Processing Form Data with PHP
CSCI 2910-001 In-Class Exercise

You should be able to...

This will be a rather short exercise, but it presents a major component of PHP: processing form data. Up to this point all we have done is generate HTML output using PHP code. Nice, but kinda boring. Now we will begin to generate HTML output using PHP code that is based on input from a user in the form of a form or URL. This is the first step in creating dynamic code.

There are two ways to pass data from a client's browser to the server:

• through an HTML form and
• as part of a URL (which is just like the get method of a form)

This lab will look at the methods for getting that data into your PHP scripts.

By the way, for those of you doing the reading, this material comes from the Williams and Lane book, Web database Applications with PHP and MySQL, pages 189 to 202.

Forms Refresher

Okay, so this is the second forms refresher this semester, but since the first one was over two months ago, I thought it might not be a bad idea to just hit the high points. Furthermore, we're going to have to make a table to play around with our PHP scripts anyway.

Just as with JavaScript, we are going to be accessing the form data using the names of the forms and each of their elements, so be sure to use the name/id attribute for all components of the form.

Remember that a form tag has three attributes:

• action
• method
• target

The attribute action specifies the program or URL that the form will be sent to. The attribute method tells the browser how to get the form data to the server applications. There are two values for this attribute: "get" and "post". Setting method to "get" sends the client's data as part of a URL just like you were typing the URL to a web site. (Note that this method is what we will be mimicking in order to send PHP data as part of a URL.)

Setting method to "post" sends the client's data to the server as part of a separate file.

Last of all, the target attribute tells the browser in which window to display the results or if a new browser window should be opened to display the server's response.

The table below is presented as a brief (incomplete) reference for the table elements. For a better reference, see Devguru's descriptions of the form tags input, select, and textarea.

Using a Form to Pass Data

We are going to take small steps toward the development of a PHP script designed to accept form data. The reason for this is that if we create a large piece of PHP code and try to run it all at one time, it will be very hard to debug using our PHP engine's limited capabilities for debugging. This is a good rule to follow whenever developing any type of code.

Now what we need to do is be able to get the text strings from the form inputs incorporated into our script. The data from a form is passed to the PHP script as part of an array. The form element's name is the argument for the array. For the method "post", the array name is $_POST while $_GET is the array name when the method "get" is used.

If we had wanted to do this same exercise using the method "get", all we would have had to do is replace the array $_POST with $_GET.

Other Types of Form Elements

Now let's see how form elements other than inputs of type "text"show up in the PHP arrays $_GET or $_POST.

Run this form multiple times to see how modifications in the entered values show up in the script. Be sure to execute the form both with a checkbox selected and with it not selected. In the case where the checkbox is not selected, that particular value does not show up in the PHP data. In other words, the client will only send data for checkboxes that are selected. This means that in your programs you will need to take special consideration for the code used to check checkboxes. It should be something like:

if ($_POST["check_value"] == "true")
     // insert code here for the "true" case
else
     // insert code here for the "off" case

There is no reason to test for a checkbox being off. It will never work. In addition, the value "true" is simply the value I used for the checkbox. If you used a different value for the checkbox, that will be sent to the script instead.

This matter of the checkbox data not being sent if nothing is checked becomes a real problem when the checkbox is the only form element. This means that there will be no $_POST or $_GET array since there will be no data at all. To avoid this, include a hidden element or name the submit button so at least some data is sent.

"multiple" Attribute for Select Input

A recent addition to the attributes of the select input is "multiple". It allows a client to select more than one element from a select/drop down box. The select box below uses this attribute. Holding the shift key or the ctrl key down when clicking options allows for multiple selections.

By the way, the code for the above selectbox is:

<select multiple="multiple" name="colors" >
    <option value="0">red</option>
    <option value="1">blue</option>
    <option value="2">green</option>
    <option value="3">pink</option>
    <option value="4">teal</option>
    <option value="5">other</option>
</select>

Although most designers opt for checkboxes when selecting more than one option, the option to allow for multiple selections from a select element adds an interesting facet to receiving form data. When PHP receives the values selected by the client, only the last value is visible. For example, if we were to do a print_r() of the data received from the above select box when red, blue, and pink were selected, the result would be:

Array ( [mult_example] => 3 )

where 3 is the value assigned to pink.

To avoid this, name the select element with a PHP array-styled name, e.g., colors[]. When the array is initialized, it will create an array of selected values for that form element. If we were to change the name of our select to "colors[]", we would get the following result from our print_r() function.

Array ( [colors] => Array ( [0] => 0 [1] => 1 [2] => 3 ) )

If needed for other form elements, the array-styled name can be used allowing subsequent form values to be included in an array.

Other Pre-Defined PHP Arrays

GET and POST information are not the only things that are available with arrays. You can access a number of blocks of information such as:

• Cookie variables in the array $_COOKIE.
• Environmental variables in the array $_ENV.
• Session variables in the array $_SESSION.
• Sever variables in the array $_SERVER.

Formatting a Form's Input

Now that we can receive input from a form, let's make sure it is formatted properly. The in-class exercise from the lecture asked us to use the string functions to filter, refine, and pull apart strings using the functions:

• strtolower()
• strtoupper()
• ucfirst()
• ucwords()
• trim()
• rtrim()
• ltrim()
• substr()
• strpos()
• substr_replace()

Using these functions, create a simple form with two text inputs, one for a phone number and one for an e-mail address, and a textarea to input a string. Use as the action of the form the URL "http://einstein.etsu.edu/~zabc123/strings.php" where zabc123 is your user name. Next, using the PHP template, create a script that will:

• extract and output the area code from the phone number;
• extract and output the user name in lower case from the e-mail address;
• count the number of times that the letter 't' appears in the string;
• find every '&' and replace with "&amp" in the string;
• output the string in sentence case capitalizing the first letter and verifying that all of the other letters are lower case; and
• output the string in title case capitalizing the first letter of each word and verifying that all of the other letters are lower case.

Developed by David Tarnoff for his students in CSCI 2910 at ETSU