Web Programming Step by Step, 2nd Edition

Lecture 8: File I/O; Functions

Reading: 5.4

Except where otherwise noted, the contents of this document are Copyright 2012 Marty Stepp, Jessica Miller, and Victoria Kirst. All rights reserved. Any redistribution, reproduction, transmission, or storage of part or all of the contents in any form is prohibited without the author's expressed written permission.

Functions

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 = "(Wisconsin)";        # 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)

PHP file I/O functions

Reading/writing files

Hello
how r u?

I'm fine

array(
	"Hello\n",     # 0
	"how r u?\n",  # 1
	"\n",          # 2
	"I'm fine\n"   # 3
)

"Hello\n
how r u?\n      # a single
\n              # string
I'm fine\n"

• file function returns lines of a file as an array (\n at end of each)
• file_get_contents returns entire contents of a file as a single string
  • file_put_contents writes a string into a file

The file function

# display lines of file as a bulleted list
$lines = file("todolist.txt");
foreach ($lines as $line) {        # for ($i = 0; $i < count($lines); $i++)
	print $line;
}

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

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

• common idiom: foreach or for loop over lines of file

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) {
	$tokens = explode(" ", $name);
	?>
	<p> author: <?= $tokens[2] ?>, <?= $tokens[0] ?> </p>
	<?php
}

Unpacking an array: list

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

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

list($name, $phone, $ssn) = file("personal.txt");
...
list($area_code, $prefix, $suffix) = explode(" ", $phone);

• the odd list function "unpacks" an array into a set of variables you declare
• when you know a file or line's exact length/format, use file and list to unpack it

Reading directories

• glob can accept a general path with the * wildcard character (more powerful)

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) . "\n";
}

• 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"
• the basename function strips any leading directory from a file path
  • basename("foo/bar/baz.txt") returns "baz.txt"

scandir example

<ul>
	<?php foreach (scandir("taxes/old") as $filename) { ?>
		<li>I found a file: <?= $filename ?></li>
	<?php } ?>
</ul>

• scandir includes current directory (".") and parent ("..") in the array
• don't need basename with scandir; returns file names only without directory

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);

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