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    45 个必知必会的 PHP 面试题

    青灯夜游青灯夜游2022-09-20 20:26:51转载438
    本篇文章给大家总结了45 个必知必会的 PHP 面试题 。有一定的参考价值,有需要的朋友可以参考一下,希望对大家有所帮助。

    php入门到就业线上直播课:进入学习

    Q1: == 和 === 之间有什么区别?

    话题: PHP
    困难: ⭐

    这意味着只有当两个操作数具有相同的类型和相同的值时,它才会返回 TRUE。

    1 === 1: true
    1 == 1: true
    1 === "1": false // 1 是一个整数, "1" 是一个字符串
    1 == "1": true // "1" 强制转换为整数,即1
    "foo" === "foo": true // 这两个操作数都是字符串,并且具有相同的值

    ? 源自: stackoverflow.com

    Q2: 如何通过引用传递变量?

    话题: PHP
    困难: ⭐

    为了能够通过引用传递变量,我们在其前面使用 &,如下所示:

    $var1 = &$var2

    ? 源自: guru99.com

    Q3: $GLOBAL 是什么意思?

    话题: PHP
    困难: ⭐

    $GLOBALS 是关联数组,包含对脚本全局范围内当前定义的所有变量的引用。

    ? 源自: guru99.com

    Q4: ini_set () 有什么用处?

    话题: PHP
    困难: ⭐

    PHP 允许用户使用 ini_set () 修改 php.ini 中提到的一些设置。此函数需要两个字符串参数。第一个是要修改的设置的名称,第二个是要分配给它的新值。

    给定的代码行将启用脚本的 display_error 设置 (如果它被禁用)。

    ini_set('display_errors', '1');

    我们需要将上面的语句放在脚本的顶部,以便该设置一直保持启用状态,直到最后。此外,通过 ini_set () 设置的值仅适用于当前脚本。此后,PHP 将开始使用 php.ini 中的原始值。

    ? 源自: github.com/Bootsity

    Q5: 我应该在什么时候使用 require 和 include 呢?

    话题: PHP
    困难: ⭐⭐

    require() 函数与 include() 函数相同,只是它处理错误的方式不同。如果出现错误,include() 函数会生成警告,但脚本会继续执行。require() 函数会产生致命错误,脚本会停止。

    我的建议是 99.9% 的时间里只使用 require_once

    使用 requireinclude 代替意味着您的代码在其他地方不可重用,即您引入的脚本实际上是在执行代码,而不是提供类或某些类功能库。

    ? Source: stackoverflow.com

    Q6: PHP 中的 stdClass 是什么?

    主题: PHP
    难度: ⭐⭐

    stdClass 只是将其他类型强制转换为对象时使用的通用” 空’’类。stdClass 不是 PHP 中对象的基类。这可以很容易地证明:

    class Foo{}
    $foo = new Foo();
    echo ($foo instanceof stdClass)?'Y':'N'; // 输出'N'

    对于匿名对象,动态属性等很有用。

    考虑 StdClass 的一种简单使用场景是替代关联数组。请参见下面的示例,该示例显示 json_decode() 如何允许获取 StdClass 实例或关联数组。
    同样但未在本示例中显示的 SoapClient::__soapCall 返回一个 StdClass 实例。

    //带有StdClass的示例
    $json = '{ "foo": "bar", "number": 42 }';
    $stdInstance = json_decode($json);
    
    echo $stdInstance - > foo.PHP_EOL; //"bar"
    echo $stdInstance - > number.PHP_EOL; //42
    
    //Example with associative array
    $array = json_decode($json, true);
    
    echo $array['foo'].PHP_EOL; //"bar"
    echo $array['number'].PHP_EOL; //42

    ? 源自: stackoverflow.com

    Q7: PHP 中的 die () 和 exit () 函数有什么不同?

    话题: PHP
    困难: ⭐⭐

    没有区别,它们是一样的。 选择 die() 而不是 exit() 的唯一好处可能是你节省了额外键入一个字母的时间.

    ? 源自: stackoverflow.com

    Q8: 它们之间的主要区别是什么

    话题: PHP
    困难: ⭐⭐

    constdefine 的根本区别在于,const 在编译时定义常量,而 define 在运行时定义常量。

    const FOO = 'BAR';
    define('FOO', 'BAR');
    
    // but
    if (...) {
        const FOO = 'BAR';    // 无效
    }
    if (...) {
        define('FOO', 'BAR'); // 有效
    }

    同样在 PHP 5.3 之前,const 命令不能在全局范围内使用。你只能在类中使用它。当你想要设置与该类相关的某种常量选项或设置时,应使用此选项。或者你可能想要创建某种枚举。一个好的 const 用法的例子是摆脱了魔术数字。

    Define 可以用于相同的目的,但只能在全局范围内使用。它应该仅用于影响整个应用程序的全局设置。

    除非你需要任何类型的条件或表达式定义,否则请使用 consts 而不是 define()—— 这仅仅是为了可读性!

    ? 源自: stackoverflow.com

    Q9: isset () 和 array_key_exists () 之间有什么区别?

    话题: PHP
    困难: ⭐⭐

    考虑:

    $a = array('key1' => 'Foo Bar', 'key2' => null);
    
    isset($a['key1']);             // true
    array_key_exists('key1', $a);  // true
    
    isset($a['key2']);             // false
    array_key_exists('key2', $a);  // true

    ? 源自: stackoverflow.com

    Q10: var_dump () 和 print_r () 有什么不同?

    话题: PHP
    困难: ⭐⭐

    考虑:

    $obj = (object) array('qualitypoint', 'technologies', 'India');

    var_dump($obj) 将在屏幕的输出下方显示:

    object(stdClass)#1 (3) {
     [0]=> string(12) "qualitypoint"
     [1]=> string(12) "technologies"
     [2]=> string(5) "India"
    }
    stdClass Object ( 
     [0] => qualitypoint
     [1] => technologies
     [2] => India
    )

    ? 源自: stackoverflow.com

    Q11: 解释不同的 PHP 错误是什么

    话题: PHP
    困难: ⭐⭐

    ? 源自: pangara.com

    Q12: 如何在 PHP 中启用错误报告?

    话题: PHP
    困难: ⭐⭐

    检查 php.ini 中的 “display_errors” 是否等于 “on”,或者在脚本中声明 “ini_set('display_error',1)”。

    然后,在你的代码中包含 “ERROR_REPORTING(E_ALL)”,以便在脚本执行期间显示所有类型的错误消息。
    ? 源自: codementor.io

    Q13: 使用默认参数声明某些函数

    话题: PHP
    困难: ⭐⭐

    思考:

    function showMessage($hello = false){
      echo ($hello) ? 'hello' : 'bye';
    }

    ? 源自: codementor.io

    Q14: PHP 是否支持多重继承?

    话题: PHP
    困难: ⭐⭐

    PHP 只支持单一继承;这意味着使用关键字’extended’只能从一个类扩展一个类。

    ? 源自: guru99.com

    Q15: 在 PHP 中,对象是按值传递还是按引用传递?

    话题: PHP
    困难: ⭐⭐

    在 PHP 中,通过传递的对象。

    ? 源自: guru99.com

    Q16:$a != $b 和 $a !== $b ,之间有什么区别?

    话题: PHP
    困难: ⭐⭐

    != 表示 不等于 (如果 $a 不等于 $b,则为 True), !== 表示 不全等 (如果 $a 与 $b 不相同,则为 True).

    ? 源自: guru99.com

    Q17: 在 PHP 中,什么是 PDO?

    话题: PHP
    困难: ⭐⭐

    PDO 代表 PHP 数据对象。

    它是一组 PHP 扩展,提供核心 PDO 类和数据库、特定驱动程序。它提供了供应商中立、轻量级的数据访问抽象层。因此,无论我们使用哪种数据库,发出查询和获取数据的功能都是相同的。它侧重于数据访问抽象,而不是数据库抽象。

    ? 源自: github.com/Bootsity

    Q18: 说明我们如何在 PHP 中处理异常?

    Topic: PHP
    Difficulty: ⭐⭐

    当程序执行出现异常报错时,后面的代码将不会再执行,这时 PHP 将会尝试匹配第一个 catch 块进行异常的处理,如果没有捕捉到异常程序将会报致命错误并显示”Uncaught Exception”。
    可以在 PHP 中抛出和捕获异常。

    为了处理异常,代码可以被包围在”try” 块中.
    每个 try 必须至少有一个对应的 catch 块 。多个不同的 catch 块可用于捕获不同类的异常。
    在 catch 块中也可以抛出异常(或重新抛出之前的异常)。

    思考:

    try {
        print "this is our try block n";
        throw new Exception();
    } catch (Exception $e) {
        print "something went wrong, caught yah! n";
    } finally {
        print "this part is always executed n";
    }

    ? Source: github.com/Bootsity

    Q19: 区分 echo 和 print ()

    Topic: PHP
    Difficulty: ⭐⭐

    echoprint 基本上是一样的。他们都是用来打印输出数据的。

    区别在于:

    ? Source: github.com/Bootsity

    Q20: require_once 和 require 在什么场景下使用?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    require_once() 作用与 require() 的作用是一样的,都是引用或包含外部的一个 php 文件,require_once() 引入文件时会检查文件是否已包含,如果已包含,不再包含 (require) 它。

    我建议在 99.9% 的时候要使用 require_once

    使用 requireinclude 意味着您的代码不可在其他地方重用,即您要拉入的脚本实际上是在执行代码,而不是提供类或某些函数库。

    ? Source: stackoverflow.com

    Q21: 判断 PHP 数组是否是关联数组

    Topic: PHP
    Difficulty: ⭐⭐⭐

    思考:

    function has_string_keys(array $array) {
      return count(array_filter(array_keys($array), 'is_string')) > 0;
    }

    如果 $array 至少有一个字符串类型的 key ,它将被视为关联数组。

    ? Source: stackoverflow.com

    Q22: 如何将变量和数据从 PHP 传至 Javascript

    Topic: PHP
    Difficulty: ⭐⭐⭐

    这里有几种实现方法:

    思考 get-data.php:

    echo json_encode(42);

    思考 index.html:

    <script>
        function reqListener () {
          console.log(this.responseText);
        }
    
        var oReq = new XMLHttpRequest(); // new 一个请求对象
        oReq.onload = function() {
            // 在这里你可以操作响应数据
            // 真实的数据来自 this.responseText
            alert(this.responseText); // 将提示: 42
        };
        oReq.open("get", "get-data.php", true);
        //                               ^ 不要阻塞的其余部分执行。
        //                                 不要等到请求结束再继续。
        oReq.send();
    </script>
    <div id="dom-target" style="display: none;">
        <?php
            $output = "42"; // 此外, 做一些操作,获得 output.
            echo htmlspecialchars($output); /* 你必须避免特殊字符,不然结果将是无效HTML。 */
        ?>
    </div>
    <script>
        var div = document.getElementById("dom-target");
        var myData = div.textContent;
    </script>
    <script>
        var data = <?php echo json_encode("42", JSON_HEX_TAG); ?>; // Don't forget the extra semicolon!
    </script>

    ? Source: stackoverflow.com

    Q23: 有一个方法可以复制一个 PHP 数组至另一个数组吗?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    PHP 数组通过复制进行赋值,而对象通过引用进行赋值。所有默认情况下,PHP 将复制这个数组。这里有一个 PHP 参考,一目了然:

    $a = array(1,2);
    $b = $a; // $b 是一个不同的数组
    $c = &$a; // $c 是 $a 的引用

    ? Source: stackoverflow.com

    Q24: What will be returned by this code?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    Consider the code:

    $a = new stdClass();
    $a->foo = "bar";
    $b = clone $a;
    var_dump($a === $b);

    What will be echoed to the console?


    Two instances of the same class with equivalent members do NOT match the === operator. So the answer is:

    bool(false)

    ? Source: stackoverflow.com

    Q25: What will be returned by this code? Explain the result.

    Topic: PHP
    Difficulty: ⭐⭐⭐

    Consider the code. What will be returned as a result?

    $something = 0;
    echo ('password123' == $something) ? 'true' : 'false';

    The answer is true. You should never use == for string comparison. Even if you are comparing strings to strings, PHP will implicitly cast them to floats and do a numerical comparison if they appear numerical. === is OK.

    For example

    '1e3' == '1000' // true

    also returns true.

    ? Source: stackoverflow.com

    Q26: What exactly is the the difference between array_map, array_walk and array_filter?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    ? Source: stackoverflow.com

    Q27: Explain the difference between exec() vs system() vs passthru()?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    ? Source: stackoverflow.com

    Q28: How would you create a Singleton class using PHP?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    /**
     * Singleton class
     *
     */
    final class UserFactory {
        /**
         * Call this method to get singleton
         *
         * @return UserFactory
         */
        public static
        function Instance() {
            static $inst = null;
            if ($inst === null) {
                $inst = new UserFactory();
            }
            return $inst;
        }
    
        /**
         * Private ctor so nobody else can instantiate it
         *
         */
        private
        function __construct() {
    
        }
    }

    To use:

    $fact = UserFactory::Instance();
    $fact2 = UserFactory::Instance();

    But:

    $fact = new UserFactory()

    Throws an error.

    ? Source: stackoverflow.com

    Q29: What is the difference between PDO’s query() vs execute()?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    Best practice is to stick with prepared statements and execute for increased security. Aside from the escaping on the client-side that it provides, a prepared statement is compiled on the server-side once, and then can be passed different parameters at each execution.

    ? Source: stackoverflow.com

    Q30: What is use of Null Coalesce Operator?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    Null coalescing operator returns its first operand if it exists and is not NULL. Otherwise it returns its second operand.

    Example:

    $name = $firstName ?? $username ?? $placeholder ?? "Guest";

    ? Source: github.com/Bootsity

    Q31: Differentiate between exception and error

    Topic: PHP
    Difficulty: ⭐⭐⭐

    ? Source: github.com/Bootsity

    Q32: What are the exception class functions?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    There are following functions which can be used from Exception class.

    ? Source: github.com/Bootsity

    Q33: Differentiate between parameterised and non parameterised functions

    Topic: PHP
    Difficulty: ⭐⭐⭐

    ? Source: github.com/Bootsity

    Q34: Explain function call by reference

    Topic: PHP
    Difficulty: ⭐⭐⭐

    In case of call by reference, actual value is modified if it is modified inside the function. In such case, we need to use & symbol with formal arguments. The & represents reference of the variable.

    Example:

    function adder(&$str2) {  
        $str2 .= 'Call By Reference';  
    }
    $str = 'This is ';  
    adder($str);  
    echo $str;

    Output:

    This is Call By Reference

    ? Source: github.com/Bootsity

    Q35: Why do we use extract()?

    Topic: PHP
    Difficulty: ⭐⭐⭐

    The extract() function imports variables into the local symbol table from an array.
    This function uses array keys as variable names and values as variable values. For each element it will create a variable in the current symbol table.
    This function returns the number of variables extracted on success.

    Example:

    $a = "Original";
    $my_array = array("a" => "Cat","b" => "Dog", "c" => "Horse");
    extract($my_array);
    echo "\$a = $a; \$b = $b; \$c = $c";

    Output:

    $a = Cat; $b = Dog; $c = Horse

    ? Source: github.com/Bootsity

    Q36: explain what is a closure in PHP and why does it use the “use” identifier?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    Consider this code:

    public function getTotal($tax)
    {
        $total = 0.00;
    
        $callback =
            function ($quantity, $product) use ($tax, &$total)
            {
                $pricePerItem = constant(__CLASS__ . "::PRICE_" .
                    strtoupper($product));
                $total += ($pricePerItem * $quantity) * ($tax + 1.0);
            };
    
        array_walk($this->products, $callback);
        return round($total, 2);
    }

    Could you explain why use it?


    This is how PHP expresses a closure. Basically what this means is that you are allowing the anonymous function to “capture” local variables (in this case, $tax and a reference to $total) outside of it scope and preserve their values (or in the case of $total the reference to $total itself) as state within the anonymous function itself.

    A closure is a separate namespace, normally, you can not access variables defined outside of this namespace.

    ? Source: stackoverflow.com

    Q37: What exactly are late static bindings in PHP?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    Basically, it boils down to the fact that the self keyword does not follow the same rules of inheritance. self always resolves to the class in which it is used. This means that if you make a method in a parent class and call it from a child class, self will not reference the child as you might expect.

    Late static binding introduces a new use for the static keyword, which addresses this particular shortcoming. When you use static, it represents the class where you first use it, ie. it ‘binds’ to the runtime class.

    Consider:

    class Car {
        public static
        function run() {
            return static::getName();
        }
    
        private static
        function getName() {
            return 'Car';
        }
    }
    
    class Toyota extends Car {
        public static
        function getName() {
            return 'Toyota';
        }
    }
    
    echo Car::run(); // Output: Car
    echo Toyota::run(); // Output: Toyota

    ? Source: stackoverflow.com

    Q38: How to measure execution times of PHP scripts?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    I want to know how many milliseconds a PHP while-loop takes to execute. Could you help me?


    You can use the microtime function for this.

    Consider:

    $start = microtime(true);
    while (...) {
    
    }
    $time_elapsed_secs = microtime(true) - $start;

    ? Source: stackoverflow.com

    Q39: What is the best method to merge two PHP objects?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    //We have this:
    $objectA->a;
    $objectA->b;
    $objectB->c;
    $objectB->d;
    
    //We want the easiest way to get:
    $objectC->a;
    $objectC->b;
    $objectC->c;
    $objectC->d;

    This works:

    $obj_merged = (object) array_merge((array) $obj1, (array) $obj2);

    You may also use array_merge_recursive to have a deep copy behavior.

    One more way to do that is:

    foreach($objectA as $k => $v) $objectB->$k = $v;

    This is faster than the first answer in PHP versions < 7 (estimated 50% faster). But in PHP >= 7 the first answer is something like 400% faster.

    ? Source: stackoverflow.com

    Q40: Compare mysqli or PDO - what are the pros and cons?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    Let’s name some:

    ? Source: stackoverflow.com

    Q41: What is use of Spaceship Operator?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    This <=> operator will offer combined comparison in that it will:

    Consider:

    //Comparing Integers
    echo 1 <= > 1; //outputs 0
    echo 3 <= > 4; //outputs -1
    echo 4 <= > 3; //outputs 1
    
    //String Comparison
    
    echo "x" <= > "x"; // 0
    echo "x" <= > "y"; //-1
    echo "y" <= > "x"; //1

    ? Source: github.com/Bootsity

    Q42: Does PHP have threading?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    Standard php does not provide any multithreading but there is an (experimental) extension that actually does - pthreads. The next best thing would be to simply have one script execute another via CLI, but that’s a bit rudimentary. Depending on what you are trying to do and how complex it is, this may or may not be an option.

    ? Source: github.com/Bootsity

    Q43: Is PHP single or multi threaded?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐

    PHP is not single threaded by nature. It is, however, the case that the most common installation of PHP on unix systems is a single threaded setup, as is the most common Apache installation, and nginx doesn’t have a thread based architecture whatever. In the most common Windows setup and some more advanced unix setups, PHP can and does operate multiple interpreter threads in one process.

    PHP as an interpreter had support for multi-threading since the year 2000.

    ? Source: github.com/Bootsity

    Q44: Provide some ways to mimic multiple constructors in PHP

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐⭐

    It’s known you can’t put two __construct functions with unique argument signatures in a PHP class but I’d like to do something like this:

    class Student 
    {
       protected $id;
       protected $name;
       // etc.
    
       public function __construct($id){
           $this->id = $id;
          // other members are still uninitialised
       }
    
       public function __construct($row_from_database){
           $this->id = $row_from_database->id;
           $this->name = $row_from_database->name;
           // etc.
       }
    }

    What is the best way to achieve this in PHP?


    I’d probably do something like this:

    class Student
    {
        public function __construct() {
            // allocate your stuff
        }
    
        public static function withID( $id ) {
            $instance = new self();
            $instance->loadByID( $id );
            return $instance;
        }
    
        public static function withRow( array $row ) {
            $instance = new self();
            $instance->fill( $row );
            return $instance;
        }
    
        protected function loadByID( $id ) {
            // do query
            $row = my_awesome_db_access_stuff( $id );
            $this->fill( $row );
        }
    
        protected function fill( array $row ) {
            // fill all properties from array
        }
    }

    Then if i want a Student where i know the ID:

    $student = Student::withID( $id );

    Technically you’re not building multiple constructors, just static helper methods, but you get to avoid a lot of spaghetti code in the constructor this way.

    Another way is to use the mix of factory and fluent style:

    class Student
    {
        protected $firstName;
        protected $lastName;
        // etc.
    
        /**
         * Constructor
         */
        public function __construct() {
            // allocate your stuff
        }
    
        /**
         * Static constructor / factory
         */
        public static function create() {
            $instance = new self();
            return $instance;
        }
    
        /**
         * FirstName setter - fluent style
         */
        public function setFirstName( $firstName) {
            $this->firstName = $firstName;
            return $this;
        }
    
        /**
         * LastName setter - fluent style
         */
        public function setLastName( $lastName) {
            $this->lastName = $lastName;
            return $this;
        }
    }
    
    // create instance
    $student= Student::create()->setFirstName("John")->setLastName("Doe");

    ? Source: stackoverflow.com

    Q45: How could we implement method overloading in PHP?

    Topic: PHP
    Difficulty: ⭐⭐⭐⭐⭐

    You cannot overload PHP functions. Function signatures are based only on their names and do not include argument lists, so you cannot have two functions with the same name.

    You can, however, declare a variadic function that takes in a variable number of arguments. You would use func_num_args() and func_get_arg() to get the arguments passed, and use them normally.

    Consider:

    function myFunc() {
        for ($i = 0; $i < func_num_args(); $i++) {
            printf("Argument %d: %s\n", $i, func_get_arg($i));
        }
    }
    
    /*
    Argument 0: a
    Argument 1: 2
    Argument 2: 3.5
    */
    myFunc('a', 2, 3.5);

    ? Source: github.com/Bootsity

    为了处理异常,代码可能被包围在一个 try 块中。

    每个 try 必须至少有一个提示。

    原文地址:https://dev.to/fullstackcafe/45-important-php-interview-questions-that-may-land-you-a-job-1794

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