Understanding PHP isset() and empty() Functions

The isset() function checks whether a variable is set and not null . Its signature is isset(mixed $var, mixed $... = ?): bool . It returns true if the variable exists and its value is not null , otherwise false . If a variable has been unset() , isset() will return false . When multiple arguments are passed, isset() returns true only if all arguments are set; evaluation stops at the first unset variable.

<code>&lt;?php
  $num = '0';
  if (isset($num)) {
      print_r("$num is set with isset");
  }
  echo "<br>";
  // Declare an empty array
  $array = array();
  echo isset($array['geeks']) ? 'array is set.' : 'array is not set.';
?&gt;</code>

Output: 0 is set with isset functionarray is not set.

The empty() function determines whether a variable is considered empty. Its signature is empty(mixed $var): bool . It returns true when the variable is not set, is null , an empty string, the integer 0 , the float 0.0 , the string "0" , false , an empty array, or an uninitialized variable; otherwise it returns false .

<code>&lt;?php
$temp = 0;
if (empty($temp)) {
    echo $temp . ' is considered empty';
}
echo "\n";
$new = 1;
if (!empty($new)) {
    echo $new . ' is considered set';
}
?&gt;</code>

Output: 0 is considered empty 1 is considered set

Both isset() and !empty() can be used to test variable existence, but empty() does not generate a warning when the variable does not exist, making it safer for such checks. Using both together can cause unnecessary performance overhead.

<code>&lt;?php
$num = '0';
if (isset($num)) {
    print_r($num . " is set with isset function");
}
echo "\n";
$num = 1;
if (!empty($num)) {
    print_r($num . " is set with !empty function");
}
?&gt;</code>

Output: 0 is set with isset function 1 is set with !empty function