直接上代码,如下:
/**
* isset:
* 判断一个变量是否存在,以及是否赋值
* unset:
* 释放一个变量,断开引用,会被垃圾回收器回收,该变量再次调用isset时,返回false
* empty:
* 判断一个变量是否为空,以及是否赋值
* 0 "0" null false "" array() 都是empty
*/
if (isset($s1)) {
echo "isset<br>";
} else {
echo "not set<br>";// will print
}
if (empty($s1)) {
echo "empty<br>";// will print
} else {
echo "not empty<br>";
}
if (empty("")) {
echo "empty<br>";// will print
} else {
echo "not empty<br>";
}
if (empty("0")) {
echo "empty<br>";// will print
} else {
echo "not empty<br>";
}
if (empty(array())) {
echo "empty<br>";// will print
} else {
echo "not empty<br>";
}
$s2 = 10;
if (isset($s2)) {
echo "is set<br>";// will print
} else {
echo "not set<br>";
}
unset($s2);//释放掉
if (isset($s2)) {
echo "is set<br>";
} else {
echo "not set<br>";// will print
}