Hoofdstuk 50. Using PHP

PHP offers many predefined variables, like the superglobal $_POST. You may loop through $_POST as it's an associate array of all POSTed values. For example, let's simply loop through it with foreach, check for empty() values, and print them out.

<?php
$empty = $post = array();
foreach ($_POST as $varname => $varvalue) {
    if (empty($varvalue)) {
        $empty[$varname] = $varvalue;
    } else {
        $post[$varname] = $varvalue;
    }
}

print "<pre>";
if (empty($empty)) {
    print "None of the POSTed values are empty, posted:\n";
    var_dump($post);
} else {
    print "We have " . count($empty) . " empty values\n";
    print "Posted:\n"; var_dump($post);
    print "Empty:\n";  var_dump($empty);
    exit;
}
?>

The function addslashes() will do this. See also mysql_escape_string(). You may also strip backslashes with stripslashes().

The PHP function stripslashes() will strip those backslashes from your string. Most likely the backslashes magically exist because the PHP directive magic_quotes_gpc is on.

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 return() the value, not echo() it.

In PHP, the ending for a block of code is either "?>" or "?>\n" (where \n means a newline). So in the example above, the echoed sentences will be on one line, because PHP omits 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.

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.

The functions header(), setcookie (), and the session functions need to add headers to the output stream but headers can only be sent before all other content. There can be no output before using these functions, output such as HTML. The function headers_sent() will check if your script has already sent headers and see also the Output Control functions.

The getallheaders() 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:

<?php
$headers = getallheaders();
foreach ($headers as $name => $content) {
    echo "headers[$name] = $content<br>\n";
}
?>

See also apache_lookup_uri(), apache_response_headers(), and fsockopen()

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: and the manual section on HTTP Authentication .

Netscape is more strict regarding html tags (such as tables) then IE. Running your html output through a html validator, such as , might be helpful. For example, a missing </table> might cause this.

Also, both IE and Lynx ignore any NULs (\0) 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. In *nix, pipe it through od -c and look for any \0 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.

In order to embed <?xml straight into your PHP code, you'll have to turn off short tags by having the PHP directive short_open_tags set to 0. You cannot set this directive with ini_set(). Regardless of short_open_tags being on or off, you can do something like: <?php echo '<?xml'; ?>. The default for this directive is on.

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 <% and %> 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 asp_tags php.ini variable, or use the appropriate Apache directive.

Read the manual page on predefined variables as it includes a partial list of predefined variables available to your script. A complete list of available variables (and much more information) can be seen by calling the phpinfo() function. Be sure to read the manual section on variables from outside of PHP as it describes common scenerios for external variables, like from a HTML form, a Cookie, and the URL.

It's important to realize that the PHP directive register_globals also affects server and environment variables. When register_globals = off (the default is off since PHP 4.2.0), $DOCUMENT_ROOT will not exist. Instead, use $_SERVER['DOCUMENT_ROOT'] . If register_globals = on then the variables $DOCUMENT_ROOT and $GLOBALS['DOCUMENT_ROOT'] will also exist.

If you're sure register_globals = on and wonder why $DOCUMENT_ROOT isn't available inside functions, it's because these are like any other variables and would require global $DOCUMENT_ROOT inside the function. See also the manual page on variable scope. It's preferred to code with register_globals = off.