Web Programming Step by Step

Lecture 8
PHP File I/O and Query Parameters

Reading: 5.4 - 5.5

Except where otherwise noted, the contents of this presentation are Copyright 2009 Marty Stepp and Jessica Miller.

Functions (5.4.1)

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

function quadratic($a, $b, $c) {
	return -$b + sqrt($b * $b - 4 * $a * $c) / (2 * $a);
}

• parameter types and return types are not written
• a function with no return statements implicitly returns NULL

Calling functions

name(expression, ..., expression);

$x = -2;
$a = 3;
$root = quadratic(1, $x, $a - 2);

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

Default parameter values

function name(parameterName, ..., parameterName) {
	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)

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
• variables not declared in a function are global
• if a function wants to use a global variable, it must have a global statement

Query strings and parameters (6.1.1)

URL?name=value&name=value...

http://www.google.com/search?q=Obama
http://example.com/student_login.php?username=stepp&id=1234567

• query string: a set of parameters passed from a browser to a web server
  • often passed by placing name/value pairs at the end of a URL
  • above, parameter username has value stepp, and sid has value 1234567
• PHP code on the server can examine and utilize the value of parameters
• a way for PHP code to produce different output based on values passed by the user

Query parameters: $_REQUEST (6.4.2)

$user_name = $_REQUEST["username"];
$id_number = (int) $_REQUEST["id"];
$eats_meat = FALSE;
if (isset($_REQUEST["meat"])) {
	$eats_meat = TRUE;
}

• $_REQUEST["parameter name"] returns a parameter's value as a string
• test whether a given parameter was passed with isset

PHP file I/O functions (5.4.5)

Reading/writing files

Hello
how are
you?

I'm fine

array(
	"Hello\n",    # 0
	"how are\n",  # 1
	"you?\n",     # 2
	"\n",         # 3
	"I'm fine\n"  # 4
)

"Hello\n
how are\n
you?\n
\n
I'm fine\n"

• file returns lines of a file as an array
• file_get_contents returns entire contents of a file as a string

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'll get a warning
• file_put_contents writes a string into a file, replacing any prior contents

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);

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
• appends (adds to the end) rather than replacing previous contents

The file function

# display lines of file as a bulleted list
$lines = file("todolist.txt");
foreach ($lines as $line) {
	?>
	<li> <?= $line ?> </li>
	<?php
}

• file returns the lines of a file as an array of strings
  • each string ends with \n
  • to strip the \n off each line, use optional second parameter:

    $lines = file("todolist.txt", FILE_IGNORE_NEW_LINES);
    

• common idiom: foreach loop over lines of file

Unpacking an array: list

list($var1, ..., $varN) = array;

$values = array("stepp", "17", "m", "94");
...
list($username, $age, $gender, $iq) = $values;

• the list function accepts a comma-separated list of variable names as parameters
• can be assigned from an array (or the result of a function that returns an array)
• use this to quickly "unpack" an array's contents into several variables
  • a convenience, so you can refer to $username instead of $values[0], etc.

Fixed-length files, file and list

Marty Stepp
(206) 685-2181
570-86-7326

list($name, $phone, $ssn) = file("personal.txt");
...

• when you know a file's exact length/format, you can use file and list to quickly examine it
• reads the file into an array of lines and unpacks the lines into variables

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

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
}

Reading directories

• glob can filter by accepting wildcard paths with the * character

glob example

# reverse all poems in the poetry directory
$poems = glob("poetry/poem*.dat");
foreach ($poems as $poemfile) {
	$text = file_get_contents($poemfile);
	file_put_contents($poemfile, strrev($text));
	print "I just reversed " . basename($poemfile);
}

• glob can match a "wildcard" path with the * character
  • glob("foo/bar/*.doc") returns all .doc files in the foo/bar subdirectory
  • glob("food*") returns all files whose names begin with "food"
  • glob("lecture*/slides*.ppt") examines all directories whose names begin with lecture and grabs all files whose names begin with "slides" and end with ".ppt"
• the basename function strips any leading directory from a file path
  • basename("foo/bar/baz.txt") returns "baz.txt"

scandir example

<ul>
	<?php
	$folder = "taxes/old";
	foreach (scandir($folder) as $filename) {
		?>
		<li> <?= $filename ?> </li>
		<?php
	}
	?>
</ul>

• annoyingly, the current directory (".") and parent directory ("..") are included in the array
• don't need basename with scandir because it returns the file's names only