$.ajax({
    url: "src/php/ajax.php",
        data:{solicitud:"prueba"},
        type: "POST",
    dataType: "json",
        success:function(data){
            var availableTags = data;
        $( "#tags" ).autocomplete({
            source: availableTags
        });
    }
});

/*****************************************************/

 $sql_giros="SELECT * FROM `t_giros_emp`";
        $query_giros=mysql_query($sql_giros,$link);
        $stack = array();
        while($giro=mysql_fetch_array($query_giros)){
            array_push($stack,ucfirst(strtolower(($giro['c_descr_giro']))));
        }
        echo json_encode($stack);