php float不四舍五入截取浮点型字符串的方法

$a=12.338938438; 
echo sprintf("%.5f",$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