type cast exponential number to int or float

问题

The following code:

echo (int) "2e2";
echo (int) 2e2;
echo (float) "2e2";

outputs

2
200
200

.. and i have no idea why. Thanks.

回答1:

"2e2" is scientific notation, meaning 2*10² == 200.

1. In your first example, parsing the string as an int reads only digits up to the first non-digit (so it ignores the e).
2. The PHP parser treats 2e2 as a float literal with value 200.0 and this gives 200 when cast to a int.
3. Parsing the string as a float understands the notation and gives the expected result of 200.

来源：https://stackoverflow.com/questions/8090275/type-cast-exponential-number-to-int-or-float