php-doc-en/faq/using.xml

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<chapter id="faq.using">
  <title>Using PHP</title>
  <titleabbrev>Using PHP</titleabbrev>

  <para>
   This section gathers most common errors you can
   face, while writing PHP scripts.
  </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 <link linkend="ini.track-vars">track_vars</link>
      feature is enabled in your <filename>php.ini</filename>
      file. Since PHP 4.0.3, this feature is always on. When
      <literal>track_vars</literal> is on, it creates some
      associative arrays, the most important here is:
      <literal>$HTTP_POST_VARS</literal>. So, to write a generic
      script to handle POST method variables you would
      need something similar to the following:
      <programlisting role="php">
<![CDATA[
foreach ($HTTP_POST_VARS as $var => $value) {
    echo "$var = $value<br>\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 role="php">
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 role="php">
<![CDATA[
<pre>
<?php echo "This should be the first line."; ?>
<?php echo "This should show up after the new line above."; ?>
</pre>
]]>
      </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). So in the example above,
      the echoed sentences will be on one line, because PHP ommits
      the newlines after the block ending. This means that you need to
      insert an extra newline after each block of PHP code to make
      it print out one newline.
     </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.headers-sent">
    <question>
     <para>
      I get the message 'Warning: Cannot send session cookie - headers already
      sent...' or 'Cannot add header information - headers already sent...'.
     </para>
    </question>
    <answer>
     <para>
      The functions <function>header</function>,
      <function>set_cookie</function> and the session functions need to add
      headers to the output stream. Headers can only be sent before all other
      content.  function will do this if 
      you are running PHP as an Apache module. So, the following bit
      of code will show you all the request headers:
      <programlisting role="php">
<![CDATA[
$headers = getallheaders();
foreach ($headers as $name => $content) {
    echo "headers[$name] = $content<br>\n";
}
]]>
      </programlisting>
     </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 an Apache module. So, the following bit
      of code will show you all the request headers:
      <programlisting role="php">
<![CDATA[
$headers = getallheaders();
foreach ($headers as $name => $content) {
    echo "headers[$name] = $content<br>\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. With the ISAPI
      module, this is not 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.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>
      Netscape is more strict regarding html tags (such as tables) then 
      IE.  Running your html output through a html validator, such as 
      <ulink url="&faqurl.w3.validator;">validator.w3.org</ulink>, might 
      be helpful.  For example, a missing &lt;/table&gt; might cause this.
     </para>
     <para>
      Also, 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 <link linkend="commandline">command line</link> version of 
      PHP (also known as the CGI version) and run your script from the
      command line.  In *nix, pipe it through <literal>od -c</literal> 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. 
     </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
      <link linkend="ini.short-open-tag">short_tags</link> to 0 in your
      <filename>php.ini</filename> file, or by using the appropriate
      Apache directive. You could even use a &lt;File&gt; section to
      do this selectively.
     </para>
    </answer>
   </qandaentry>

   <qandaentry id="faq.using.editor">
    <question>
     <para>
      How can I use PHP with FrontPage 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. Some of the popular HTML editors handle those more
      intelligently (for now). To enable the ASP-style tags, you need
      to set the <link linkend="ini.asp-tags">asp_tags</link>
      <filename>php.ini</filename> variable, or use the 
      appropriate 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 <literal>&lt;?php phpinfo(); ?&gt;</literal>
      part 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.cgi-vars">
    <question>
     <para>
      I'm trying to access one of the standard CGI
      variables (such as $DOCUMENT_ROOT or $HTTP_REFERER) in a user-defined
      function, and it can't seem to find it. What's wrong?
     </para>
    </question>
    <answer>
     <para>
      Environment variables are normal global variables, so you must
      either declare them as global variables in your function (by using
      "<literal>global $DOCUMENT_ROOT;</literal>", for example) or by using
      the global variable array (ie, "<literal>$GLOBALS["DOCUMENT_ROOT"]</literal>".
     </para>
    </answer>
   </qandaentry>

  </qandaset>
 </chapter>

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