PHP function scope and visibility

PHP function variable scope is divided into local (only within the function) and global (accessible within and outside the function). The visibility level (public, protected, private) determines the visibility of methods and properties to functions, ensuring encapsulation and code organization.

Scope and visibility of PHP functions

Scope

Scope of functions It refers to the scope that a variable can be used within or outside a function. Variables in PHP functions are either local variables or global variables.

Local variables

Local variables are declared and used within the function and are not accessible outside the function. Use the $ notation to declare local variables.

function myFunction() {
  $x = 5; // 局部变量
  echo $x; // 输出 5
}

// 尝试在函数外访问局部变量会报错
echo $x; // 报错: 未定义变量

Global variables

Global variables are declared and used outside the function and can also be accessed within the function. Use the global keyword to declare global variables.

$y = 10; // 全局变量

function myFunction() {
  global $y; // 声明全局变量
  echo $y; // 输出 10
}

myFunction(); // 调用函数

Visibility

Visibility determines the visibility of methods and properties in a class to functions. There are three visibility levels in PHP:

• public: Visible to all objects and functions
• protected: Visible to derived classes and parents Classes are visible
• private: Visible only to the class in which they are declared

Practical example

Consider an includeCustomer Programs for classes:

class Customer {
  private $name; // 私有属性
  public function getName() { // 公共方法
    return $this->name;
  }
}

// 在函数中访问私有属性 (报错)
function myFunction() {
  $customer = new Customer();
  echo $customer->name; // 报错: 无法访问私有属性
}

// 在函数中访问公共方法
function myOtherFunction() {
  $customer = new Customer();
  echo $customer->getName(); // 输出客户姓名
}

Conclusion

The scope and visibility of functions are important for organizing code and controlling access to variables and methods. Understanding these concepts is crucial to writing maintainable and clear PHP applications.

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