6

Hey is there a way to convert bytes to uint in Solidity?

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  • Could you explain what conversion you would like? Best if you can give an example of a bytes value and the corresponding uint value you would like to see. – user19510 Jun 14 '18 at 14:52
4

You can use this function to convert bytes to unit:

pragma solidity ^0.4.23;

contract mycontract {

    function bytesToUint(bytes b) public returns (uint256){
        uint256 number;
        for(uint i=0;i<b.length;i++){
            number = number + uint(b[i])*(2**(8*(b.length-(i+1))));
        }
        return number;
    }
}

The amount of gas used depends on the length of your bytes variable, but this is cheap. Converting a bytes variable of length 20 uses about 420 gas.

Hope this helps

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  • Getting an error in Remix: TypeError: Return argument type bytes memory is not implicitly convertible to expected type uint256 – arete Jun 14 '18 at 15:02
  • Can you show me your code?, this works for me well in remix, I put the whole code so you can just copy and paste it. Let me know – Jaime Jun 14 '18 at 15:13
  • Oh there you go. I think your first post had the return value as "b". This works. Thanks! – arete Jun 14 '18 at 15:25
  • Good, if this answers your question, please accept it. – Jaime Jun 14 '18 at 15:31
1

Slicing an uint out of bytes using inline assembly

function sliceUint(bytes bs, uint start)
    internal pure
    returns (uint)
{
    require(bs.length >= start + 32, "slicing out of range");
    uint x;
    assembly {
        x := mload(add(bs, add(0x20, start)))
    }
    return x;
}
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1

The fully working modern solution from Consensys dude can be found here:

https://github.com/GNSPS/solidity-bytes-utils/blob/master/contracts/BytesLib.sol

The accepted answer's code is not compiling in Solidity >0.5; with implicit type conversion error.

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