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

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

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

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

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

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

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();

class Car {
}
$a = new Car();
$b = new Car();
if ($a == $b) echo '=='; //true
if ($a === $b) echo '==='; //false

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);

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

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

$str = "我爱你";
echo mb_strlen($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

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

$str = "what's your name";
echo addslashes($str);//输出：what\'s your name"color: #ff0000">总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助，如果有疑问大家可以留言交流，谢谢大家对的支持。