1. Local scope

function update_counter()

{

  $counter++;//此处$counter为局部变量，与函数外的$counter非同一个

}

$counter = 10;

update_counter();

echo $counter;

//输出：10

2. Global scope

function update_counter()

{

  global $counter;//利用global关键字在函数内进行声明即可获取全局域的$counter

  $counter++;

}

$counter = 10;

update_counter();

echo $counter;

//输出： 11

function update_counter()

{

  $GLOBALS[counter]++;

}

$counter = 10;

update_counter();

echo $counter;

//输出：11

3. Static variables

function update_counter()

{

  static $counter = 0;//利用static关键字进行声明$counter，具有局部域

  $counter++;

echo "Static counter is now $countern";

}

$counter = 10;

update_counter();

update_counter();

echo "Global counter is $countern";

/*输出：

Static counter is now 1

Static counter is now 2

Global counter is 10

*/