PHP must-learn knowledge points (little knowledge)

This article mainly summarizes some useful little knowledge in PHP and shares it for everyone’s reference and learning. Let’s take a look at the detailed introduction:

1. PHP function to determine whether the function exists

When we create a custom function and understand the usage of variable functions, in order to ensure that the function called by the program exists, we often use function_exists to determine whether the function exists. The same method_exists can be used to detect whether a class method exists.

<?php
function func() {
}
if (function_exists(&#39;func&#39;)){
 echo &#39;exists&#39;;
}
   ?>

Whether the class is defined can use class_exists

class MyClass{
}
// 使用前检查类是否存在
if (class_exists('MyClass')) {
 $myclass = new MyClass();
}

There are many such checking methods in PHP, such as whether the file exists file_exists, etc.

$filename = 'test.txt';
if (!file_exists($filename)) {
 echo $filename . ' not exists.';
}

2. Variable function of PHP function

The so-called variable function is to call the function through the value of the variable. Because the value of the variable is variable, it can Call different functions by changing the value of a variable. It is often used in callback functions, function lists, or to call different functions based on dynamic parameters. The method of calling a variable function is to add parentheses to the variable name.

function name() {
 echo 'jobs';
}
$func = 'name';
$func(); //调用可变函数

Variable functions can also be used to call methods on objects

class book {
 function getName() {
  return 'bookname';
 }
}
$func = 'getName';
$book = new book();
$book->$func();

Static methods can also be used through variables To make dynamic calls

$func = 'getSpeed';
$className = 'Car';
echo $className::$func(); //动态调用静态方法
   
//静态方法中，$this伪变量不允许使用。可以使用self，parent，static在内部调用静态方法与属性。  
class Car {
 private static $speed = 10;
  
 public static function getSpeed() {
  return self::$speed;
 }
  
 public static function speedUp() {
  return self::$speed+=10;
 }
}
class BigCar extends Car {
 public static function start() {
  parent::speedUp();
 }
}
 
BigCar::start();
echo BigCar::getSpeed();

3. Advanced features of objects between PHP classes and objects

Object comparison, when all attributes of two instances of the same class are equal When you need to judge whether two variables are references to the same object, you can use the congruence operator === to judge.

class Car {
}
$a = new Car();
$b = new Car();
if ($a == $b) echo '=='; //true
if ($a === $b) echo '==='; //false
对象复制，在一些特殊情况下，可以通过关键字clone来复制一个对象，这时__clone方法会被调用，通过这个魔术方法来设置属性的值。 
class Car {
 public $name = 'car';
  
 public function __clone() {
  $obj = new Car();
  $obj->name = $this->name;
 }
}
$a = new Car();
$a->name = 'new car';
$b = clone $a;
var_dump($b);

Object serialization, you can serialize the object into a string through the serialize method, which is used to store or transfer data, and then unserialize it when needed. The string is deserialized into an object for use.

class Car {
 public $name = 'car';
}
$a = new Car();
$str = serialize($a); //对象序列化成字符串
echo $str.&#39;<br>&#39;;
$b = unserialize($str); //反序列化为对象
var_dump($b);

4. Get the length of the string in PHP string

//php中有一个神奇的函数，可以直接获取字符串的长度，这个函数就是strlen()。
$str = 'hello';
$len = strlen($str);
echo $len;//输出结果是5
   
//strlen函数对于计算英文字符是非常的擅长，但是如果有中文汉字，要计算长度该怎么办？
//可以使用mb_strlen()函数获取字符串中中文长度。 
$str = "我爱你";
echo mb_strlen($str,"UTF8");//结果：3，此处的UTF8表示中文编码是UTF8格式，中文一般采用UTF8编码

5. The format of the PHP string Transforming strings

If there is a string $str = '99.9';, how to make this string become 99.90?

We need to use PHP's formatted string function sprintf()

Function description: sprintf (format, string to be converted)

Return: Formatted Please explain the string

$str = '99.9';
$result = sprintf('%01.2f', $str);
echo $result;//结果显示99.90

. What does the format

%01.2f in the above example mean?

1. This % symbol means the beginning. Writing it at the front means that the specified format has started. That is, the "start character", until the "conversion character" appears, the format ends.

2. What follows the % symbol is 0, which is a "fill-in-the-blank character", which means that if the position is empty, it will be filled with 0.

3. What follows 0 is 1. This 1 stipulates that all string occupancies must have more than 1 digit (the decimal point is also a digit).

If you change 1 to 6, the value of $result will be 099.90

Because there must be two digits after the decimal point, and 99.90 has a total of 5 placeholders. Now we need 6 placeholders, so fill them with 0s.

4. The .2 (point 2) after %01 is easy to understand. It means that the number after the decimal point must occupy 2 digits. If the value of $str is 9.234 at this time, the value of $result will be 9.23.

Why is 4 missing? Because after the decimal point, according to the above regulations, it must and can only occupy 2 digits. However, the value of $str occupies 3 digits after the decimal point, so the mantissa 4 is removed, leaving only 23.

5. Finally, end with f "conversion character".

6. PHP string escaping

php string escape function addslashes()

Function description: Used to escape special characters character, returns a string

Return value: an escaped string

$str = "what's your name?";
echo addslashes($str);//输出：what\'s your name?

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