Common PHP interview questions (1) (written PHP interview questions)

1. The way PHP Value transfer and reference of

php Pass value ： Within the scope of the function , Change the value of the variable , It will not affect the variable value outside the function .

PHP By reference ： Within the scope of the function , Any change to the value , It's also reflected outside the function , Because it's a memory address .

Advantages and disadvantages ： It takes a lot of time to transfer values , Especially for large strings and objects , It will be a costly operation , Transfer reference , Any operation within a function is equivalent to an operation on a pass variable , High efficiency in transmitting large variables ！

2. Object oriented concept and understanding

（ encapsulation 、 Inherit 、 polymorphic ）

3. Talk about dependency injection

PHP Principle and usage of dependency injection

4. Differences and uses between static classes and static methods

• Static class ： The so-called static class means that it does not need to be instantiated into an object , Classes called directly in a static way , Suitable for making some stateless tools
• Static methods ：

class Test{
    
	const AI = "AI";
	public static $a = "a";
	public static function aAction(){
    
		//TODO
	}
}

Test::aAction();

Methods like this that can be called directly outside without instantiating classes are called static methods .

5. Write the following output

//(1)
$b = 100;
$c = 50;
$a = $b>$c?100:50;
echo $a;	//100

//(2)
$str = “php”;
$$str = “teems”;
$$str .= “coffice”;
echo $php;	//teemscoffice

//(3)
$a = “b”;
$b = “a”;
$ar[$a] = $b;
$ar[$b] = $a;
echo $ar[‘a’];	//b

//(4)
$n = 3.5;
$a = floor($n);
$b = round($n);
echo $a.$b;		//34
echo $a+$b;		//7
// notes ：floor()： Rounding down 
//round() 4 House 5 Rounding in 
//$a=3;$b=4;

6. Please use PHP Write a function to verify whether the email format is correct （ Require regular ）

$gz="/^[0-9a-z]+([-_.][0-9a-z]+)*@([0-9a-z]+\.[a-z]{2,14}(\.[a-z]{2,3})?)$/i";
$email = "[email protected]";
if(preg_match($gz,$email)){
    
    echo " The format is correct ";
}else{
    
    echo " Wrong format ";
}

7. <? echo “Hello CSDN”; ?> No output , What might be the reason . Briefly describe the process of solving this problem

Maybe there is no short tag on the server short_open_tag = Set to Off,php.ini Open the short label control parameters ： short_open_tag = On

8. In a function （ This function doesn't have return sentence ） Inside to deal with global variables , And change his value , There are two ways to achieve （global And quotes &）

// Use Global
$var = 1;
function get_pra(){
    
    global $var;
    $var = "xxx";
    echo $var;
}
echo $var."--";
get_pra();
echo $var;

// Use &
$var1 = 1;
function get_pra1(&$val){
    
    $val +=1;
}
echo $var1."--";
get_pra1($var1);
echo $var1;

9. Write a function , Can traverse all the files and subfolders under a folder .（ Directory operation ）

listDir($dir);

function listDir($dir="./"){
    

    if (is_dir($dir)){
    
        $handle = opendir($dir);
        while (($file = readdir($handle)) !== false){
    
            if ($file == "." || $file == ".."){
    
                continue;
            }
            if (is_dir($sub_dir = realpath($dir.'/'.$file))){
    
                echo " Files in the folder ：".$dir."：".$file.PHP_EOL;
                listDir($sub_dir);
            }else{
    
                echo " The file named ：".$file.PHP_EOL;
            }
        }
        closedir($handle);

    }else{
    
        echo $dir." Not a directory ";
    }

}

10. Can make HTML and PHP Separate the templates used

• Smarty
• Template
• Blade(Laravel Of )

11.PHP The method of realizing infinite classification

Recursion and reference (&)

$array = array(
    array('id' => 1, 'pid' => 0, 'name' => ' Hebei Province '),
    array('id' => 2, 'pid' => 0, 'name' => ' The Beijing municipal '),
    array('id' => 3, 'pid' => 1, 'name' => ' Handan City '),
    array('id' => 4, 'pid' => 2, 'name' => ' Chaoyang District '),
    array('id' => 5, 'pid' => 2, 'name' => ' Tongzhou District '),
    array('id' => 6, 'pid' => 4, 'name' => ' Wangjing '),
    array('id' => 7, 'pid' => 4, 'name' => ' Jiuxianqiao '),
    array('id' => 8, 'pid' => 3, 'name' => ' Yongnian District '),
    array('id' => 9, 'pid' => 1, 'name' => ' Wu'an city '),
);

/** *  Recursive implementation of infinite classification  * @param $array  Classified data  * @param $pid  Father ID * @param $level  Classification level  * @return $list  An array of classes   Just go through it  $level Can be used to traverse indents  */

function getTree($array, $pid =0, $level = 0){
    

    // Declare a static array , Avoid recursive calls , Multiple declarations cause the array to overwrite 
    static $list = [];
    foreach ($array as $key => $value){
    
        // First traversal , Find the node whose parent node is the root node   That is to say pid=0 The node of 
        if ($value['pid'] == $pid){
    
            // The node whose parent node is the root node , The level of 0, That is, the first level 
            $value['level'] = $level;
            // Put the array in list in 
            $list[] = $value;
            // Remove this node from the array , Reduce the consumption of subsequent recursion 
            unset($array[$key]);
            // Start recursion , Find parent ID For this node ID The node of , The level is the original level +1
            getTree($array, $value['id'], $level+1);

        }
    }
    return $list;
}

/* *  Get the recursive data , Traversal generates classification  */
$array = getTree($array);

foreach($array as $value){
    
       echo str_repeat('--', $value['level']), $value['name'].PHP_EOL;
}


/** *  Recursive reference infinite classification  * @param $array  Classified data  * @return array  An array of classes   Just go through it  */
function generateTree($array){
    
    // First step   Structural data 
    $items = array();
    foreach($array as $value){
    
        $items[$value['id']] = $value;
    }
    // Second parts   Traversal data   Generate tree structure 
    $tree = array();
    foreach($items as $key => $value){
    
        if(isset($items[$value['pid']])){
    
            $items[$value['pid']]['son'][] = &$items[$key];
        }else{
    
            $tree[] = &$items[$key];
        }
    }
    return $tree;
}
$array = generateTree($array);
var_dump($array);

12. List several things you know PHP The method of traversing or iterating the array

1. For loop

<?php
for ($i=1; $i<=5; $i++)
{
    
    echo " The number is  " . $i . PHP_EOL;
}
?>

2. Foreach

foreach ($array as $key => $value)
{
    
     To execute code ;
}

3. each
4. list

<?php
$people = array("Peter", "Joe", "Glenn", "Cleveland");
 
reset($people);
 
while (list($key, $val) = each($people))
{
    
    echo "$key => $val<br>";
}
?>

13. Enter the web address in the browser to the page display , What happened during ？

Generally speaking, it is divided into the following processes :

• DNS analysis : Resolve the domain name to IP Address
• TCP Connect ：TCP Three handshakes
• send out HTTP request
• The server processes the request and returns HTTP message
• Browser parse render page
• disconnect ：TCP Four waves

Please refer to the article for details