PHP determines whether it is an empty string

Method 1: Use $_MODULE['variable name']

if($_MODULE['var']) {
     // 这是表示已经输入了值
}
 
else {
     // 这里表示未输入值
}

Method 2: Assign the value first, and then use empty to judge.

Note: Any uninitialized variable, a variable with a value of 0 or false or an empty string "" or null, an empty array, or an object without any attributes will be judged as empty==true

Note 1: Uninitialized variables can also be detected as "empty" by empty

Note 2: empty can only detect variables, not statements

$a = 0;
$b = '';
$c = array();
if (empty($a)) echo '$a 为空' . "";
if (empty($b)) echo '$b 为空' . "";
if (empty($c)) echo '$c 为空' . "";
if (empty($d)) echo '$d 为空' . "";

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