php calculation gives a weird result for 1500000-20%

问题

May be I might be blind or silly, but look at my function:

function max_min_twenty($value) {
if ((int)$value == 0) {
    return "0"; 
} else {
    $percent_val = ((int)$value / 100) * 20;
    $maxvalue = (int)$value + $percent_val;
    $minvalue = (int)$value - $percent_val;
    $returnvalue = round($minvalue)."-".round($maxvalue);
    return $returnvalue;
}
}

Seems that this is really easy! It works like it should, but if my $value is 1500000 it gives me back 1,2E+6 for $minvalue - It does well if I choose a different number or if I change the percent to 19 or 21. Whats that?

Its running on PHP Version 5.2.4-2ubuntu5.27

回答1:

Format the number explicitly as an integer? round returns a float and so I believe the default formatting is "getting confused" or "hitting an edge case" and reverts to displaying scientific notation. (I can't trigger the problem on ideone - it might be specific to a particular PHP version/environment - but the symptoms fit.)

Try sprintf:

return sprintf("%d-%d", $minvalue, $maxvalue);

(I removed round as the %d forces the arguments to be treated as integers; however, there might be subtle differences in the rounding rules .. I don't know.)

回答2:

try to use number_format

function max_min_twenty($value) {
if ((int)$value == 0) {
    return "0"; 
} else {
    $percent_val = ((int)$value / 100) * 20;
    $maxvalue = (int)$value + $percent_val;
    $minvalue = (int)$value - $percent_val;
    $returnvalue = number_format(round($minvalue),"0","-","")."-   ".number_format(round($maxvalue),"0","-","");
    echo $returnvalue;
}
}

it changed scientific notation to standard form.

回答3:

You are seeing a bugged behavior in older versions of PHP. This was bug #43053 that was resolved in PHP 5.3.0.

Take, for example, this code:

for ($i = 1000000; $i < 2000000; $i += 100000)
    echo round($i) . "--\n";

On PHP 5.2.6 and lower, it produces the following (sample; can't guarantee CodePad will always be on old PHP):

1000000--
1100000--
1.2E+6--
1300000--
1.4E+6--
1500000--
1600000--
1.7E+6--
1800000--
1.9E+6--

On PHP 5.3.0 and up, though, the correct behavior can be seen:

1000000--
1100000--
1200000--
1300000--
1400000--
1500000--
1600000--
1700000--
1800000--
1900000--

This can be fixed by upgrading PHP or by avoiding round(), as @user2246674 suggests in his answer.

来源：https://stackoverflow.com/questions/17119955/php-calculation-gives-a-weird-result-for-1500000-20

标签

php

percentage

subtraction