About parameter problems with PHP foreach

$arr = array();foreach ($arr as $key => $value) {    if (!isset($key)) {        echo 'haha';    }}

When the $key does not exist, the output is haha, but the actual operation why does nothing output?

Reply content:

$arr = array();foreach ($arr as $key => $value) {    if (!isset($key)) {        echo 'haha';    }}

When the $key does not exist, the output is haha, but the actual operation why does nothing output?

No access to foreach

$keyHow is it that there is no way to be traversed?

Logic problem, definitely can't get into if

First the array is empty, does not enter foreach, and second, there is no !isset($key) case

Upstairs is right, your array is empty, the program will not enter the Foreach loop.

$arr has a value and does not enter the IF

$arr = array('key1'=>'hello',3,4=>'34',4);foreach ($arr as $key => $value) {    if (!isset($key)) {        echo 'haha';    }else{        echo $key.' ';    }}//print: key1 0 4 5

