Web Programming Step by Step

Lecture 8
Embedded PHP

Reading: 5.3 - 5.5

Functions; More File I/O

5.1: Server-Side Basics
5.2: PHP Basic Syntax
5.3: Embedded PHP
5.4: Advanced PHP Syntax

Functions (5.4.1)

function name(parameterName, ..., parameterName) {
	statements;
}

function bmi($weight, $height) {
	$result = 703 * $weight / $height / $height;
	return $result;
}

parameter types and return types are not written
a function with no return statements is implicitly "void"
can be declared in any PHP block, at start/end/middle of code

Calling functions

name(expression, ..., expression);

$w = 163;  # pounds
$h = 70;   # inches
$my_bmi = bmi($w, $h);

if the wrong number of parameters are passed, it's an error

Variable scope: global and local vars

$school = "UW";                   # global
...

function downgrade() {
	global $school;
	$suffix = "Tacoma";             # local

	$school = "$school $suffix";
	print "$school\n";
}

variables declared in a function are local to that function; others are global
if a function wants to use a global variable, it must have a global statement
- but don't abuse this; mostly you should use parameters

Default parameter values

function name(parameterName = value, ..., parameterName = value) {
	statements;
}

function print_separated($str, $separator = ", ") {
	if (strlen($str) > 0) {
		print $str[0];
		for ($i = 1; $i < strlen($str); $i++) {
			print $separator . $str[$i];
		}
	}
}

print_separated("hello");        # h, e, l, l, o
print_separated("hello", "-");   # h-e-l-l-o

if no value is passed, the default will be used (defaults must come last)

Reading/writing an entire file

# reverse a file
$text = file_get_contents("poem.txt");
$text = strrev($text);
file_put_contents("poem.txt", $text);

file_get_contents returns entire contents of a file as a string
- if the file doesn't exist, you will get a warning and an empty return string
file_put_contents writes a string into a file, replacing its old contents
- if the file doesn't exist, it will be created

Appending to a file

# add a line to a file
$new_text = "P.S. ILY, GTG TTYL!~";
file_put_contents("poem.txt", $new_text, FILE_APPEND);

old contents	new contents
Roses are red, Violets are blue. All my base, Are belong to you.	Roses are red, Violets are blue. All my base, Are belong to you. P.S. ILY, GTG TTYL!~

file_put_contents can be called with an optional third parameter to append (add to the end) rather than overwrite

Splitting/joining strings

$array = explode(delimiter, string);
$string = implode(delimiter, array);

$s  = "CSE 190 M";
$a  = explode(" ", $s);     # ("CSE", "190", "M")
$s2 = implode("...", $a);   # "CSE...190...M"

explode and implode convert between strings and arrays
for more complex string splitting, you can use regular expressions (later)

Example with `explode`

contents of input file names.txt

Martin D Stepp
Jessica K Miller
Victoria R Kirst

foreach (file("names.txt") as $name) {
	list($first, $mid, $last) = explode(" ", $name);
	?>
	<p> author: <?= $last ?>, <?= $first ?> </p>
	<?php
}

author: Stepp, Marty

author: Miller, Jessica

author: Kirst, Victoria

The `htmlspecialchars` function

htmlspecialchars returns an HTML-escaped version of a string

text that comes from files / user input might contain <, >, &, etc.
we could manually write code to strip out these characters
better idea: allow them, but escape them

$text = "<p>hi 2 u & me</p>";
$text = htmlspecialchars($text);   # "&lt;p&gt;hi 2 u &amp; me&lt;/p&gt;"

5.3: Embedded PHP

5.1: Server-Side Basics
5.2: PHP Basic Syntax
5.3: Embedded PHP
5.4: Advanced PHP Syntax

Printing HTML tags in PHP = bad style

<?php
print "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.1//EN\"\n";
print " \"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd\">\n";
print "<html xmlns=\"http://www.w3.org/1999/xhtml\">\n";
print "  <head>\n";
print "    <title>Geneva's web page</title>\n";
...
for ($i = 1; $i <= 10; $i++) {
	print "<p> I can count to $i! </p>\n";
}
?>

printing HTML tags with print statements is bad style and error-prone:
- must quote the HTML and escape special characters, e.g. \"
but without print, how do we insert dynamic content into the page?

PHP expression blocks (5.3.2)

<?= expression ?>

<h2> The answer is <?= 6 * 7 ?> </h2>

The answer is 42

PHP expression block: evaluates and embeds an expression's value into HTML
<?= expr ?> is equivalent to <?php print expr; ?>

Expression block example

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
 "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
	<head><title>CSE 190 M: Embedded PHP</title></head>	
	<body>
		<?php
		for ($i = 99; $i >= 1; $i--) {
			?>
			<p> <?= $i ?> bottles of beer on the wall, <br />
				  <?= $i ?> bottles of beer. <br />
				  Take one down, pass it around, <br />
				  <?= $i - 1 ?> bottles of beer on the wall. </p>
			<?php
		}
		?>
	</body>
</html>

Common errors: unclosed braces, missing = sign

	<body>
		<p>Watch how high I can count:
			<?php
			for ($i = 1; $i <= 10; $i++) {
				?>
				<? $i ?>
		</p>
	</body>
</html>

</body> and </html> above are inside the for loop, which is never closed
if you forget to close your braces, you'll see an error about 'unexpected $end'
if you forget = in <?=, the expression does not produce any output

Complex expression blocks

	<body>
		<?php
		for ($i = 1; $i <= 3; $i++) {
			?>
			<h<?= $i ?>>This is a level <?= $i ?> heading.</h<?= $i ?>>
			<?php
		}
		?>
	</body>

This is a level 1 heading.

This is a level 2 heading.

This is a level 3 heading.

expression blocks can even go inside HTML tags and attributes

Web Programming Step by Step, Lecture 8

Embedded PHP

Web Programming Step by Step

Lecture 8 Embedded PHP

Reading: 5.3 - 5.5

Functions; More File I/O

Functions (5.4.1)

Calling functions

Variable scope: global and local vars

Default parameter values

Reading/writing an entire file

Appending to a file

Splitting/joining strings

Example with explode

The htmlspecialchars function

5.3: Embedded PHP

Printing HTML tags in PHP = bad style

PHP expression blocks (5.3.2)

The answer is 42

Expression block example

Common errors: unclosed braces, missing = sign

Complex expression blocks

This is a level 1 heading.

This is a level 2 heading.

This is a level 3 heading.

Lecture 8
Embedded PHP

Example with `explode`

The `htmlspecialchars` function