PHP数字前补0的自带函数sprintf 和number_format的用法

<?php  
 //生成4位数，不足前面补0  
  $var=sprintf("%04d", 2);
  echo $var;//结果为0002  
  echo date('Y_m_d', time()).'_'.sprintf('d', rand(0,99));
  echo sprintf('%05s',444);//输出5为字符串，不足以0补充
?> 

<?php  
$number = 123;  
$txt = sprintf("%f",$number);  
echo $txt;  
?> 

<?php  
$number = 1234.56;

// english notation (default)
$english_format_number = number_format($number);
// 1,235

// French notation
$nombre_format_francais = number_format($number, 2, ',', ' ');
// 1 234,56

$number = 1234.5678;

// english notation without thousands seperator
$english_format_number = number_format($number, 2, '.', '');
// 1234.57
?>