PHP 检测变量是否为空

180it 2019-09-23 PM 1794℃ 0条

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 \r\n";

} else {

echo "string \"0\" is false \r\n"; // 输出:string "0" is false

}
if(empty($number)) {

echo "string \"0\" is false \r\n"; // 输出:string "0" is false

} else {

echo "string \"0\" is not false \r\n";

}

空数组:

<?php
$arr= array();
if($arr) {

echo 'array $arr is not false'."\r\n";

} else {

echo 'array $arr is false'."\r\n"; // 输出:array $arr is false

}
if(empty($arr)) {

echo 'array $arr is false'."\r\n"; // 输出:array $arr is false

} else {

echo 'array $arr is not false'."\r\n";

}

空对象在 PHP 5 以上版本中计算结果不为 false:

$obj=(object)array();
if($obj) {

echo '$obj is not false'."\r\n"; // 输出:$obj is not false

} else {

echo '$obj is false'."\r\n";

}
if(empty($obj)) {

echo '$obj is false'."\r\n";

} else {

echo '$obj is not false'."\r\n"; // 输出:$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 \r\n"; // 输出:string "0.0" is not false

} else {

echo "string \"0.0\" is false \r\n";

}
if(empty($number)) {

echo "string \"0.0\" is false \r\n";

} else {

echo "string \"0.0\" is not false \r\n"; // 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)) { ... }

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PHP 检测变量是否为空