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round

(PHP 3, PHP 4, PHP 5)

round -- 对浮点数进行四舍五入

说明

float round ( float val [, int precision] )

返回将 val 根据指定精度 precision（十进制小数点后数字的数目）进行四舍五入的结果。precision 也可以是负数或零（默认值）。

例子 1. round() 例子

<?php
echo round(3.4);         // 3
echo round(3.5);         // 4
echo round(3.6);         // 4
echo round(3.6, 0);      // 4
echo round(1.95583, 2);  // 1.96
echo round(1241757, -3); // 1242000
echo round(5.045, 2);    // 5.05
echo round(5.055, 2);    // 5.06
?>

注: PHP 默认不能正确处理类似 "12,300.2" 的字符串。见字符串转换为数值。

注: precision 参数是在 PHP 4 中被引入的。

参见 ceil()，floor() 和 number_format()。


add a note add a note User Contributed Notes
dave at koales dot co dot uk
30-Oct-2006 09:39
Note, there is a bug in what appears to be the Windows implementation.  See http://bugs.php.net/bug.php?id=36008 for more information and a fix (convert the number to a string before rounding).
maxteiber at gmail dot com
16-Oct-2006 08:15
the result of this function always depends on the underlying C function. There have been a lot of compiler bugs and floating-point precission problems involving this function. Right now the following code:

<?php
echo round(141.075, 2);
?>

returns:

141.07

on my machine.
So never really trust this function when you do critical calculations like accounting stuff!
Instead: use only integers or use string comparisons.
Hitlers Pet Gerbil
05-Oct-2006 04:47
In response to boonedocks at gmail dot com

Your calculations are slightly incorrect. You only use the formula when the 1/1000 position is equal to 5, otherwise you follow standard rounding proceedures.

I wrote a quick snippet which works with the input as a string, uses inline substrings and substitutions. Works VERY fast.

<?php
function bankers_round ($moneyfloat = null)
{
   $money_str = sprintf("%01.3f", round($moneyfloat, 3)); // convert to rounded (to the nearest thousandth) string
   $thous_pos = strlen($money_str)-1;                    // Thousandth string position
   $hundt_pos = strlen($money_str)-2;                    // Hundredth string position
   if ($money_str[$thous_pos] === "5") $money_str[$thous_pos] = ((int)$money_str[$hundt_pos] & 1) ? "9" : "0"; // use a bitwise test, its faster than modulus
   // The above statement assists round() by setting the thousandth position to 9 or zero if the hundredth is even or odd (respectively)

   return round($money_str, 2); // Return rounded value
}

?>

Hitlers Pet Gerbil
ionut dot socol at euromarket dot ro
12-Aug-2006 06:40
My name is Ionut Socol and i'm from Romania

A small script that allow you to round up, round down or just return the integer number.
The $direction value cand be:
0  - rounding down
1 - rounding up
any thing else for returning the integer value

<?php
function rounding($no,$direction)
   {                            $skip=0;
   if(is_float($no) and $direction = 1)
       {
       $exploded = explode(".",$no);
       $nrr = $exploded[0]+1;    $skip=1;
       }
 
   if(is_float($no) and $direction = 0)
       {
       $exploded = explode(".",$no);
       $nrr = $exploded[0];        $skip=1;
       }

   if(!is_float($no) and $skip ==1) { $nrr = $nrr; } else { $nrr = floor($nrr); }

     return $nrr;
   }
?>
12-Jul-2006 01:48
Since everybody here seems to be occupied wanking over their selfmade round() functions, a little note about the actual php-implementation:
If you round() a _very_ small number to a reasonable number of decimals, it will retain its sign! IE:

round(1.4 - 1.4, 4) returns "-0" instead of just "0"!

Dont ask me how to properly get rid of this. Im just gonna cut it off
using preg_replace().
milosz_jablonski at yahoo dot co dot uk
11-May-2006 11:51
function round is more than just fantastic. Why not to use this one instead of creating your own for rounding UP/DOWN

$proc_total1 had a number of values (see 2 examples below)

round($proc_total1)  //$proc_total1=57.1428571429
echo $proc_total1;    //57

round($proc_total1)  //$proc_total1=42.8571428571
echo $proc_total1;    //43

good luck
Mazzu
11-May-2006 04:41
Another correction to the significant digits formula :

($n == 0) ? 0 : round($n, floor(0 - log10(abs($n))) + $sysdigits)

- In order to handle zero and negative numbers
- Use floor() instead of ceil() to do not substract 1
adrianbj
16-Feb-2006 04:19
A simple correction to the significant digits formula posted way below:

round($n, ceil(0 - log10($n)) + $sigdigits - 1);

Note the addition of '-1' to the formula originally posted.
28-Jan-2006 04:41
Instead of writing roundDown() and roundUp() functions in php, you might want to consider floor() and ceil(), as they are probably much, much faster.
reinhard at ess dot co dot at
26-Jan-2006 11:56
the same is true for round_down

function round_down($value){
   list($val,$dummy) = explode(".",$value);
   return $val;
}
reinhard at ess dot co dot at
26-Jan-2006 11:54
I have made the round_up-function much more simpler and useable of any values (float or int) -> if no decimal values then the value is taken else we add one to the value in front of the dot ;)

function round_up($value){
   list($val,$dummy) = explode(".",$value);
   return $dummy?$val+1:$val;
}
elbekko at gmail dot com
24-Jan-2006 05:45
I created a round down function, pretty basic but it should work :P

<?php
function round_down($value)
   {
   if(is_float($value))
       {
       $exploded = explode(".",$value);
       return $exploded[0];
       }
   else
       {
       die("Only float values can be entered.");
       }
   }
?>

You could use the same function for rounding up:

<?php
function round_up($value)
   {
   if(is_float($value))
       {
       $exploded = explode(".",$value);
       return $exploded[0] + 1;
       }
   else
       {
       die("Only float values can be entered.");
       }
   }
?>
php dot net at cdauth dot de
23-Jan-2006 04:33
Beware that the implementation posted below:
<?php
$number = 254.51263;
$round = (int)($number+0.5); // 255
?>
does not work with very large numbers.
boonedocks at gmail dot com
14-Jan-2006 05:08
Since PHP no longer does Banker's Rounding, I came up with an implementation here:

http://boonedocks.net/mike/archives/106-Bankers-Rounding-for-PHP.html

It hasn't really been hammered on, so testing and comments are welcome.
adrenalin at bmxstyle dot com
19-Dec-2005 09:42
Oh sorry, I had mistake in a simple version of the script. Here is a working and tested version:

<?php
function divby($val, $by) {
  
   $val -= $val % $by;
  
   return $val;
}
?>

But in blackhole's description is a little mistake, because if I try: divby(-23, 10); it will return -20, because $val is negative so the result must be negative too.
adrenalin at bmxstyle dot com
19-Dec-2005 06:31
Here is a simple version of blackhole's script.

<?php
function divby($val, $by) {
 
  $val -= abs($val) % $by;
  
   return $val;
}
?>
blackhole at ggot dot org
22-Sep-2005 08:01
Sometimes you will want to make a number divisible by another (like rounding by 5s, or 10s, or 7s, or 1438s, or whatever) instead of just making it divisble by one such as round() with only one argument.  The function that follows is fairly simply and behaves mostly as expected.

<?php
function divby($val, $by) {
   if ($val < 0)
   $val += -$val % $by;
   else
   $val -= $val % $by;
  
   return $val;
}
?>

divby(23, 10) will return 20
divby(77, 5) will return 75
divby(138, 7) will reuturn 133
divby(-23, 10) will return 20

note: the only way to return a negative value is to make BOTH values negative, for example:

divby(-25, -10) will return -20

note also: if the value of $by is greater than $val then the function will return 0, for example:

divby(3, 4) will return 0
divby(4, 3) will return 3
twain47 at gmail dot com
10-May-2005 10:25
The bankers' rounding behaviour mentioned in the notes below seems to have been changed to normaly rounding. 

From the comments in http://bugs.php.net/bug.php?id=24142 it was changed in 4.3.0 but various bugs seem to have been introduced and it wasn't stable again until 4.3.5 (http://bugs.php.net/bug.php?id=25694)
roger dot anzoategui at gmail dot com
07-Apr-2005 12:14
Ron, very good observation, in some occasions the behavior of an accounting system in which I participated, the following problem occurred: reduces it of two exact values did not give zero due to that millionths of difference in the decimals they existed (not yet itself if due to the own algorithms of the microprocessor or of the language, did not I have the opportunity to do a bench, and the surest thing is that this Reason that may not have been able to notice me previously).
Your observation I have it present in my code.
ron at korving dot demon dot nl
11-Feb-2005 06:46
Unfortunately, ranzoategui's (and my revision) round version did not work well (try to round 8.075 to 2 decimals for example).

I found out the best way to achieve a good round is to add a tiny number to the value before rounding. This seems to work fine in all cases (and luckily it's faster than previous methods):

<?
  function stdround($num, $d=0)
  {
   return round($num + 0.0001 / pow(10, $d), $d);
  }
?>
10-Feb-2005 10:23
If you want more speed, and you dont need any decimals returned, use this:
<?php

$number = 254.51263;
$round = (int)($number+0.5); // 255

?>
This way is 32% faster than calling the round() function in this situation (tested!).
ron at korving dot demon dot nl
07-Feb-2005 10:12
This is a slighty shorter and faster version of ranzoategui's round function:

<?
  function stdround($num, $d=0)
  {
   $d = pow(10, $d);
   return round(floor($num * $d * 10) / 10) / $d;
  }
?>

This function behaves exactly like round(), except for the fact that it doesn't apply a so called bankers' rounding algorithm, but a more classic approach (where a 5 is always rounded up).

For more info on Banker's rounding: http://en.wikipedia.org/wiki/Significance_arithmetic
ranzoategui at bolivia dot com
07-Jan-2005 04:16
<?php
/*
 * @abstract This function is very useful to round totals with definite decimals.
 *
 * @param float  $value
 * @param integer $dec
 * @return float
 */
  function approx( $value, $dec = 2 ) {
     $value += 0.0;
     $unit  = floor( $value * pow( 10, $dec + 1 ) ) / 10;
     $round = round( $unit );
     return $round / pow( 10, $dec );
  }

// Example
// $round = approx( 3.14159, 4 ); // This result 3.1416
?>
martin at chinese-monkey dot com
14-Nov-2004 01:16
If you didn't want to use 'ceil()' or 'floor()' as it only rounds to a whole number u could do this:

<?php
$actual_value = 3.352;
$number = 0.01; //how many decimal places you want it to be

$temp1 = $actual_value * 2;
$temp2 = $temp1 + $number; //'+ $number' if rounding up '- $number' if rounding down
$temp3 = $temp2 / 2;
$new_value = round($temp3, 2);

echo $new_value; // 3.36
?>
red at aztec dot sk
19-Jul-2004 08:21
Better is:

<?php
   $actual_value = 3.45;              // 3.45
   $half_round = round(($actual_value*2), 0)/2; // 3.5
?>

or
<?php
   $actual_value = 3.45;              // 3.45
   $temp1 = $actual_value * 2;        // 6.9
   $temp2 = round($temp1, 0);  // 7
   $half_round = $temp2 / 2            // 3.5
?>

NOT
<?php
   $actual_value = 3.45;              // 3.45
   $temp1 = $actual_value * 2;        // 6.9
   $temp2 = round($actual_value, 0);  // 7
   $half_round = $temp2 / 2            // 3.5
?>
Dan
07-Jul-2004 05:08
a simpler solution to the 'round to a half' method suggested by monte at ispi dot net, below. This version returna the actual number.

<?php
   $actual_value = 3.45;              // 3.45
   $temp1 = $actual_value * 2;        // 6.9
   $temp2 = round($actual_value, 0);  // 7
   $half_round = $temp2 / 2            // 3.5
?>
monte at ispi dot net
29-Jun-2004 09:31
Just a quick note on rounding to the nearest "half" instead of nearest "whole". I my case, I'm showing a user rating with stars and need to show a star for each whole, and half a star for remainder values closer to half than whole.

// replace 3.45 with any rating
$_actual_rating = 3.45;

$_rating_round_half = round($_actual_rating / 0.5) * 0.5;
$_remainder = fmod($_rating_round_half, 1);

$_rating = (int) $_rating_round_half - $_remainder;
$_half_star = $_remainder == 0.5;

In the above example, $_rating will contain a whole number for the number of stars to display, and $_half_star will be a boolean to determine whether or not to display half a star as well.
ga dot N-O-S-P-A-M at lacde dot net
15-Apr-2004 01:49
If you want a complete and simple solution to round for n digits you should use this function at the bottom.
(you may want this to be even clearer with nice defines like below but it is not obliged if you use -1/0/1)
<?php
define(FLOOR,-1);
define(NEARER,0);
define(CEIL,1);
?>

$myNiceValue=MyApprox($value,3); <- nearest value for 3 digits
$myNiceValue=MyApprox($value,3,FLOOR); <- floor value

ex:
MyApprox(2.36745,3); // 2.37
MyApprox(1462.36745,3); // 146 (because nearer)
MyApprox(1465.36745,3); // 147 (because nearer)
MyApprox(1462.36745,3,FLOOR); // 146
MyApprox(1462.36745,3,CEIL); // 147

MyApprox(-1462.36745,3); // -146 (because nearer)
MyApprox(-1465.36745,3); // -147 (because nearer)
MyApprox(-1462.36745,3,FLOOR); // -147 <-- like PHP but for n digit
MyApprox(-1462.36745,3,CEIL); // 146 <-- like PHP but for n digit

The last argument ($inverseNeg) is provided only if you want to switch floor and ceil for negative value to overide the common behaviour of php. (little chances it would be useful for you)

This must work for php > 4.0.5
if you want to make it work for < versions you may only have to change the str_replace to do not use arrays but 2 str_replace instead.

It may be really interesting to have this kind of functions directly in php !

Plz note that this one is probably not the quicker code possible I coded it quickly. (if you need speed it's better to use directly the method you want anyway)

Note that it's simple to use a "common" behavior in your script(s) :
define(APPROX_METHOD,-1)

MyApprox($value,$n,APPROX_METHOD);
...

So you can change once for all the method or even by choice of your user.

<?php
function MyApprox($fValue,$sigdigits=0,$mode=0,$inverseNeg=0)
// mode=-1 gives floor
// mode=0 (default) gives automatic Round to nearest digit : >5 -> +1
// mode=1 gives ceil
// inverseNeg=0 (default)-> PHP floor/ceil behavior, floor(-2.3)=-6, floor towards -INF
// inverseNeg=1 -> inverse floor/ceil behavior means floor(-2.3)=-5, floor towards 0 in case of need
{
   $sValue=''.(float)($fValue);
   $lenght=strlen($sValue);
   $isNeg=$fValue<0;
   if(($sigdigits<=0)||($sigdigits==False))
     {
       if(($inverseNeg)&&($isNeg)) $mode=-$mode;
       if($mode==-1) return floor($fValue);
       if($mode==1) return ceil($fValue);
       return round($fValue);
     }
  
   $posDot=strpos($sValue,'.'); 
   $sResult=str_replace(array('.','-'),'', $sValue);
   $fResult=0.0;
   if(($mode==0)&&(intval($sResult{$sigdigits})>=5)) $fResult=1.0;
   $sResult=substr($sResult,0,$sigdigits);
  
   $fResult+=(float)$sResult;
   if($isNeg)
     {
       if($inverseNeg)
         {
           if($mode==1) $fResult+=1;
         }
       else if($mode==-1) $fResult+=1;
     }
   else if($mode==1) $fResult+=1;
  
   if($posDot==False) $posDot=$lenght;
   $numb=$sigdigits-($posDot-$isNeg);
   if($numb>0) for($i=0;$i<$numb;$i++) $fResult/=10.0;
   else if($numb<0) for($i=0;$i<$numb;$i++) $fResult*=10.0;
   if($isNeg) return -$fResult;
   else return $fResult;
}
?>
terry at scribendi dot com
13-Jan-2004 03:45
To round any number to a given number of significant digits, use log10 to find out its magnitude:

round($n, ceil(0 - log10($n)) + $sigdigits);

Or when you have to display a per-unit price which may work out to be less than a few cents/pence/yen you can use:

// $exp = currency decimal places - 0 for Yen/Won, 2 for most others
$dp = ceil(0 - log10($n)) + $sigdigits;
$display = number_format($amount, ($exp>$dp)?$exp:$dp);

This always displays at least the number of decimal places required by the currency, but more if displaying the unit price with precision requires it - eg: 'English proofreading from $0.0068 per word', 'English beer from $6.80 per pint'.
ssttoo at hotmail dot com
06-Dec-2003 08:12
Having done the following test:
<?php
$test_numbers = array (1.255,3.255,10.255);
foreach ($test_numbers AS $number){
   echo "<br />Number:<b> " . $number . "</b>";
   echo "<br />Printf():<b> ";
   printf("%.2f",$number);
   echo "</b><br />Printf() and round(): <b> ";
   printf("%.2f",round($number,2));
   echo "</b><br />Printf() and round() *100/100:<b> ";
   printf("%.2f",round($number*100)/100);
   echo "</b><br />----------------";
}
?>

it looks that small numbers are not always rounded the way one expects, regardless of the rounding method used. The results are:

Number: 1.255
Printf(): 1.25
Printf() and round(): 1.25
Printf() and round() *100/100: 1.25
----------------
Number: 3.255
Printf(): 3.25
Printf() and round(): 3.25
Printf() and round() *100/100: 3.26
----------------
Number: 10.255
Printf(): 10.26
Printf() and round(): 10.26
Printf() and round() *100/100: 10.26

So to get around this I came out with a small 'fuzz'-ing:
<?php
function myFormattedRoundedNumber($number, $fuzz = 0.00000000001){
   return sprintf("%.2f", (($number>=0) ? ($number+$fuzz) : ($number-$fuzz)));
}
?>
As you can see, it also takes into account the negative numbers.
PiotrL
13-Nov-2003 09:44
There are many ways to round floating-point numbers.
And many valid (!) algorithms. This is because the algorithm depends on the domain of value and sometimes on... country.
For example as far as I know in my country money is rounded in the same way as in math calculations:

1.4 => 1
1.5 => 2
1.6 => 2
and
2.5 => 3

A lot of rounding algorithms (and very easy to implement in every language) can be found here:
 
http://www.merlyn.demon.co.uk/pas-chop.htm
26-Aug-2003 07:12
Many have thus far mentioned problems encountered when trying to add a small fuzz factor to a number such as 1.499999999.  This is the way I get around that problem using , allbeit probably less efficient than assuming a small possiblitiy for error:

$numberToRound = 1.5;

//Convert to string.
$numberToRound = "$numberToRound";

//iff number ends in a "5", add fuzz
if (eregi("$5", $pages)) $pages += .000001;   

$round = round($pages, 0);
ianring (at) golden.net
08-Aug-2003 03:30
The round() function may indeed work properly with half-values (eg. 1.5), but this little method will give you peace of mind. Add some "fuzz" to your function with a miniscule delta value.

$delta = 0.00001;
$x = round($x+$delta);

This is fine, unless $x has a value of 1.49999 ... if you worried about that, use this method instead:

if(($x-floor($x))==0.5){
   $x+=$delta;
}
$x = round($x);

you can change your "optimistic" delta into a "pessimistic" delta by subtracting instead of adding.

Cheers,
Ian Ring
ralf dot schreijer at smc dot uni-muenster dot de
18-Jun-2003 08:39
The function below regards a higher number of digits for rounding as the number of digits you want to round! At least it rounds a Value to the number of digits you want to:

function MyRound($iValue, $iDigits, $iPrecision){
   $iDigits = intval($iDigits);
   $iPrecision = intval($iPrecision);
   if($iDigits > $iPrecision){ $iPrecision = $iDigits; }
   for($i = $iPrecision; $i >= $iDigits; $i--){
     $iValue = round($iValue, $i);
   } // for($i = $iPrecision; $i >= $iDigits; $i--) -- END
   return $iValue;
}
Oromian
13-May-2003 08:08
<?
// Rounding to the nearest fifth
// or any other increment you wish...

$percent = "48";
  $num = round($percent/5)*5;
   echo $num;
   // returns 50

$percentt = "47";
  $numm = round($percentt/5)*5;
   echo $numm;
   // returns 45
?>
eb at st-us dot com
18-Jan-2003 03:16
/*next line will output 1.4999 as 1.49, no round. Use it if you want to collect fractional money less than 0.01 after for example % calculations.*/
$a=1.4999;
$a = sprintf("%01.2lf", floor($a*100)/100); //$a=1.49
tichoux at charlevoix dot net
24-Oct-2002 05:06
for a poll, if you want to have 100% and not 99 or 99.99 % you can do that :

round( number_format( (($individual_result*100)/$total_result), 2), 1)
kt at netspirit dot ch
21-Aug-2002 12:10
because of some site-effects between round() and modulo, therfore the result is not exactly at  every time ...
another way ( and without site-effects) of getting 0.05 increments for currencies, f.e. swiss francs:

$res = (round(20*$chf))/20;
echo $res;

with kind regards
php at silisoftware dot com
15-Aug-2002 05:15
Here's a function to round to an arbitary number of significant digits. Don't confuse it with rounding to a negative precision - that counts back from the decimal point, this function counts forward from the Most Significant Digit.

ex:
round(1241757, -3); // 1242000
RoundSigDigs(1241757, 3); // 1240000

Works on negative numbers too. $sigdigs should be >= 0

function RoundSigDigs($number, $sigdigs) {
   $multiplier = 1;
   while ($number < 0.1) {
       $number *= 10;
       $multiplier /= 10;
   }
   while ($number >= 1) {
       $number /= 10;
       $multiplier *= 10;
   }
   return round($number, $sigdigs) * $multiplier;
}
dalef at bendnet dot com
26-Mar-2002 03:27
for php 3.x, if you need to use the precision arg:

function round3x($val,$precision){
$exp = pow(10,$precision);
$val = $val *  $exp;
$val = round($val);
$val = $val /  $exp;
return $val;
}
js5 at sanger dot ac dot uk
18-Jan-2002 03:17
This isn't a bug. Rounding of "halves" is usally done to the even number. This means that on average half of the "halves" are rounded up and half of the "halves" are rounded down. So that
any "average" calculated should not be affected by the rounding.
felix at innovative-web dot NOSP dot AM dot de
31-Dec-2001 10:07
Hi!

Yet another update to the bcround function. Vittorio Moccia pointed out that it didn't work with "infinite" precision. However, the function below allows you to gain the precision you need. $precision specifies the number of decimals behind $decimals that shall be used for rounding (10 or 20 is a good value). Hope this was the last bug in the function. If you find any more, don't hesitate to contact me.

function bcround ($number, $decimals, $precision)
{
 $precision_add = str_repeat("5",$precision);

 if (bccomp($number,0) > 0)
 {
  return (bcadd (bcadd ($number, "0.".str_repeat("0",$decimals).$precision_add, $decimals+$precision), 0, $decimals));
 }
 else
 {
  return (bcadd (bcsub ($number, "0.".str_repeat("0",$decimals).$precision_add, $decimals+$precision), 0, $decimals));
 }
}

- Felix Schwarz, Innovative
twan at ecreation dot nl
16-May-2000 09:51
If you'd only want to round for displaying variables (not for calculating on the rounded result) then you should use printf with the float:
printf ("%6.2f",3.39532);

This returns: 3.40 .
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