Summarize the practical but easily overlooked knowledge in PHP (recommended)

This article mainly summarizes some useful little knowledge in PHP that is found in daily work but is easily ignored by people, such as whether the PHP function determines whether the function exists, the variable function of the PHP function, etc. Friends who need it, please follow the editor to take a look at the detailed introduction.

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

1. PHP functions 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.

function func() {
}
if (function_exists('func')){
 echo 'exists';
}

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

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

##2. Variable functions of PHP functions

The so-called variable function refers to calling a function through the value of a variable. Because the value of a variable is variable, different functions can be called 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 in object method calls

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

Static methods can also be called dynamically through variables

$func = 'getSpeed';
$className = 'Car';
echo $className::$func(); //动态调用静态方法

In static methods, the $this pseudo variable is not allowed to be used. You can use self, parent, static to call static methods and properties internally.

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 PHP classes and objects

Object comparison, when the same class When all attributes of two instances are equal, you can use the comparison operator == to judge. 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

Object copying, in some special cases, you can copy an object through the keyword clone, then the __clone method will be called, through this magic Method to set the value of a property.

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

There is a magical function in php, You can directly get the length of the string. This function is strlen().

$str = 'hello';
$len = strlen($str);
echo $len;//输出结果是5

The strlen function is very good at calculating English characters, but if there are Chinese characters, what should I do if I want to calculate the length?

You can use the mb_strlen() function to get the Chinese length in a string.

$str = "我爱你";
echo mb_strlen($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. PHP string formatting string

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 The string

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

Explain, 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 add escape characters to special characters and return a string

返回值：一个经过转义后的字符串

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

The above is the detailed content of Summarize the practical but easily overlooked knowledge in PHP (recommended). For more information, please follow other related articles on the PHP Chinese website!