从行转换为字符串（mysqli fetch_array）

I have a mysqli query that I want to convert to json.

tried:

$myArray = array();
while ($row = mysqli_fetch_array($result)) { 
    $myArray[] = $row;
}
$ot = json_encode($myArray);
print_r($ot); 

but got no results (blank line). If I print_r $myArray, there are values.

I can print out correct values on the while loop, so made another array and tried to add them, but neither of the following worked:

$mA []=array (alumnoX => $al1, grupox=> "two");
$mA []=array (alumnoX => (string)$al1, grupox=> "two");
$mA []=array (alumnoX => strval($al1), grupox=> "two");
$mA []=array (alumnoX => $row['alumno'], grupox=> "two");

How can I fix this?

edit -- (print_r of $myArray)

Array ( 
    [0] => Array ( 
              [0] => Martín 
              [alumno] => Martín 
              [1] => 1A 
              [grupo] => 1A 
              [2] => Computación básica 
              [materia] => Computación básica 
              [3] => sala cómputo cs 01 
              [salon] => sala cómputo cs 01 
              ) 
     [1] => Array ( 
              [0] => Martín 
              [alumno] => Martín 
              [1] => 1A 
              [grupo] => 1A 
              [2] => Introducción a la música 
              [materia] => Introducción a la música 
              [3] => Auditorio [salon] => Auditorio 
              ) 
      ) 

When using mysqli_fetch_array() will return an associative array and a numerically indexed array, which will duplicate all columns and confuse you and the json object. So use either mysqli_fetch_array($result,MYSQLI_ASSOC) or mysqli_fetch_assoc($result) so you only get the more useful associative array returned.

// assume you have code something like this
$result = mysql_query($con, $sql);
if ( ! $result ) {
    echo mysqli_error($con);
    exit;
}


$myArray = array();

//while ($row = mysqli_fetch_array($result)) { 
while ($row = mysqli_fetch_assoc($result)) { 
    $myArray[] = $row;
}
$ot = json_encode($myArray);

//print_r($ot); print_r() works on arrays and $ot is now a string
echo "<pre>$ot</pre>";

The data had some none conventional characters in it, after replacing:

json_encode($myArray );

to:

json_encode($myArray, JSON_UNESCAPED_UNICODE );

It worked as expected.