php number_format函数的用法是什么

$number = 12345.6789;
$formatted_number = number_format($number); // 默认格式化为12346
$formatted_number = number_format($number, 2); // 格式化为12345.68
$formatted_number = number_format($number, 2, ",", "."); // 格式化为12,345.68