PHP round（）返回意外值

Question

I have a double value of 2.6647 which I am trying to round mathematically correct to 2 decimal places.

I am expecting a return value of 2.67.

7 (the last decimal place) should round 4 (the second-last decimal place) up to 5, 5 should round 6 (the third-last decimal place) up to 7.

$value = 2.6647;
echo round( $value, 2, PHP_ROUND_HALF_UP );

But instead I receive 2.66. Why is this happening?

PHP Version is 5.3.28.

Answer 1

Rounding to n decimals is driven by n+1th decimal. In this case the third one decimal is 4, so the number is rounded down to 2.66.