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| -rw-r--r-- | docs/frequently-asked-questions.rst | 14 |
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diff --git a/docs/frequently-asked-questions.rst b/docs/frequently-asked-questions.rst index 94491381..fd68aa11 100644 --- a/docs/frequently-asked-questions.rst +++ b/docs/frequently-asked-questions.rst @@ -742,6 +742,20 @@ If you want to send 20 Ether from a contract to the address `x`, you use `x.send Here, `x` can be a plain address or a contract. If the contract already explicitly defines a function `send` (and thus overwrites the special function), you can use `address(x).send(20 ether);`. +What does the following strange check do in the Custom Token contract? +====================================================================== + +:: + + if (balanceOf[_to] + _value < balanceOf[_to]) throw; + +Integers in Solidity (and most other machine-related programming languages) are restricted to a certain range. +For `uint256`, this is `0` up to `2**256 - 1`. If the result of some operation on those numbers +does not fit inside this range, it is truncated. These truncations can have +`serious consequences <https://en.bitcoin.it/wiki/Value_overflow_incident>`_, so code like the one +above is necessary to avoid certain attacks. + + More Questions? =============== |