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checking the information from HTML forms October 1, 2008

b4 u use the values in your script, u need to check the variables to make sure they contain what u expect ‘em to contain! Thus never trust info from user.

Checking for empty fields:

u can require the user to enter info in a field and check when the user didn’t and let him back to re-fill that field using:

empty($_POST['field_name']);

this function returns true if the field is empty,,, false otherwise !

Checking for specific format:

u can check using some built in functions like if u expect string, u can check using is_string and so on… for a table of these functions c this previous post Changing the order of statement execution

Using regular expressions to check user input:

u can aslo compare the info to a pattern to c if it matches if u care a lot about the information pattern using ereg function … for more in this ,,, check this previous post: pattern matching with regular expressions

Cleaning information:

• strip_tags: this function removes all tags from the text, u can keep some tags:

$variable_name = strip_tags($_POST)['field_name'],”<tag u allow> <tag u allow>“);

• htmlspecialchars: this function changes some special characters to HTML into HTML format that allow ‘em to display without any special meaning

Examples: < become &alt;

? become &gt;

and & become &amp;

$variable_name= htmlspecialchars($_POST)['field_name']);

• trim: remove extra spaces at the beginning and the end of the field info, bcz it’s familiar that user enter spaces by mistake.

$variable_name= trim($_POST)['field_name']);

Example:

in this example, i will use the same forms in the previous post but i will check for three fields (first name, second name and last name) not to keep blank ,,, if so … the user will be asked to re-fill ‘em …. if they r not blank , then it will output the same information in that example….

Building the forms code:

<br><center><h2> Customer information </h2></center>
<br><br>

<center>
<table border=”0″>
<form action=”customer_info.php” method=”POST”>
<tr> <td> First name:</td> <td> <input type=”text” name=”first_name”></td></tr>
<tr> <td>Second name: </td> <td> <input type=”text” name=”second_name”> </td></tr>
<tr><td>Last name: </td> <td> <input type=”text” name=”last_name”></td> </tr>
<tr><td> Street Address:</td><td> <input type=”text” name=”st_address”></td> </tr>
<tr><td> City:</td><td>
<select name=”city”
<option> Amman </option>
<option> Aqaba </option>
<option> Irbd </option>
<option> Zarqa </option>
</td> </tr>
<tr><td>Sex: </td><td>
<input type =”radio” name=”Radio1″ value= “M” > Male
<input type =”radio” name=”Radio1″ value= “F”> Female
</td></tr>
<tr><td>Your Operating system: </td><td>
<input type= “checkbox” name=”os0″ value=”W”> Windows
<input type= “checkbox” name=”os1″ value=”L”> Linux
<input type= “checkbox” name=”os2″ value=”M”> Mac
</td></tr>
</table><br>

<input type=”submit” value=”submit name”>
</form>

the customer info code:

<?php

function set_sex(){
if ($_POST[Radio1]==”M”) {
$sex= “Male”;
}
else
{
$sex= “Female”;}
}

function print_info()
{

echo “Welcome “,$_POST['first_name'],”!<br>”;
echo “Your second name is: “,$_POST['second_name'];
echo “<br>Your last name is: “,$_POST['last_name'];
echo “<br>”;
echo “you are “, $sex;
echo ” living in: “, $_POST[city];
echo “  in the “, $_POST[st_address],” Street”;
echo “<br>and your operating systems are: <br>”;

if (isset($_POST['os0'])) {
echo “Windows<br>”;
}

if (isset($_POST['os1'])) {
echo “Linux<br>”;
}

if (isset($_POST['os2'])) {
echo “Mac<br>”;
}
return;
}

function blank_check(){
if (empty($_POST['first_name']))
{
echo “You didn’t enter your first name! <br>”;
$blank_check_var = TRUE;
}

if (empty($_POST['second_name']))
{
echo “You didn’t enter your second name! <br>”;
$blank_check_var = TRUE;
}

if (empty($_POST['last_name']))
{
echo “You didn’t enter your last name! <br>”;
$blank_check_var = TRUE;
}

return $blank_check_var;

}

//main
set_sex();
$check_var= blank_check();
if (!$check_var){
print_info();
}

?>

The output after leaving the first name blank is:

You didn’t enter your first name!

The output after leaving the first and second name blank is:

You didn’t enter your first name!
You didn’t enter your second name!

The output after leaving the first, second and last name blank is:

You didn’t enter your first name!
You didn’t enter your second name!
You didn’t enter your last name!