $foo.y are invalid variable names in PHP, they are
      automagically converted to $foo_x and $foo_y.  That is, the periods
      are replaced with underscores.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.select-multiple">
    <question>
     <para>
      How do I get all the results from a SELECT MULTIPLE HTML tag? 
     </para>
    </question>
    <answer>
     <para>
      The SELECT MULTIPLE tag in an HTML construct allows users to select multiple
      items from a list.  These items are then passed to the action handler for the 
      form. The problem is that they are all passed with the same widget name. ie.
      <programlisting>
      &lt;SELECT NAME="var" MULTIPLE&gt;
      </programlisting>
      Each selected option will arrive at the action handler as:
      <programlisting>
   var=option1
   var=option2
   var=option3
      </programlisting>
      Each option will overwrite the contents of the previous $var variable. The
      solution is to use PHP's 
      non-indexed array feature. The following should be used:
      <programlisting>
&lt;SELECT NAME="var[]" MULTIPLE&gt;
      </programlisting>
      This tells PHP to treat <varname>var</varname> as an array and each assignment of a
      value to var[] adds an item to the array. The first item becomes 
      <varname>$var[0]</varname>, the next <varname>$var[0]</varname>, etc. 
      The <function>count</function> function can be used to determine how 
      many options were selected, and the <function>sort</function> function can be 
      used to sort  the option array if necessary.
     </para>
     <para>
      Note that if you are using JavaScript the <literal>[]</literal> on the element name
      might cause you problems when you try to refer to the element by name.  
      Use it's numerical form element id instead, or enclose the
      variable name in single quotes and use that as the index to the
      elements array, for example:
      <programlisting>
variable = documents.forms[0].elements['var[]'];
      </programlisting>
     </para>
    </answer>
   </qandaentry>
  </qandaset>
 </chapter>

 <!-- Keep this comment at the end of the file
 Local variables:
 mode: sgml
 sgml-omittag:t
 sgml-shorttag:t
 sgml-minimize-attributes:nil
 sgml-always-quote-attributes:t
 sgml-indent-step:1
 sgml-indent-data:t
 sgml-parent-document:nil
 sgml-default-dtd-file:"../../manual.ced"
 sgml-exposed-tags:nil
 sgml-local-catalogs:nil
 sgml-local-ecat-files:nil
 End:
 -->