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PHP Certification -- Feb 2023

Homework

For Thu 23 Feb 2023

  • Quiz questions for Topic #8 (Database)
  • Quiz questions for Topic #9 (Security)
  • Quiz questions for Topic #10 (Web)
  • Quiz questions for Topic #11 (Error)
  • Final Mock Exam

For Tue 21 Feb 2023

  • Quiz questions for Topic #6 (Functions)
  • Quiz questions for Topic #7 (OOP)
  • Mock Exam #1
  • Mock Exam #2

For Thu 16 Feb 2023

  • Quiz questions for Topic #4 (Arrays)
  • Quiz questions for Topic #5 (I/O)

For Tue 14 Feb 2023

  • Quiz questions for Topic #2 (Data Formats and Types)
  • Quiz questions for Topic #3 (Strings and Patterns)

Class Notes

<?php
namespace X {
    class Test {}
}

namespace Y {
    class Test {}
}

namespace Z {
    // must use alias, otherwise PHP doesn't know which "Test" you're referring to
    use X\Test as XT;
    use Y\Test as YT;
    $test = new XT();
}
  • Type coercion / type juggling
    • Study this example:
<?php
$a = 123;
$b = 456;
$c = '789';
// in the case combined operations, the last one wins
$e = $a + $b . $c;
var_dump($e);   // string(579789)
$e = $a . $b + $c;
var_dump($e);   // int(124245)
// the data type of $b is changed because of the string operators "."
$b = $a . '+' . $b;
var_dump($b);
// the data type of $c is "juggled" temporarily to int to satisfy the operation
$d = $a + $c;
var_dump($c);
  • Example of left/right shift
<?php
$three = 0b00000011; // 3
// 3 << 5
$final = 0b01100000; // 96
// 96 >> 5
$final = 0b00000011; // 4
// same thing but using 7
$three = 0b00000111; // 7
// 3 << 5
$final = 0b11100000; // 224
// 224 >> 6
$final = 0b00000011; // 3

Docker Container Setup

  • Download the ZIP file via Zoom
  • Unzip into a new folder /path/to/zip
  • Follow the setup instructions in /path/to/zip/README.md

Q & A

What's the difference between define() and const for constants:

<?php
namespace x {
    define('TEST1', 'xyz');
    const TEST2 = 'abc';
}

namespace y {

    function test()
    {
        return TEST1 . TEST2;
    }

    echo test();
    // output: xyzTEST2
}

Namespaces:

  • Cannot have keywords in the namespace in PHP 7.1
namespace Test\List\Whatever;

use ArrayObject;

$obj = new ArrayObject([1,2,3,4,5]);
var_dump($obj);
// PHP Parse error:  syntax error, unexpected 'List' (T_LIST), expecting identifier (T_STRING) in /srv/code/test.php on line 2

IMPORTANT: when assigning objects, it's automatically by reference (even without the &)

<?php
$obj = new stdClass();
$obj->name = 'TEST';
$abc = $obj;
$abc->name = 'Whatever';
echo $obj->name;
echo PHP_EOL;
// Output: "Whatever"

What is considered "empty"?

<?php
namespace abc {
        define('WHATEVER', 'Whatever', TRUE);
        const ANYTHING = 'Anything';
}

namespace xyz {
        echo WHATEVER;
        echo ANYTHING;
}

Bitwise Operators

Tutorial oriented towards the exam:

<?php
echo "Logical AND\n";
printf("%04b\n", 0b00 & 0b00);  // 0
printf("%04b\n", 0b00 & 0b01);  // 0
printf("%04b\n", 0b01 & 0b00);  // 0
printf("%04b\n", 0b01 & 0b01);  // 1

echo "Logical OR\n";
printf("%04b\n", 0b00 | 0b00);  // 0
printf("%04b\n", 0b00 | 0b01);  // 1
printf("%04b\n", 0b01 | 0b00);  // 1
printf("%04b\n", 0b01 | 0b01);  // 1

echo "Logical XOR\n";
printf("%04b\n", 0b00 ^ 0b00);  // 0
printf("%04b\n", 0b00 ^ 0b01);  // 1
printf("%04b\n", 0b01 ^ 0b00);  // 1
printf("%04b\n", 0b01 ^ 0b01);  // 0

Examples of the three ops:

<?php
$a = 0b11111111;
$b = 0b11011101;

printf("%08b", $a & $b); // 1101 1101
printf("%08b", $a | $b); // 1111 1111
printf("%08b", $a ^ $b); // 0010 0010

Left/right shift illustration:

<?php
echo 16 << 3;
echo "\n";
echo 0b10000000;
echo "\n";

echo 16 >> 3;
echo "\n";
echo 0b00000010;
echo "\n";

echo 15 >> 3;
echo "\n";
echo 0b00000001;
echo "\n";

Nested Ternary Construct

$a = 30;
$b = 20;
echo ($a < $b) ? 'Less' : (($a == $b) ? 'Equal' : 'Greater');
// output: "Greater"

Null coalesce operator example

$token = $_GET['token'] ?? $_POST['token'] ?? $_COOKIE['token'] ?? 'DEFAULT';

Yet another example

<?php
// example of null coalesce operator
// first expression is the 1st CLI arg
// if that's not present, looks to the URL or post
$action = $argv[1] ?? $_GET['action'] ?? $_POST['action'] ?? 'nothing';

php.ini file settings:

Garbage Collection

Data Formats

Read up on SimpleXMLElement

<?php
$xml = <<<EOT
<topics>
    <topic id="1">XML</topic>
    <topic id="2">Web Services</topic>
    <topic id="3">Whatever</topic>
    <info>
        <name>Doug</name>
        <name>Hudo</name>
    </info>
</topics>
EOT;

$simple = new SimpleXMLElement($xml);
echo $simple->info->name;       // Doug
echo $simple->info->name[1];    // Hudo
echo $simple->topic[2];         // Whatever
echo $simple->topic[2]['id'];   // 3

<?php
// for relative formats see:
// https://www.php.net/manual/en/datetime.formats.relative.php
$date[] = new DateTime('third thursday of next month');
$date[] = new DateTime('now', new DateTimeZone('CET'));
$date[] = new DateTime('@' . time());
$date[] = (new DateTime())->add(new DateInterval('P3D'));
var_dump($date);

Strings

  • Be very careful with strpos() and stripos()
<?php
$str = 'The quick brown fox jumped over the fence';
echo '"The" was ';
echo (stripos($str, 'The')) ? 'found' : 'not found';
echo ' in the string ' . $str;
echo PHP_EOL;

// actual output:
// "The" was not found in the string The quick brown fox jumped over the fence
  • Study substr() with negative args
<?php
$a = 'test.php';
//   test.               php
$b = substr($a, 0, -3) . substr($a, -3);
echo ($a === $b) ? 'T' : 'F';

// ouput: "T"
  • Study the docs on sprintf() to get format codes for that family of functions
  • Example using negative offsets:
<?php
$dir = '/home/doug/some/directory/';
if (substr($dir, 0, 1) === '/') echo 'Leading slash' . PHP_EOL;
if (substr($dir, -1) === '/') echo 'Trailing slash' . PHP_EOL;
if ($dir[-1] === '/') echo 'Trailing slash' . PHP_EOL;

<?php
$text = 'Doug Bierer';
$patt = '/(.*)\s(.*)/';
echo preg_replace($patt, '$2, $1', $text);
  • preg_replace() and preg_match() example using sub-patterns:
<?php
$string = 'April 15, 2003';
$pattern = '/(\w+) (\d+), (\d+)/i';
$replacement = '$2 $1 $3';
echo preg_replace($pattern, $replacement, $string);

preg_match($pattern, $string, $matches);
var_dump($matches);
  • Same thing, but going from European date format to American
<?php
$str = '5 April 2022';
$pat = '/^(\d+?) (\w+?) (\d{4})$/';
$rep = '$2 $1, $3';
echo preg_replace($pat, $rep, $str);
echo PHP_EOL;

Greediness Example:

<?php
$str = '<p>Para 1</p><p>Para 2</p><p>Para 3</p>';
// $pat = '!<p>.*</p>!';    // returns the entire string
$pat = '!<p>.*?</p>!';  // returns "<p>Para 1</p>"
preg_match($pat, $str, $matches);
var_dump($matches);
echo PHP_EOL;

General regex coding examples:

Arrays

For iterating through an array beginning-to-end don't forget about these functions:

  • array_walk()
  • array_walk_recursive()
  • array_map() Also: please don't forget the array navigation functions:
  • reset(): sets pointer to top
  • end() : sets pointer to end
  • prev() : advances array pointer
  • next() : un-advances array pointer
  • key() : returns index value at array pointer
  • current() : returns value of element at array pointer

I/O

Streams

  • Don't have to study all functions, just certain of the more common ones
  • https://www.php.net/streams
    • stream_context_create()
    • stream_wrapper_register()
    • stream_filter_register()
    • stream_filter_append()
    • stream_socket_client() In addition to the informational file functions mentioned, you also have:
  • fileatime()
  • filemtime()
  • filectime() etc.

Functions

<?php
$label = 'Result: ';
$add = function ($a, $b) use ($label) {
    return $label . ($a + $b);
};

$sub = function ($a, $b) use ($label) {
    return $label . ($a - $b);
};

echo $add(6, 3) . PHP_EOL . $sub(6, 3);
// Result: 9
// Result: 3
  • Alternative example of bindTo()
<?php
class Airplane {
    public $type;
    function __construct(string $type) {
        $this->type = $type;
    }
    function getClosure() {
        return function() {
            return $this->type;
        };
    }
}
class X {
    public $type = 'X';
}

$airplane1 = new Airplane('Airliner');
$closure1 = $airplane1->getClosure();
echo $closure1(). PHP_EOL;
$closure2 = $closure1->bindTo(new X());
echo $closure2();

OOP

<?php
interface SetGet {
    public function set(string $name, callable $service);
    public function get(string $name) : callable;
}
abstract class Container implements SetGet {
    protected $services = [];
}
class ServiceContainer extends Container {
    /*
    public function set(string $name, callable $value) {
        $this->services[$name] = $value;
    }
    */
    public function get(string $name) : callable {
        return $this->services[$name];
    }
}
$service = function () { return (new DateTime('now'))->format('l, d M Y'); };
$container = new ServiceContainer();
$container->set('today', $service);
echo $container->get('today')();

<?php
class Test
{
        public $a = 0;
        public $b = 0;
    public $c = 'Test';
    public $d = [];
    public $e = '';
        public function __construct(int $a, float $b, string $c, array $d)
        {
                $this->a = $a;
                $this->b = $b;
                $this->c = $c;
                $this->d = $d;
                $this->e = md5(rand(1111,9999));
        }
        public function __sleep()
        {
                return ['a','b','c','d'];
        }
        public function __wakeup()
        {
                $this->e = md5(rand(1111,9999));
        }
}
$test = new Test(222, 3.456, 'TEST', [1,2,3]);
var_dump($test);
$str = serialize($test);
echo $str . PHP_EOL;

$obj = unserialize($str);
var_dump($obj);
  • Type hints
    • If declare(strict_types=1) is not set, the type hint does a "soft" type cast
<?php
function test (int $a, int $b)
{
    return $a + $b;
}

echo test(2, 2);
echo PHP_EOL;
echo test('2', '2');
echo PHP_EOL;
echo test(2.666, 2.777);
echo PHP_EOL;
echo test('A', 'B');
echo PHP_EOL;
// actual output:
/*
4
4
4
PHP Fatal error:  Uncaught TypeError: Argument 1 passed to test() must be of the type integer, string given, called in /srv/code/test.php on line 13 and defined in /srv/code/test.php:2
*/

Database Topic

Fetch Modes:

Security Topic

Questions are drawn from here:

Web Features

Make sure you're up on the php.ini settings pertaining to web features URL: https://www.php.net/manual/en/ini.list.php

  • variables_order
  • request_order
  • memory_limit
  • post_max_size
  • upload_max_filesize
  • file_uploads
  • max_file_uploads

Error Handling

Example of aggregated Catch block:

try {
    $pdo = new PDO($params);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException | Exception $e) {
    error_log('Database error: ' . date('Y-m-d H:i:s'));
} catch (Throwable $e) {
    error_log('Any and all errors or exceptions: ' . date('Y-m-d H:i:s'));
} finally {
    echo 'Database connection ';
    echo ($pdo) ? 'succeeded' : 'failed';
}

Example of making object callable:

<?php
$sum = new class () {
    public $num = 0;
    public function __invoke($val) {
        $this->num += $val;
    }
};

$a = [1, 2, 3, 4, 5, 6, 7, 8];
array_walk($a, $sum);
echo 'Sum of Digits: ' . $sum->num;
// output: 36

See: https://github.com/dbierer/classic_php_examples/blob/master/oop/callable_examples.php

Error Handling

<?php
$err = [
    E_NOTICE,
    E_PARSE,
    E_WARNING,
    E_ERROR,
    E_STRICT,
    E_DEPRECATED,
    E_ALL
];
foreach ($err as $x)
    printf("%016b\n", $x);

Resources

Q & A

Q & A

  • Q: Why doesn't this work?
<?php
class CParent
{
    function visit(CParent $p) { /*...*/ }
}
class Child extends CParent
{
    function visit($p) { echo 'TEST'; }
}
  • A: It actually does work, but in PHP 7 a Warning is issued.
  • A: Here's a rewritten example that more effectively proves the point:
<?php
ini_set('display_errors', 0);
echo PHP_VERSION . PHP_EOL;

class CParent {
    function visit(CParent $p) { /*...*/ }
}

echo 'A: ';
try {
    $a = new class extends CParent {
        function visit(CParent $p, $x) { echo 'TEST'; }
    };
    echo 'Works OK';
} catch (Throwable $t) {
    echo get_class($t);
}
echo "\n";

echo 'B: ';
try {
    $a = new class extends CParent {
        function visit($p) { echo 'TEST'; }
    };
    echo 'Works OK';
} catch (Throwable $t) {
    echo get_class($t);
}
echo "\n";

echo 'C: ';
try {
    $a = new class extends CParent {
        function visit(ChildC $p) { echo 'TEST'; }
    };
    echo 'Works OK';
} catch (Throwable $t) {
    echo get_class($t);
}
echo "\n";

echo 'D: ';
try {
    $a = new class extends CParent {
        protected function visit($p) { echo 'TEST'; }
    };
    echo 'Works OK';
} catch (Throwable $t) {
    echo get_class($t);
}
echo "\n";

// Actual output:
/*
7.1.33
A: PHP Warning:  Declaration of class@anonymous::visit(CParent $p, $x) should be compatible with CParent::visit(CParent $p) in /srv/code/exam-3-21.php on line 11
PHP Stack trace:
PHP   1. {main}() /srv/code/exam-3-21.php:0
Works OK
B: PHP Warning:  Declaration of class@anonymous::visit($p) should be compatible with CParent::visit(CParent $p) in /srv/code/exam-3-21.php on line 22
PHP Stack trace:
PHP   1. {main}() /srv/code/exam-3-21.php:0
Works OK
C: PHP Warning:  Declaration of class@anonymous::visit(ChildC $p) should be compatible with CParent::visit(CParent $p) in /srv/code/exam-3-21.php on line 33
PHP Stack trace:
PHP   1. {main}() /srv/code/exam-3-21.php:0
Works OK
D: PHP Fatal error:  Access level to class@anonymous::visit() must be public (as in class CParent) in /srv/code/exam-3-21.php on line 44
PHP Stack trace:
PHP   1. {main}() /srv/code/exam-3-21.php:0
*/

Change Request

  • http://localhost:8884/#/12/8
    • PDOException | Exception doesn't make sense!
  • Mock Final Question 21
    • When running code, none of the answers work!