PHP gives incorrect results when formatting long numbers

问题

I am working with huge numbers for website purposes and I need long calculation. When I echo a long number I don't get the correct output.

Example

// A random number
$x = 100000000000000000000000000;

$x = number_format($x);
echo "The number is: $x <br>";
// Result: 100,000,000,000,000,004,764,729,344 
// I'm not getting the value assigned to $x

回答1:

Your number is actually too big for php standard integers. php uses 64 bit integers which can hold values within range -9223372036854775808 (PHP_INT_MIN) to +9223372036854775807 (PHP_INT_MAX).

Your number is about 87 bits long which simply is too much.

If you really need such big numbers you should use the php BC math types, explained in the manual: http://php.net/manual/en/ref.bc.php

If you just want to format a string formed like a huge number then use something like this:

function number_format_string($number) {
    return strrev(implode(',', str_split(strrev($number), 3)));
}

$x = '100000000000000000000000000';

$x = number_format_string($x);
echo "The number is: $x\n";

// Output: The number is: 100,000,000,000,000,000,000,000,000

Edit: Added strrev() to function because the string needs to be reversed before splitting it up (thanks to @ceeee for the hint). This ensures that the delimiter is placed at right position when length of input is not divisible by 3. Generated string needs to be reversed afterwards again.

Working example can be found at http://sandbox.onlinephpfunctions.com/code/c10fc9b9e2c65a27710fb6be3a0202ad492e3e9a

回答2:

answer @maxhb has bug. if the input is '10000000000000000000000' the out put would be:

The number is: 100,000,000,000,000,000,000,00

Which is incorrect. So try below code:

function number_format_string($number, $delimeter = ',')
{
    return strrev(implode($delimeter, str_split(strrev($number), 3)));
}

$x = '10000000000000000000000';

$x = number_format_string($x);
echo "The number is: $x\n";

// Output: The number is: 10,000,000,000,000,000,000,000

回答3:

The largest integer that can be represented in a 64bit PHP install, compared to your number:

   9,223,372,036,854,775,808 - largest possible signed 64bit integer
   100000000000000000000000000 - your number

since you're exceeding the maximum number size, you can't expect to get useful results without using something like gmp/bcmath.

回答4:

http://php.net/manual/en/function.number-format.php

That is the solution:

<?php

#    Output easy-to-read numbers
#    by james at bandit.co.nz
function bd_nice_number($n) {
    // first strip any formatting;
    $n = (0+str_replace(",","",$n));
    // is this a number?
    if(!is_numeric($n)) return false;
    // now filter it;
    if($n>1000000000000) return round(($n/1000000000000),1).' trillion';
    else if($n>1000000000) return round(($n/1000000000),1).' billion';
    else if($n>1000000) return round(($n/1000000),1).' million';
    else if($n>1000) return round(($n/1000),1).' thousand';

    return number_format($n);
    }
?>

来源：https://stackoverflow.com/questions/35169951/php-gives-incorrect-results-when-formatting-long-numbers

标签

php

integer

number-formatting

biginteger

arbitrary-precision