PHP中检查isset()和!empty()函数的必要性

bool isset( $var, mixed )

<?php 
  
$num = '0'; 
  
if( isset( $num ) ) { 
  print_r(" $num is set with isset function <br>"); 
} 
  
// 声明一个空数组 
$array = array(); 
   
echo isset($array['geeks']) ? 
'array is set.' : 'array is not set.'; 
?>

0 is set with isset function
array is not set.

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

0 is considered empty
1 is considered set

<?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"); 
}

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