php variable scope

* There are only three scopes:

* 1. Global: Created outside the function, only used in the current script except for the function;

* 2. Local: Created inside the function, can only be used in the function, not accessible externally;

* 3. Static: Created inside the function, only used in the function, its value will not be lost after the function is executed;

$siteName = 'PHP中文网'; //全局变量

//The global variable automatically becomes a key-value pair in the global variable array, and the key corresponds to the variable

$GLOBALS['siteName']='PHP中文网'; //全局变量替代语法

* Function: It is a code segment with a specific function in the script, which can be called repeatedly

* 1. Basic syntax:

* 1.1 Function declaration: function funcnName($args){ #code...}

* 1.2 Function expression: $funcName = function ( $ages){ #code...}

* 2. Call:

* 2.1 Call by name: funcName($args) / $funcName($args)

* 2.2 Self-calling: declaration and calling are completed at the same time

* (function (args){ #code...})()

function hello()
{
  global $siteName; //引用全局变量,使用全局变量数组,不必声明引入
  $userName = 'Peter Zhu'; //局部变量
  // return '欢迎来到'.$siteName.',我是:'.$userName;
  return '欢迎来到'.$GLOBALS['siteName'].',我是:'.$userName;
}
echo hello();  //函数调用
echo '
';

//Static variables must and can only be used in Declared and used in the function

function myStatic()
{
  static $num = 1;
  //$num++,先将$num值输出后再加1
  return '第'.$num.'次输出'.$num++.'
';
}
echo '第一次执行完成后$num值:'.myStatic().'
';

//After the first execution is completed, the value of $num is 2

echo '第一次执行完成后$num值:'.myStatic().'
';

//After the second execution is completed, $ The num value is 3

echo '第一次执行完成后$num值:'.myStatic().'
';

//After the third execution, the $num value is 4

echo '第一次执行完成后$num值:'.myStatic().'
';

* Super global variables: $_SERVER, $_COOKIE, $_SESSION, $_GET, $_POST ,$_REQUEST

* 1. They are predefined variables, all are arrays, and can be used as they come, no declaration is required;

* 2. Cross-scope, both globally and locally (inside the function) ) can be used directly;

* 3. Cross-scope is not cross-script. The so-called super global, including global, refers to the current script file.

echo '
';

//Can be referenced directly globally

echo '我的姓名是:'.$_GET['name'];

//Can also be referenced directly in the function

function sayName()
{
  //超全局变量不需要使用关键字 global 进行声明
  return '我的姓名是:'.$_GET['name'];
}

//Call the function

echo sayName();