Validating String Data

Many of the string functions covered in Chapter 3 can be used to

produce strings with consistent formatting. Regular expression func-

tions are some of the best tools for verifying that string data meets

the strict formatting required for e-mail addresses, Web page URLs,

or date values. In Chapter 3, you used regular expressions in suc-

cessive examples to continually refine the requirements of an e-mail

address and to isolate strings that were not in the correct format.

Strings are often not formatted as expected. The user may enter

spaces before or after a text entry, or magic quotes may add escape

characters before a single or double quotation mark. In this chapter

and the previous one, you have been introduced to two functions that

will assist in cleaning up posted data: the stripslashes() function,

which removes the leading slashes for escape sequences in strings;

and the trim() function, which removes any leading or trailing white

space from a string.

For example, the following function ensures that the entered field,

passed as the $data parameter, is a telephone number in the form

###-###-####:

function validatePhoneNumber($data, $fieldName) {

global $errorCount;

201

Handling Multiple Errors

A common but poor programming practice is to stop processing a

form when an error is found and display the error to the user. The

user corrects the error, only to find that another field in the form

is also filled out incorrectly. For a large and complex form, this can

result in multiple attempts before a form is processed successfully.

A better practice is to record the error, usually in an array, and con-

tinue processing the form. This allows the script to display a complete

list of all the errors found. Users can then go back and correct all of

the errors at one time.

Handling User Input

To validate the input of the Scholarship.html form:

1.

Return to the process_Scholarship.php document in your

text editor.

Add a new function, displayRequired(). This function

accepts one argument, $fieldName, which is the name of the

field as it appears on the Web form. This function displays an

error message.

function displayRequired($fieldName) {

echo "The field \"$fieldName\" is required.<br />n";

2.

202

3.

Add a second new function called validateInput() below

the displayRequired() function. This function takes two

parameters. The first parameter, $data, is a string to be vali-

dated. The second parameter, $fieldName, is the name of the

form field. The function returns the $data parameter after it

has been cleaned up. Notice that the function uses the global

variable $errorCount.

function validateInput($data, $fieldName) {

global $errorCount;

4.

Immediately after the validateInput() function, declare and

initialize a new variable called $errorCount as follows:

$errorCount = 0;

5.

Modify the assignment statements for the $firstName

and $lastName variables to receive the output of the

validateInput() function:

$firstName = validateInput($_POST['fName'],

"First name");

$lastName = validateInput($_POST['lName'],

"Last name");

6.

Add a conditional statement immediately after the value

of $lastName has been assigned. This statement will either

display the total number of errors or a “Thank you” message if

there were no errors.

if ($errorCount>0)

echo "Please use the \"Back\" button to

7.

8.

Save the document and upload it to the Web server.

Open the Scholarship.html page in the Web browser by enter-

ing the following URL: http://<yourserver>/PHP_Projects/

Chapter.04/Chapter/Scholarship.html.

Attempt to submit the form to the process_Scholarship.php

form handler without entering any data for the first or last

name fields. You should see the result shown in Figure 4-7,

with two error messages.

203

9.

Figure 4-7

Empty input with form validation

10. Close the Web browser window.

Redisplaying the Web Form

In the previous example, error messages were displayed after you vali-

dated the data input on the form. However, when you went back to

the form, you needed to rekey the information in the form controls.

A better option would be to redisplay the form with the controls set

to the values that the user entered the last time the form was submit-

ted. As a result, the user only has to enter data for fields that were left

empty or did not contain a valid response. The user does not have to

retype data that was entered correctly the first time. This type of form

is often called a sticky form.

To redisplay the Web form, you need to add the XHTML form ele-

ments to the output of the PHP script. Because the Web form only

needs to be redisplayed if there was an error in the Web form valida-

tion, the code to output the Web form should be part of the error-

handling section of the script. The code to redisplay the Web form

can go into a function for convenience in isolating that part of the

code from the remainder of the script.

Handling User Input

204

The most convenient way to embed large portions of XHTML code

within a PHP script is to use advanced escaping from XHTML. When

you insert a PHP script section, you are escaping from XHTML. With

advanced escaping, you close one PHP script section, insert some

XHTML elements, and then open another PHP script section to con-

tinue the script. Any XHTML code between the two script sections

is considered output, as it would have been using an echo or print

statement. You have already seen some simple examples of advanced

escaping in Chapter 1, where multiple PHP script sections appeared

in a single PHP script.

If the closing tag for the first PHP script section is within a function

or the control block for a conditional structure, the XHTML code will

only be displayed when the function is called or the conditional con-

trol block is executed. If the closing tag for the first PHP script section

is within the control block of a looping structure, the XHTML code

will be displayed with each iteration of the loop.

The following code declares a function named ShowHomePageLink().

The function displays an image and a message, both of which are

hyperlinks to index.php. This function could have been coded as a

series of echo or print statements, but it is much easier to read using

advanced escaping.

function ShowHomePageLink() {

?>

When you

The following exercise illustrates how to redisplay the Web form.

Advanced escaping from XHTML will be used to display the Web

form. Additionally, the Web form will be a sticky form, keeping the

values of the fields that were entered correctly.

To redisplay the Web form within the process_Scholarship.php script:

1.

2.

Reopen the process_Scholarship.php script in your editor.

Add the following function to redisplay the Web form:

function redisplayForm($firstName, $lastName) {

?>

<h2 style = "text-align:center">Scholarship Form</h2>

<form name="scholarship" action="process_

Scholarship.php"

method="post">

<p>First Name: <input type="text" name="fName"

value="<?php echo $firstName; ?>" /></p>

<p>Last Name: <input type="text" name="lName"

value="<?php echo $lastName; ?>" /></p>

<p><input type="reset" value="Clear Form" /> 

 <input type="submit" name="Submit" value="Send

Form" />

</form>

<?php

}

This code is

205

3.

Modify the if clause of the final if. . .else statement to call

the redisplayForm() function if there were errors. Add the

text shown in bold below:

if ($errorCount>0) {

echo "Please re-enter the information below.<br />\n";

4.

5.

Save the document and upload it to the Web server.

Open the Scholarship.html page in the Web browser by enter-

ing the following URL: http://<yourserver>/PHP_Projects/

Chapter.04/Chapter/Scholarship.html.

Attempt to submit the form without entering any data for one

of the two fields. You should see a result similar to that shown

in Figure 4-8, with one error message and the Web form with

the value you entered automatically reinserted into the same

field. Enter data for the empty field and resubmit the form to

see the “Thank you” message.

6.

Figure 4-8

7.

The error message with the redisplayed sticky form

Close your Web browser window.

The mail()

Handling User Input

Using the Submitted Data

Once the data entered into the Web form is validated, it needs to be

used. Exactly how the data is used varies depending on the purpose

of the form. In some cases, information can be written to or queried

from a database. In other cases, a file can be downloaded to the user.

In this section, the data from the Web form will be used to generate

an e-mail message and display a confirmation message for the user.

206

E-mailing the Web Form

In PHP, an e-mail message is sent using the mail() function. The basic

syntax for this function is mail(recipient(s), subject, message).

The value you assign to the recipient(s) argument is a string

of one or more e-mail addresses in the standard format for an

“Address Specifier”, as defined by the Internet Message Format