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今天小編給大家分享一下PHP面試題問答題有哪些的相關知識點，內容詳細，邏輯清晰，相信大部分人都還太了解這方面的知識，所以分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后有所收獲，下面我們一起來了解一下吧。
話題: PHP
困難: ?
如果是兩個不同的類型，運算符 == 則在兩個不同的類型之間進行強制轉換
=== 操作符執行’類型安全比較‘
這意味著只有當兩個操作數具有相同的類型和相同的值時，它才會返回 TRUE。
1 === 1: true 1 == 1: true 1 === "1": false // 1 是一個整數, "1" 是一個字符串 1 == "1": true // "1" 強制轉換為整數，即1 "foo" === "foo": true // 這兩個操作數都是字符串，并且具有相同的值
? 源自: stackoverflow.com
話題: PHP
困難: ?
為了能夠通過引用傳遞變量，我們在其前面使用 &，如下所示：
$var1 = &$var2
? 源自: guru99.com
話題: PHP
困難: ?
$GLOBALS 是關聯數組，包含對腳本全局范圍內當前定義的所有變量的引用。
? 源自: guru99.com
話題: PHP
困難: ?
PHP 允許用戶使用 ini_set () 修改 php.ini 中提到的一些設置。此函數需要兩個字符串參數。第一個是要修改的設置的名稱，第二個是要分配給它的新值。
給定的代碼行將啟用腳本的 display_error 設置 (如果它被禁用)。
ini_set('display_errors', '1');
我們需要將上面的語句放在腳本的頂部，以便該設置一直保持啟用狀態，直到最后。此外，通過 ini_set () 設置的值僅適用于當前腳本。此后，PHP 將開始使用 php.ini 中的原始值。
? 源自: github.com/Bootsity
話題: PHP
困難: ??
require() 函數與 include() 函數相同，只是它處理錯誤的方式不同。如果出現錯誤，include() 函數會生成警告，但腳本會繼續執行。require() 函數會產生致命錯誤，腳本會停止。
我的建議是 99.9% 的時間里只使用 require_once。
使用 require 或 include 代替意味著您的代碼在其他地方不可重用，即您引入的腳本實際上是在執行代碼，而不是提供類或某些類功能庫。
? Source: stackoverflow.com
主題: PHP
難度: ??
stdClass 只是將其他類型強制轉換為對象時使用的通用” 空’’類。stdClass 不是 PHP 中對象的基類。這可以很容易地證明:
class Foo{}
$foo = new Foo();
echo ($foo instanceof stdClass)?'Y':'N'; // 輸出'N'對于匿名對象，動態屬性等很有用。
考慮 StdClass 的一種簡單使用場景是替代關聯數組。請參見下面的示例，該示例顯示 json_decode() 如何允許獲取 StdClass 實例或關聯數組。
同樣但未在本示例中顯示的 SoapClient::__soapCall 返回一個 StdClass 實例。
//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? 源自: stackoverflow.com
話題: PHP
困難: ??
沒有區別，它們是一樣的。 選擇 die() 而不是 exit() 的唯一好處可能是你節省了額外鍵入一個字母的時間.
? 源自: stackoverflow.com
話題: PHP
困難: ??
const 和 define 的根本區別在于，const 在編譯時定義常量，而 define 在運行時定義常量。
const FOO = 'BAR';
define('FOO', 'BAR');
// but
if (...) {
const FOO = 'BAR'; // 無效
}
if (...) {
define('FOO', 'BAR'); // 有效
}同樣在 PHP 5.3 之前，const 命令不能在全局范圍內使用。你只能在類中使用它。當你想要設置與該類相關的某種常量選項或設置時，應使用此選項。或者你可能想要創建某種枚舉。一個好的 const 用法的例子是擺脫了魔術數字。
Define 可以用于相同的目的，但只能在全局范圍內使用。它應該僅用于影響整個應用程序的全局設置。
除非你需要任何類型的條件或表達式定義，否則請使用 consts 而不是 define()—— 這僅僅是為了可讀性！
? 源自: stackoverflow.com
話題: PHP
困難: ??
array_key_exists 它會告訴你數組中是否存在鍵，并在 $a 不存在時報錯。
如果 key 或變量存在且不是 null，isset 才會返回 true。當 $a 不存在時，isset 不會報錯。
考慮:
$a = array('key1' => 'Foo Bar', 'key2' => null);
isset($a['key1']); // true
array_key_exists('key1', $a); // true
isset($a['key2']); // false
array_key_exists('key2', $a); // true? 源自: stackoverflow.com
話題: PHP
困難: ??
var_dump 函數用于顯示變量 / 表達式的結構化信息，包括變量類型和變量值。數組遞歸瀏覽，縮進值以顯示結構。它還顯示哪些數組值和對象屬性是引用。
print_r() 函數以我們可讀的方式顯示有關變量的信息。數組值將以鍵和元素的格式顯示。類似的符號用于對象。
考慮:
$obj = (object) array('qualitypoint', 'technologies', 'India');var_dump($obj) 將在屏幕的輸出下方顯示:
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
話題: PHP
困難: ??
notice 不是一個嚴重的錯誤，它說明執行過程中出現了一些錯誤，一些次要的錯誤，比如一個未定義的變量。
當出現更嚴重的錯誤，如 include () 命令引入不存在的文件時，會給出警告 warning。 這個錯誤和上面的錯誤發生，腳本都將繼續。
fatal error 致命錯誤將終止代碼。未能滿足 require () 將生成這種類型的錯誤。
? 源自: pangara.com
話題: PHP
困難: ??
檢查 php.ini 中的 “display_errors” 是否等于 “on”，或者在腳本中聲明 “ini_set('display_error',1)”。
然后，在你的代碼中包含 “ERROR_REPORTING(E_ALL)”，以便在腳本執行期間顯示所有類型的錯誤消息。
? 源自: codementor.io
話題: PHP
困難: ??
思考:
function showMessage($hello = false){
echo ($hello) ? 'hello' : 'bye';
}? 源自: codementor.io
話題: PHP
困難: ??
PHP 只支持單一繼承；這意味著使用關鍵字’extended’只能從一個類擴展一個類。
? 源自: guru99.com
話題: PHP
困難: ??
在 PHP 中，通過值傳遞的對象。
? 源自: guru99.com
話題: PHP
困難: ??
!= 表示 不等于 (如果 $a 不等于 $b，則為 True)， !== 表示 不全等 (如果 $a 與 $b 不相同，則為 True).
? 源自: guru99.com
話題: PHP
困難: ??
PDO 代表 PHP 數據對象。
它是一組 PHP 擴展，提供核心 PDO 類和數據庫、特定驅動程序。它提供了供應商中立、輕量級的數據訪問抽象層。因此，無論我們使用哪種數據庫，發出查詢和獲取數據的功能都是相同的。它側重于數據訪問抽象，而不是數據庫抽象。
? 源自: github.com/Bootsity
Topic: PHP
Difficulty: ??
當程序執行出現異常報錯時，后面的代碼將不會再執行，這時 PHP 將會嘗試匹配第一個 catch 塊進行異常的處理，如果沒有捕捉到異常程序將會報致命錯誤并顯示”Uncaught Exception”。
可以在 PHP 中拋出和捕獲異常。
為了處理異常，代碼可以被包圍在”try” 塊中.
每個 try 必須至少有一個對應的 catch 塊 。多個不同的 catch 塊可用于捕獲不同類的異常。
在 catch 塊中也可以拋出異常（或重新拋出之前的異常）。
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
Topic: PHP
Difficulty: ??
echo 和 print 基本上是一樣的。他們都是用來打印輸出數據的。
區別在于:
echo 沒有返回值，而 print 的返回值為 1，因此 print 可以在表達式中使用。
echo 可以接受多個參數一起輸出 (但是這種多個的輸出方式很少見)，而 print 一次只可以輸出一個參數。
echo 的輸出比 print 效率要高一些 .
? Source: github.com/Bootsity
Topic: PHP
Difficulty: ???
require_once() 作用與 require() 的作用是一樣的，都是引用或包含外部的一個 php 文件，require_once() 引入文件時會檢查文件是否已包含，如果已包含，不再包含 (require) 它。
我建議在 99.9% 的時候要使用 require_once
使用 require 或 include 意味著您的代碼不可在其他地方重用，即您要拉入的腳本實際上是在執行代碼，而不是提供類或某些函數庫。
? Source: stackoverflow.com
Topic: PHP
Difficulty: ???
思考:
function has_string_keys(array $array) {
return count(array_filter(array_keys($array), 'is_string')) > 0;
}如果 $array 至少有一個字符串類型的 key ，它將被視為關聯數組。
? Source: stackoverflow.com
Topic: PHP
Difficulty: ???
這里有幾種實現方法：
使用 Ajax 從服務端獲取你需要的數據。
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 一個請求對象
oReq.onload = function() {
// 在這里你可以操作響應數據
// 真實的數據來自 this.responseText
alert(this.responseText); // 將提示: 42
};
oReq.open("get", "get-data.php", true);
// ^ 不要阻塞的其余部分執行。
// 不要等到請求結束再繼續。
oReq.send();
</script>可以在網頁任何地方輸出數據，然后使用 JavaScript 從 DOM 中獲取信息.
<div id="dom-target" style="display: none;">
<?php
$output = "42"; // 此外, 做一些操作，獲得 output.
echo htmlspecialchars($output); /* 你必須避免特殊字符，不然結果將是無效HTML。 */
?>
</div>
<script>
var div = document.getElementById("dom-target");
var myData = div.textContent;
</script>直接在 JavaScript 代碼中 echo 數據。
<script>
var data = <?php echo json_encode("42", JSON_HEX_TAG); ?>; // Don't forget the extra semicolon!
</script>? Source: stackoverflow.com
Topic: PHP
Difficulty: ???
PHP 數組通過復制進行賦值，而對象通過引用進行賦值。所有默認情況下，PHP 將復制這個數組。這里有一個 PHP 參考，一目了然：
$a = array(1,2); $b = $a; // $b 是一個不同的數組 $c = &$a; // $c 是 $a 的引用
? Source: stackoverflow.com
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
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
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 except that 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
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
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
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
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 ?? $placeholder ?? "Guest";
? Source: github.com/Bootsity
Topic: PHP
Difficulty: ???
Recovering from Error is not possible. The only solution to errors is to terminate the execution. Where as you can recover from Exception by using either try-catch blocks or throwing exception back to caller.
You will not be able to handle the Errors using try-catch blocks. Even if you handle them using try-catch blocks, your application will not recover if they happen. On the other hand, Exceptions can be handled using try-catch blocks and can make program flow normal if they happen.
Exceptions are related to application where as Errors are related to environment in which application is running.
? Source: github.com/Bootsity
Topic: PHP
Difficulty: ???
There are following functions which can be used from Exception class.
getMessage() ? message of exception
getCode() ? code of exception
getFile() ? source filename
getLine() ? source line
getTrace() ? n array of the backtrace()
getTraceAsString() ? formated string of trace
Exception::__toString gives the string representation of the exception.
? Source: github.com/Bootsity
Topic: PHP
Difficulty: ???
Non parameterised functions don’t take any parameter at the time of calling.
Parameterised functions take one or more arguments while calling. These are used at run time of the program when output depends on dynamic values given at run time There are two ways to access the parameterised function:
call by value: (here we pass the value directly )
call by reference: (here we pass the address location where the value is stored)
? Source: github.com/Bootsity
Topic: PHP
Difficulty: ???
In case of call by reference, actual value is modified if it is modified inside the function. In such case, we need to use & symbol with formal arguments. The & represents reference of the variable.
Example:
function adder(&$str2) {
$str2 .= 'Call By Reference';
}
$str = 'This is ';
adder($str);
echo $str;Output:
This is Call By Reference
? Source: github.com/Bootsity
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; $c = Horse
? Source: github.com/Bootsity
Topic: PHP
Difficulty: ????
Consider this code:
public function getTotal($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
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
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
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
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
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
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
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
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
$student= Student::create()->setFirstName("John")->setLastName("Doe");? Source: stackoverflow.com
Topic: PHP
Difficulty: ?????
You cannot overload PHP functions. Function signatures are based only on their names and do not include argument lists, so you cannot have two functions with the same name.
You can, however, declare a variadic function that takes in a variable number of arguments. You would use func_num_args() and func_get_arg() to get the arguments passed, and use them normally.
Consider:
function myFunc() {
for ($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
為了處理異常，代碼可能被包圍在一個 try 塊中。
每個 try 必須至少有一個提示。
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