$a=12.338938438;
echo sprintf("%.5f",$a) //结果：12.33894 


$a=12.3312356;
echo sprintf("%.5f",$a);//12.33124
echo sprintf("%f",$a);//331236  默认小数点后6位

$number = 1234.5678;

$english_format_number = number_format($number, 2, '.', '');
echo  $english_format_number ; // 1234.57

function getFloatValue($f,$len)
{
  $tmpInt=intval($f);

  $tmpDecimal=$f-$tmpInt;
  $str="$tmpDecimal";
  $subStr=strstr($str,'.');
  if(strlen($subStr)<$len+1)
 {
  $repeatCount=$len+1-strlen($subStr);
  $str=$str."".str_repeat("0",$repeatCount);

 }

  return    $tmpInt."".substr($str,1,1+$len);

}
echo getFloatValue(12.99,4) //12.9900
echo getFloatValue(12.9232555553239,4) //12.9232