php显示判断数组是不是带下标的二维数组

<?php
header("Content-type:text/html;charset=utf-8");
function va($value){
echo "<pre>";
var_dump($value);
echo "</pre>";
}
function edump($value){
va($value);
exit();
}
function jdump($value){
va($value);
echo json_encode($value,true);
exit();
}
$arr1 = array('a','b','c');
$arr2 = array(1=>'a',2=>'b',3=>'c');
//     jdump($arr1);
jdump($arr2);

array(3) {
[0]=>
string(1) "a"
[1]=>
string(1) "b"
[2]=>
string(1) "c"
}
["a","b","c"]

array(3) {
[1]=>
string(1) "a"
[2]=>
string(1) "b"
[3]=>
string(1) "c"
}
{"1":"a","2":"b","3":"c"}