Solidity: Conversion bytes memory to uint

Question

Is there a workaround to convert a bytes memory to uint256?

Duplicate of https://ethereum.stackexchange.com/questions/41944/hexadecimal-bytes-to-binary-uint-in-a-smart-contract — Alex G.P., May 22 '18 at 15:35
Actually is not the same question, since bytes is a dynamically-sized byte array, while bytes8 is not. — bordalix, May 22 '18 at 15:49
Indeed trying to do the same of ethereum.stackexchange.com/questions/41944/ we have the following compiler error: " TypeError: Explicit type conversion not allowed from "bytes memory" to "uint256" — Stefano Angieri, May 22 '18 at 15:53

score 9 · Accepted Answer · answered Jul 15 '18 at 14:40

9

It's possible but there's no easy way to do it. You either have to do some bitwise xor and shifting to build the uint, or use inline assembly to mload.

Here's the working code, feel free to copy paste

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;
}

answered Jul 15 '18 at 14:40

libertylocked

1,368
8
16

This should be the accepted answer. Works great, thanks @libertylocked – The Nomad Jul 30 '18 at 06:18

score 0 · Answer 2 · answered May 22 '18 at 15:52

0

You cannot cast bytes to uint256, since bytes is a dynamically-sized byte array.

If you really need to do this conversion, use bytes32 (or any other fixed sized byte array) instead of bytes and then convert it to uint256 by a simple cast:

function two(bytes32 inBytes) pure public returns (uint256 outUint) {
      return uint256(inBytes);
}

answered May 22 '18 at 15:52

bordalix

918
7
11

The problem is that I need to work with dynamically-sized byte array.
Another question: Is not possible to cast dynamically-sized byte array to fixed sized byte array?
– Stefano Angieri May 22 '18 at 16:09
Think about this: how can you to convert a dynamically-sized array thats bigger then a fixed sized array? It won't fit ;) – bordalix May 23 '18 at 14:07
this doesn't work in solc 0.5.x, any idea how to convert fixed size byte arrays to and from uint? – okwme Sep 22 '19 at 15:09

score 0 · Answer 3 · answered May 22 '18 at 16:35

0

Is possible to simply cast bytes memory to string and then use the stringToUint function I found in the Answer: How to convert string to int.

answered May 22 '18 at 16:35

Stefano Angieri

153
1
7

Solidity: Conversion bytes memory to uint

3 Answers3

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