PHP 检测变量是否为空

PHP 中以下值得计算结果为 false：

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";
}

<?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";
}

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

<?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
}

<?php 
if (empty($var)) { ... }

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