PHP面試題問(wèn)答題有哪些

1 === 1: true
1 == 1: true
1 === "1": false // 1 是一個(gè)整數(shù), "1" 是一個(gè)字符串
1 == "1": true // "1" 強(qiáng)制轉(zhuǎn)換為整數(shù)，即1
"foo" === "foo": true // 這兩個(gè)操作數(shù)都是字符串，并且具有相同的值

$var1 = &$var2

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

//帶有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

const FOO = 'BAR';
define('FOO', 'BAR');

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

$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

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

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

stdClass Object ( 
 [0] => qualitypoint
 [1] => technologies
 [2] => India
)

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

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";
}

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

echo json_encode(42);

• 直接在 JavaScript 代碼中 echo 數(shù)據(jù)。

? Source:stackoverflow.com

Q23: 有一個(gè)方法可以復(fù)制一個(gè) PHP 數(shù)組至另一個(gè)數(shù)組嗎？

Topic: PHP
Difficulty: ???

PHP 數(shù)組通過(guò)復(fù)制進(jìn)行賦值，而對(duì)象通過(guò)引用進(jìn)行賦值。所有默認(rèn)情況下，PHP 將復(fù)制這個(gè)數(shù)組。這里有一個(gè) PHP 參考，一目了然：

$a = array(1,2);
$b = $a; // $b 是一個(gè)不同的數(shù)組
$c = &$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: ???

• array_walk takes an array and a function F and modifies it by replacing every element x with F(x).

• array_map does the exact same thing exceptthat instead of modifying in-place it will return a new array with the transformed elements.

• array_filter with function F, instead of transforming the elements, will remove any elements for which F(x) is not true

? Source:stackoverflow.com

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

Topic: PHP
Difficulty: ???

• exec() is for calling a system command, and perhaps dealing with the output yourself.

• system() is for executing a system command and immediately displaying the output - presumably text.

• passthru() is for executing a system command which you wish the raw return from - presumably something binary.

? 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: ???

• query runs a standard SQL statement and requires you to properly escape all data to avoid SQL Injections and other issues.

• execute runs a prepared statement which allows you to bind parameters to avoid the need to escape or quote the parameters. execute will also perform better if you are repeating a query multiple times.

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: ???

• Recovering from Error is not possible. The only solution to errors is to terminate the execution. Where as you can recover from Exception by using either try-catch blocks or throwing exception back to caller.

• You will not be able to handle the Errors using try-catch blocks. Even if you handle them using try-catch blocks, your application will not recover if they happen. On the other hand, Exceptions can be handled using try-catch blocks and can make program flow normal if they happen.

• Exceptions are related to application where as Errors are related to environment in which application is running.

? 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.

• getMessage() ? message of exception

• getCode() ? code of exception

• getFile() ? source filename

• getLine() ? source line

• getTrace() ? n array of the backtrace()

• getTraceAsString() ? formated string of trace

• Exception::__toString gives the string representation of the exception.

? Source:github.com/Bootsity

Q33: Differentiate between parameterised and non parameterised functions

Topic: PHP
Difficulty: ???

• Non parameterised functionsdon’t take any parameter at the time of calling.

• Parameterised functionstake one or more arguments while calling. These are used at run time of the program when output depends on dynamic values given at run time There are two ways to access the parameterised function:

• call by value: (here we pass the value directly )

• call by reference: (here we pass the address location where the value is stored)

? 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.

• use allows you to access (use) the succeeding variables inside the closure.

• use is early binding. That means the variable values are COPIED upon DEFINING the closure. So modifying $tax inside the closure has no external effect, unless it is a pointer, like an object is.

• You can pass in variables as pointers like in case of &$total. This way, modifying the value of $total DOES HAVE an external effect, the original variable’s value changes.

? 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:

• PDO is the standard, it’s what most developers will expect to use.

• Moving an application from one database to another isn’t very common, but sooner or later you may find yourself working on another project using a different RDBMS. If you’re at home with PDO then there will at least be one thing less to learn at that point.

• A really nice thing with PDO is you can fetch the data, injecting it automatically in an object.

• PDO has some features that help agains SQL injection

• In sense of speed of execution MySQLi wins, but unless you have a good wrapper using MySQLi, its functions dealing with prepared statements are awful. inserts - almost equal, selects - mysqli is2.5% faster for non-prepared statements/6.7% faster for prepared statements.

? Source:stackoverflow.com

Q41: What is use of Spaceship Operator?

Topic: PHP
Difficulty: ????

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

• Return 0 if values on either side are equal

• Return 1 if value on the left is greater

• Return -1 if the value on the right is greater

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 functionthat 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

為了處理異常，代碼可能被包圍在一個(gè) try 塊中。

每個(gè) try 必須至少有一個(gè)提示。

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