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Sticky fields, and preventing injection attacks
Sticky fields and session example from a Well House Consultants training course
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This example is described in the following article(s):
   • Easy conversion - image formats, currencies and distances - [link]

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Source code: fru2.php Module: H301

# Function - re-usable code.
# "If you want to cut and paste, you should use a function instead"

# Data values from file or once only!

$imperial = array("inches" => 1.0"feet" => 12.0,
"yards" => 36.0"miles" => 1760.0 36 );
$metric = array ("millimetres" => 1.0"centimetres" => 10.0,
"metres" => 1000.0"kilometres" => 1000000.0);

# DEFINE you function before you use it ;-)

function selector($name,$possibilities,$current="") {
# variables like $retst and $poss not seen outside
        # That allows these working to be a hidden black box
$retst "<select name=\"$name\">";
$poss explode("|",$possibilities);
        foreach (
$poss as $thisun) {
$setto "";
                if (
$current == $thisun$setto " SELECTED";
$retst .= "<option value=\"$thisun\"$setto>$thisun</option>";
$retst .= "</select>";
# copy $retst back into whatever is done with the result
return $retst;

bounce($val) {
        return (

grabunits($source) {
        return (

# We can now use that code several times over!

$oldunits selector("old",grabunits($imperial),$_REQUEST[old]);
$newunits selector("new",grabunits($metric),$_REQUEST["new"]);

if (
$_REQUEST[amount]) { # We have some data!
        # Flexibiity in mind - can POST or GET to this.

        # Should validate that it's a number and that units are good

$inches $_REQUEST[amount] * $imperial[$_REQUEST[old]];
$newval $inches 25.4;
$newval /= $metric[$_REQUEST["new"]];

# Avoid injection attacks in the echo
        # Remember people COULD modify the source
$message bounce($_REQUEST[amount])." ".
bounce($_REQUEST[old]). " converts to $newval".

} else {

$message "Convert Imperial to Metric lengths";



<h1>Unit Selector - from old to new</h1>

<b><?= $message ?></b><br><br>

Convert from <?= $oldunits ?> to <?= $newunits ?><br>
amount <input name="amount" value="<?= bounce($_REQUEST[amount]) ?>">
and <input type=submit>


Learn about this subject
This module and example are covered on our public PHP Techniques course. If you have a group of three or more trainees who need to learn the subject, we can also arrange a private or on site course for you.

Books covering this topic
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Other Examples
This example comes from our "Sticky fields and session" training module. You'll find a description of the topic and some other closely related examples on the "Sticky fields and session" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
• Our Solutions centre provides a number of longer technical articles.
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This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

Web site author
This web site is written and maintained by Well House Consultants.

Conditions of use
Past attendees on our training courses are welcome to use individual examples in the course of their programming, but must check the examples they use to ensure that they are suitable for their job. Remember that some of our examples show you how not to do things - check in your notes. Well House Consultants take no responsibility for the suitability of these example programs to customer's needs.

This program is copyright Well House Consultants Ltd. You are forbidden from using it for running your own training courses without our prior written permission. See our page on courseware provision for more details.

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