[Ethereum] How to check if a bytes32 represents an empty string

bytes-x(1~32) can store a string, if the length of string is greater than x, then the part out of length will be dropped. It's a simple test contract

pragma solidity ^0.4.13;

contract Bytes32Test {

    bytes32 msg;

    function add(bytes32 _msg){
        msg = _msg;
    }

    function show() constant returns (bytes32){
        return msg;
    }

}

and i invoke add function by a param 'some string over 32 characters in length that can seem to be up to 128 characters in length to be stored in bytes32', and now we call show function, the result is

0x736f6d6520737472696e67206f76657220333220636861726163746572732069

the result is "some string over 32 characters i" if we convert it from hex to ascii.

> web3.toAscii("0x736f6d6520737472696e67206f76657220333220636861726163746572732069")
"some string over 32 characters i"

Hope it helps~

Your issue is here:

uint result = 0;

The uint type can hold up to 2^256 - 1. In decimal, this is

115792089237316195423570985008687907853269984665640564039457584007913129639935

Note that this is less than double the result you get, which confirms that you've reached the 256 bit limit:

 79381376136047024986163664703589883750854290615248988403587492614211165487105

Your test number is actually 273 bits wide.

If you need to handle integers larger than 256 bits then you're going to have to define some sort of bigInteger type to handle them. I'm not aware of a generic bigInt library for Solidity; you may need to roll your own.