Strange number conversion error in PHP

How come the result for

intval("19.90"*100)

is

1989

and not 1990 as one would ex开发者_如何学编程pect (PHP 5.2.14)?

That's because 19.90 is not exactly representable in base 2 and the closest approximation is slightly lower than 19.90.

Namely, this closest approximation is exactly 2^-48 × 0x13E66666666666. You can see its exact value in decimal form here, if you're interested.

This rounding error is propagated when you multiply by 100. intval will force a cast of the float to an integer, and such casts always rounds towards 0, which is why you see 1989. Use round instead.

You can also use bc* function for working with float :

$var = bcmul("19.90", "100");
echo intval($var);

intval converts doubles to integers by truncating the fractional component of the number. When dealing with some values, this can give odd results. Consider the following:

print intval ((0.1 + 0.7) * 10);

This will most likely print out 7, instead of the expected value of 8.

For more information, see the section on floating point numbers in the PHP manual

Why are you using intval on a floating point number? I agree with you that the output is a little off but it has to do with the relative inprecision of floating point numbers.

Why not just use floatval("19.90"*100) which outputs 1990

I believe the php doc at http://de2.php.net/manual/en/function.intval.php is omitting the fact that intval will not deliver "the integer value" but the integer (that is non-fractional) part of the number. It does not round.