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 $counter\n";
}
$counter = 10;
update_counter();
update_counter();
echo "Global counter is $counter\n";
/*输出：
Static counter is now 1
Static counter is now 2
Global counter is 10
*/
