Podręcznik PHP
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Rozdział 50. PHP and HTML

PHP and HTML interact a lot: PHP generate HTML, and HTML has informations that will be sent to PHP.

1. What encodings/decodings do I need when I pass a value on via a form? And via an URL?
2. I'm trying to use an <input type="image"> tag, but the $foo.x and $foo.y variables aren't available. Where are they?
3. How do I create arrays in a HTML <form>?
4. How do I get all the results from a select multiple HTML tag?

1. What encodings/decodings do I need when I pass a value on via a form? And via an URL?

There are several stages for which encoding is important. Assuming that you have a string $data, which contains the string you want to pass on in a non-encoded way, these are the relevant stages:

HTML interpretation. In order to specify a random string, you must include it in double quotes, and htmlspecialchars the the whole value.
URL: A URL consists of several parts. If you want your data to be interpreted as one item, you must encode it with urlencode().

Przykład 50-1. A hidden HTML form element
<?php echo "<input type=hidden value=\"" . htmlspecialchars($data) . "\">\n"; ?>

Notatka: It is wrong to urlencode() $data, because it's the browsers reposability to urlencode() the data. All popular browsers do that correctly. Note that this will happen regardless of the method (i.e., GET or POST). You'll only notice this in case of GET request though, because POST requests are usually hidden.

Przykład 50-2. Data to be edited by the user

<?php
    echo "<textarea name=mydata>\n";
    echo htmlspecialchars($data)."\n";
    echo "</textarea>";
?>

Notatka: The data is shown in the browser as intended, because the browser will interpret the html escaped symbols.
Upon submitting, either via GET or POST, the data will be urlencoded by the browser for transferring, and directly urldecoded by PHP. So in the end, you don't need to do any urlencoding/urldecoding yourself, everything is handeled automagically.

Przykład 50-3. In an URL

<?php
    echo "<a href=\"" . htmlspecialchars("/nexpage.php?stage=23&data=" .
        urlencode($data)) . "\">\n";
?>

Notatka: In fact you are faking a HTML GET request, therefore it's necessary to manually urlencode() the data.

Notatka: You need to htmlspecialchars() the whole URL, because the URL occurs as value of an HTML-attribute. In this case, the browser will first un-htmlspecialchars() the value, and then pass the URL on. PHP will understand the URL correcly, because you urlencoded() the data.
You'll notice that the & in the URL is replaced by &. Although most browsers will recover if you forget this, this isn't always possible. So even if your URL is not dynamic, you need to htmlspecialchars() the URL.

2. I'm trying to use an <input type="image"> tag, but the $foo.x and $foo.y variables aren't available. Where are they?

When submitting a form, it is possible to use an image instead of the standard submit button with a tag like:
<input type="image" src="image.gif" name="foo">
When the user clicks somewhere on the image, the accompanying form will be transmitted to the server with two additional variables: foo.x and foo.y.

Because $foo.x and $foo.y are invalid variable names in PHP, they are automagically converted to $foo_x and $foo_y. That is, the periods are replaced with underscores.

3. How do I create arrays in a HTML <form>?

To get your <form> result sent as an array to your PHP script you name the <input>, <select> or <textarea> elements like this:
<input name="MyArray[]"> <input name="MyArray[]"> <input name="MyArray[]"> <input name="MyArray[]">
Notice the square brackets after the variable name, that's what makes it an array. You can group the elements into different arrays by assigning the same name to different elements:
<input name="MyArray[]"> <input name="MyArray[]"> <input name="MyOtherArray[]"> <input name="MyOtherArray[]">
This produces two arrays, MyArray and MyOtherArray, that gets sent to the PHP script. It's also possible to assign specific keys to your arrays:
<input name="AnotherArray[]"> <input name="AnotherArray[]"> <input name="AnotherArray[email]"> <input name="AnotherArray[phone]">
The AnotherArray array will now contain the keys 0, 1, email and phone.

Notatka: Specifying an arrays key is optional in HTML. If you do not specify the keys, the array gets filled in the order the elements appear in the form. Our first example will contain keys 0, 1, 2 and 3.

4. How do I get all the results from a select multiple HTML tag?

The select multiple tag in an HTML construct allows users to select multiple items from a list. These items are then passed to the action handler for the form. The problem is that they are all passed with the same widget name. ie.
<select name="var" multiple>
Each selected option will arrive at the action handler as:
var=option1 var=option2 var=option3
Each option will overwrite the contents of the previous $var variable. The solution is to use PHP's "array from form element" feature. The following should be used:
<select name="var[]" multiple>
This tells PHP to treat $var as an array and each assignment of a value to var[] adds an item to the array. The first item becomes $var[0], the next $var[1], etc. The count() function can be used to determine how many options were selected, and the sort() function can be used to sort the option array if necessary.

Note that if you are using JavaScript the [] on the element name might cause you problems when you try to refer to the element by name. Use it's numerical form element id instead, or enclose the variable name in single quotes and use that as the index to the elements array, for example:
variable = documents.forms[0].elements['var[]'];

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