I searched and tried anyway to implement the behaviour that i searched in my question but i didn't find nothing. I supposed that, like you can see in this answer, unset function adds indices to the array because the JSON_encode not support arrays with hole. So, to solve my problem, i load the JSON file with a jQuery function, delete the elements with jQuery and i call a ajax function to delete the files linked at the address contained in the json file:
$.getJSON('loadauto.json', function(result) {
var y = result;
$.each(result, function(i, field){
if(field.indirizzo_paginaauto == x){
delete result[i];
}
});
$.ajax({
async: true,
cache: false,
type: 'POST',
url: 'deleteauto.php',
data: { nuovofilejson: y, indirizzo: x},
success: function(data) {
alert ("Auto cancellata definitivamente");
},
error: function(data) {
alert ("Error");
}
});
}