round

(PHP 4, PHP 5, PHP 7, PHP 8)

round — 对浮点数进行四舍五入

说明

round(int|float $num, int $precision = 0, int $mode = PHP_ROUND_HALF_UP): float

返回将 num 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）。

参数

num

要处理的值。

precision

可选的十进制小数点后数字的数目。

如果 precision 是正数，则 num 会四舍五入到小数点后 precision 位有效数字。

如果 precision 是负数，则 num 四舍五入到小数点前 precision 位有效数字。即 pow(10, -$precision) 最接近的倍数，例如，precision 为 -1，num 可以四舍五入到十位，precision 为 -2，num 可以四舍五入到百位，等等。

mode

使用以下常量指定四舍五入发生的模式。

常量 说明
PHP_ROUND_HALF_UP 当 num 恰好处于中间时，将其向远离零的方向舍入，使 1.5 变为 2，-1.5 变为 -2。
PHP_ROUND_HALF_DOWN 当 num 恰好处于中间时，将其向靠近零的方向舍入，使 1.5 变为 1，-1.5 变为 -1。
PHP_ROUND_HALF_EVEN 将 num 四舍五入到最接近的偶数值，1.5 和 2.5 都变为 2。
PHP_ROUND_HALF_ODD 将 num 四舍五入到最接近的奇数值，1.5 变为 1，2.5 变为 3。

返回值

值是四舍五入到指定 precision 精度的 float。

更新日志

版本 说明
8.0.0 num 不再接受支持数字转换的内部对象。

示例

示例 #1 round() 示例

<?php
var_dump(round(3.4));
var_dump(round(3.5));
var_dump(round(3.6));
var_dump(round(3.6, 0));
var_dump(round(5.045, 2));
var_dump(round(5.055, 2));
var_dump(round(345, -2));
var_dump(round(345, -3));
var_dump(round(678, -2));
var_dump(round(678, -3));
?>

以上示例会输出：

float(3)
float(4)
float(4)
float(4)
float(5.05)
float(5.06)
float(300)
float(0)
float(700)
float(1000)

示例 #2 precision 如何影响 float

<?php
$number = 135.79;

var_dump(round($number, 3));
var_dump(round($number, 2));
var_dump(round($number, 1));
var_dump(round($number, 0));
var_dump(round($number, -1));
var_dump(round($number, -2));
var_dump(round($number, -3));
?>

以上示例会输出：

float(135.79)
float(135.79)
float(135.8)
float(136)
float(140)
float(100)
float(0)

示例 #3 mode 示例

<?php
echo 'Rounding modes with 9.5' . PHP_EOL;
var_dump(round(9.5, 0, PHP_ROUND_HALF_UP));
var_dump(round(9.5, 0, PHP_ROUND_HALF_DOWN));
var_dump(round(9.5, 0, PHP_ROUND_HALF_EVEN));
var_dump(round(9.5, 0, PHP_ROUND_HALF_ODD));

echo PHP_EOL;
echo 'Rounding modes with 8.5' . PHP_EOL;
var_dump(round(8.5, 0, PHP_ROUND_HALF_UP));
var_dump(round(8.5, 0, PHP_ROUND_HALF_DOWN));
var_dump(round(8.5, 0, PHP_ROUND_HALF_EVEN));
var_dump(round(8.5, 0, PHP_ROUND_HALF_ODD));
?>

以上示例会输出：

Rounding modes with 9.5
float(10)
float(9)
float(10)
float(9)

Rounding modes with 8.5
float(9)
float(8)
float(8)
float(9)

示例 #4 带 precision 的 mode 示例

<?php
echo 'Using PHP_ROUND_HALF_UP with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_UP));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_UP));

echo PHP_EOL;
echo 'Using PHP_ROUND_HALF_DOWN with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_DOWN));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_DOWN));

echo PHP_EOL;
echo 'Using PHP_ROUND_HALF_EVEN with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_EVEN));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_EVEN));

echo PHP_EOL;
echo 'Using PHP_ROUND_HALF_ODD with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_ODD));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_ODD));
?>

以上示例会输出：

Using PHP_ROUND_HALF_UP with 1 decimal digit precision
float(1.6)
float(-1.6)

Using PHP_ROUND_HALF_DOWN with 1 decimal digit precision
float(1.5)
float(-1.5)

Using PHP_ROUND_HALF_EVEN with 1 decimal digit precision
float(1.6)
float(-1.6)

Using PHP_ROUND_HALF_ODD with 1 decimal digit precision
float(1.5)
float(-1.5)

参见

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用户贡献的备注 13 notes

up
324
takingsides at gmail dot com
10 years ago
In my opinion this function lacks two flags:

- PHP_ROUND_UP - Always round up.
- PHP_ROUND_DOWN - Always round down.

In accounting, it's often necessary to always round up, or down to a precision of thousandths.

<?php
function round_up($number, $precision = 2)
{
$fig = (int) str_pad('1', $precision, '0');
return (ceil($number * $fig) / $fig);
}

function round_down($number, $precision = 2)
{
$fig = (int) str_pad('1', $precision, '0');
return (floor($number * $fig) / $fig);
}
?>
up
33
depaula at unilogica dot com
8 years ago
As PHP doesn't have a a native number truncate function, this is my solution - a function that can be usefull if you need truncate instead round a number.

<?php
/**
* Truncate a float number, example: <code>truncate(-1.49999, 2); // returns -1.49
* truncate(.49999, 3); // returns 0.499
* </code>
* @param float $val Float number to be truncate
* @param int f Number of precision
* @return float
*/
function truncate($val, $f="0")
{
if(($p = strpos($val, '.')) !== false) {
$val = floatval(substr($val, 0, $p + 1 + $f));
}
return $val;
}
?>

Originally posted in http://stackoverflow.com/a/12710283/1596489
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30
slimusgm at gmail dot com
10 years ago
If you have negative zero and you need return positive number simple add +0:

$number = -2.38419e-07;
var_dump(round($number,1));//float(-0)
var_dump(round($number,1) + 0);//float(0)
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21
djcox99 at googlemail dot com
11 years ago
I discovered that under some conditions you can get rounding errors with round when converting the number to a string afterwards.

To fix this I swapped round() for number_format().

Unfortunately i cant give an example (because the number cant be represented as a string !)

essentially I had round(0.688888889,2);

which would stay as 0.68888889 when printed as a string.

But using number_format it correctly became 0.69.
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18
esion99 at gmail dot com
10 years ago
Unexpected result or misunderstanding (php v5.5.9)

<?php

echo round(1.55, 1, PHP_ROUND_HALF_DOWN); // 1.5
echo round(1.551, 1, PHP_ROUND_HALF_DOWN); //1.6

?>
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10
craft at ckdevelop dot org
11 years ago
function mround($val, $f=2, $d=6){
return sprintf("%".$d.".".$f."f", $val);
}

echo mround(34.89999); //34.90
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19
twan at ecreation dot nl
24 years ago
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:

<?php printf ("%6.2f",3.39532); ?>

This returns: 3.40 .
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17
Anonymous
14 years ago
Here is function that rounds to a specified increment, but always up. I had to use it for price adjustment that always went up to $5 increments.

<?php
function roundUpTo($number, $increments) {
$increments = 1 / $increments;
return (ceil($number * $increments) / $increments);
}
?>
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8
christian at deligant dot net
13 years ago
this function (as all mathematical operators) takes care of the setlocale setting, resulting in some weirdness when using the result where the english math notation is expected, as the printout of the result in a width: style attribute!

<?php
$a=3/4;
echo round($a, 2); // 0.75

setlocale(LC_ALL, 'it_IT@euro', 'it_IT', 'it');
$b=3/4;
echo round($b,2); // 0,75
?>
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7
michaeldnelson dot mdn at gmail dot com
15 years ago
This function will let you round to an arbitrary non-zero number. Zero of course causes a division by zero.

<?php
function roundTo($number, $to){
return round($number/$to, 0)* $to;
}

echo roundTo(87.23, 20); //80
echo roundTo(-87.23, 20); //-80
echo roundTo(87.23, .25); //87.25
echo roundTo(.23, .25); //.25
?>
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3
greghenle at gmail dot com
8 years ago
/**
* Round to first significant digit
* +N to +infinity
* -N to -infinity
*
*/
function round1stSignificant ( $N ) {
if ( $N === 0 ) {
return 0;
}

$x = floor ( log10 ( abs( $N ) ) );

return ( $N > 0 )
? ceil( $N * pow ( 10, $x * -1 ) ) * pow( 10, $x )
: floor( $N * pow ( 10, $x * -1 ) ) * pow( 10, $x );
}

echo round1stSignificant( 39144818 ) . PHP_EOL;
echo round1stSignificant( 124818 ) . PHP_EOL;
echo round1stSignificant( 0.07468 ) . PHP_EOL;
echo round1stSignificant( 0 ) . PHP_EOL;
echo round1stSignificant( -0.07468 ) . PHP_EOL;

/**
* Output
*
* 40000000
* 200000
* 0.08
* 0
* -0.08
*
*/
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9
php at silisoftware dot com
22 years ago
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:

<?php
round(1241757, -3); // 1242000
RoundSigDigs(1241757, 3); // 1240000
?>

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

<?php
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;
}
?>
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3
dastra
12 years ago
round() will sometimes return E notation when rounding a float when the amount is small enough - see https://bugs.php.net/bug.php?id=44223 . Apparently it's a feature.

To work around this "feature" when converting to a string, surround your round statement with an sprintf:

sprintf("%.10f", round( $amountToBeRounded, 10));
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