PHP 检测变量是否为空

PHP 中以下值得计算结果为 false：

关键字	boolean	false
整型	integer	0
浮点型	double	0.0
字符串	string	""
字符串	string	"0"
数组	array	array()
对象	object	空对象 php<5
null	null	NULL

例如 字符串"0"：

<?php

$number = "0";
if($number) {
	echo "string "0" is not false 
";
} else {
	echo "string "0" is false 
"; // 输出：string "0" is false
}

if(empty($number))   {
	echo "string "0" is false 
"; // 输出：string "0" is false
} else {
	echo "string "0" is not false 
"; 
}

空数组：

<?php

$arr= array();

if($arr) {
	echo 'array $arr is not false'."
";
} else {
	echo 'array $arr is false'."
"; // 输出：array $arr is false
}

if(empty($arr))   {
	echo 'array $arr is false'."
"; // 输出：array $arr is false
} else {
	echo 'array $arr is not false'."
";
}

　　

空对象在 PHP 5 以上版本中计算结果不为 false：

$obj=(object)array();

if($obj) {
	echo '$obj is not false'."
"; // 输出：$obj is not false
} else {
	echo '$obj is false'."
";
}

if(empty($obj))   {
	echo '$obj is false'."
";
} else {
	echo '$obj is not false'."
"; // 输出：$obj is not false
}

　

注意：字符串"0.0"、字符串"00"、包括一个空格字符的字符串" "、字符串"false" 、整型 -1 都不为 false：

<?php

$number = "0.0";
if($number) {
	echo "string "0.0" is not false 
"; // 输出：string "0.0" is not false
} else {
	echo "string "0.0" is false 
";
}

if(empty($number))   {
	echo "string "0.0" is false 
";
} else {
	echo "string "0.0" is not false 
"; // 输出：string "0.0" is not false 
}

　　

正确地检查一个变量是否为空应该使用：

<?php

if (empty($var)) { ... }