Convert u256 to string

Sway
1

How to convert u256 to string in sway?

1 Like
2

Hi @lokesh-lync ,

These docs may be useful for you:

3

hey @nick I am trying to concat a string and s u256. I was trying to do this: Convert u64 to String for concatenation - #2 by Serafim

This is the relevent code that I wrote:

pub fn concat_str_with_num(s: String, num: u256) -> String {
    let mut result = Bytes::new();
    push_bytes(result, s.as_bytes());
    push_bytes(result, String::from_ascii_str("/").as_bytes()); // an arbitrary delimeter
    push_bytes(result, convert_num_to_ascii_bytes(num));
    String::from_ascii(result)
}

fn convert_num_to_ascii_bytes(num: u256) -> Bytes {
    let mut bytes = Bytes::new();
    let mut n = num;
    if n == 0 {
        bytes.push(48);
        return bytes;
    }
    while n != 0 {
        // 48 - is an ASCII offset for digits
        bytes.push(((n % 10) + 48).try_as_u8().unwrap());
        n /= 10;
    }
    let mut reversed_bytes = Bytes::with_capacity(bytes.len());
    while !bytes.is_empty() {
        reversed_bytes.push(bytes.pop().unwrap());
    }
    return reversed_bytes;
}

fn push_bytes(ref mut a: Bytes, b: Bytes) {
    let mut i = 0;
    while i < b.len() {
        a.push(b.get(i).unwrap());
        i = i + 1;
    }
}

I am getting this error:

    |
188 |
189 |         // 48 - is an ASCII offset for digits
190 |         bytes.push(((n % 10) + 48).try_as_u8().unwrap());
    |                                    ^^^^^^^^^ No method named "try_as_u8" found for type "u256".
191 |         n /= 10;
192 |     }
    |
____

Is there some import that I am missing?

Here are my imports:

use std::primitive_conversions::u256::*;
use sway_libs::{
       ownership::{
        _owner,
        initialize_ownership,
        only_owner,
    },
    asset::metadata::*,
    reentrancy::*
};

use standards::{
    src5::{SRC5, State, AccessError},
    src20::SRC20,
    src7::{SRC7, Metadata}
};

use std::{
    asset::{
        burn,
        mint_to,
        transfer,
    },
    call_frames::{
        msg_asset_id,
    },
    constants::DEFAULT_SUB_ID,
    context::msg_amount,
    string::String,
    hash::Hash,
    storage::storage_map::StorageMap,
    storage::storage_string::StorageString,
    bytes::*
};
1 Like
4

By the looks of your code @lokesh-lync you are trying to convert a u256 number into a u8, this downcasting is not possible or likely not what you want (as you would lose 248 bits of precision here on the number).

The u256 primitive only has a as_b256 conversion:

Do you want this number to be a u256 ((n % 10) + 48)?

Or is this suppose to be a single byte/u8? If so, you should instantiate this as a single u8 then add it to the bytes array.

2 Likes
5

what I am trying to do is something similar to this: Convert u64 to String for concatenation - #2 by Serafim

I am using the same code, the difference is that this guy is converting u64 to String and I am trying to convert u256 to String. Wouldn’t he loose some bits of precision as well? But it seems to be working there. So, I am not sure why is it not working for u256

6

HI @lokesh-lync ,

If you want to convert a u256 to a string I’d do the following:

  1. convert the u256 to a b256
    u256 in core - Sway
  2. convert the b256 to a bytes
    Sway | Fuel Docs
  3. convert the bytes to a String type String in string - Sway
7

ok i’ll give this a try and let you know. Thanks!

1 Like
8

hey @calldelegation you suggested me to do something similar earlier here: Problems with signature verification on chain

can you also look into this and suggest me where I am going wrong?

9

UPDATE: I was able to make u64 work. u256 does not have some methods that I wanted to use. I am going with u64 for now.