How to convert a bytes32 to string

Question

How can I convert a bytes32 to a string? Does anyone has a magic function or library which does it?

Answer 1

As of feb 2021 you can do

bytes32 foo = "hello";
string memory bar = string(abi.encodePacked(foo));

Answer 2

Here's one:

function bytes32ToString(bytes32 x) constant returns (string) {
    bytes memory bytesString = new bytes(32);
    uint charCount = 0;
    for (uint j = 0; j < 32; j++) {
        byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
        if (char != 0) {
            bytesString[charCount] = char;
            charCount++;
        }
    }
    bytes memory bytesStringTrimmed = new bytes(charCount);
    for (j = 0; j < charCount; j++) {
        bytesStringTrimmed[j] = bytesString[j];
    }
    return string(bytesStringTrimmed);
}

To test, here it is combined with how to concatenate an array of bytes32. Paste the following in Remix.

contract C {
    function bytes32ToString(bytes32 x) constant returns (string) {
        bytes memory bytesString = new bytes(32);
        uint charCount = 0;
        for (uint j = 0; j < 32; j++) {
            byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
            if (char != 0) {
                bytesString[charCount] = char;
                charCount++;
            }
        }
        bytes memory bytesStringTrimmed = new bytes(charCount);
        for (j = 0; j < charCount; j++) {
            bytesStringTrimmed[j] = bytesString[j];
        }
        return string(bytesStringTrimmed);
    }

    function bytes32ArrayToString(bytes32[] data) returns (string) {
        bytes memory bytesString = new bytes(data.length * 32);
        uint urlLength;
        for (uint i=0; i<data.length; i++) {
            for (uint j=0; j<32; j++) {
                byte char = byte(bytes32(uint(data[i]) * 2 ** (8 * j)));
                if (char != 0) {
                    bytesString[urlLength] = char;
                    urlLength += 1;
                }
            }
        }
        bytes memory bytesStringTrimmed = new bytes(urlLength);
        for (i=0; i<urlLength; i++) {
            bytesStringTrimmed[i] = bytesString[i];
        }
        return string(bytesStringTrimmed);
    }    
}

Click "Create". Then in bytes32ToString field enter "0x0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef" and click bytes32ToString.

In bytes32ArrayToString field enter ["0x0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"] and click bytes32ArrayToString.

Both will show same result (ABI encoding): Result: "0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000200123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"

---

Here's another example. In bytes32ToString field enter "0xc3b6" and click bytes32ToString. You will get ö.

Answer 3

Based on the latest compiler version 0.4.24, I use the following.

function convertingToString()public returns(string){
bytes32 memory hw = "Hello World";
string memory converted = string(hw);
return converted;
}

Using explicit conversion to carry it out. The reverse is also possible.

For versions 0.5.0+ please use (tested from 0.5 to 0.7.2 - it is likely that it will continue to work past 0.7.2):

function bytes32ToString(bytes32 _bytes32) public pure returns (string memory) {
        uint8 i = 0;
        while(i < 32 && _bytes32[i] != 0) {
            i++;
        }
        bytes memory bytesArray = new bytes(i);
        for (i = 0; i < 32 && _bytes32[i] != 0; i++) {
            bytesArray[i] = _bytes32[i];
        }
        return string(bytesArray);
    }

Answer 4

How to convert a bytes32 to string:

pragma solidity ^0.4.15;

contract Bytes32ToString {

function bytes32ToStr(bytes32 _bytes32) public pure returns (string) {

    // string memory str = string(_bytes32);
    // TypeError: Explicit type conversion not allowed from "bytes32" to "string storage pointer"
    // thus we should fist convert bytes32 to bytes (to dynamically-sized byte array)

    bytes memory bytesArray = new bytes(32);
    for (uint256 i; i < 32; i++) {
        bytesArray[i] = _bytes32[i];
        }
    return string(bytesArray);
    }

}

Answer 5

It's recommended you convert a bytes32 to a string using Web3.js to avoid gas costs. To do this, you would get the value of the bytes32 from Solidity to the front end then do:

web3.utils.hexToString(bytes32);

This will convert the bytes32 to a string that you can then see and use in your frontend dApp.

Answer 6

Like @e18r already mentioned, the simplest way to do it without having to write all these crazy functions like everyone else is answering with (and would cost more gas), just do:

string(abi.encodePacked(bytes32));

Answer 7

Just in case, if you want to convert bytes32 to ASCII string, you can use the OpenZeppelin Strings library.

https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2504

Strings.toHexString(uint256(tokenIdSeed), 32),

The output should be like

0xd8df8ecd5432b247d2fc2beb0619d637e9de0df7512bd36220582deda9a1df6e 

(this is just covert hexadecimal value of the bytes32 to string)

Answer 8

In version 0.5.0 and above i ended up with using Viktor answer How to convert a bytes32 to string but removing the zeros otherwise you will end up with

'ERC20\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000'

instead of

'ERC20'

This is the code:

/* bytes32 (fixed-size array) to string (dynamically-sized array) */
function bytes32ToString(bytes32 _bytes32) public pure returns (string memory) {
        uint8 i = 0;
        while(i < 32 && _bytes32[i] != 0) {
            i++;
        }
        bytes memory bytesArray = new bytes(i);
        for (i = 0; i < 32 && _bytes32[i] != 0; i++) {
            bytesArray[i] = _bytes32[i];
        }
        return string(bytesArray);
    }

Answer 9

A more gas-efficient method based on this answer (For versions 0.5.0+):

function toString(bytes32 source)
    internal
    pure
    returns (string memory result)
{
    uint8 length = 0;
    while (source[length] != 0 && length < 32) {
        length++;
    }
    assembly {
        result := mload(0x40)
        // new "memory end" including padding (the string isn't larger than 32 bytes)
        mstore(0x40, add(result, 0x40))
        // store length in memory
        mstore(result, length)
        // write actual data
        mstore(add(result, 0x20), source)
    }
}

This solution is using assembly to copy data to memory instead of for looping.

Answer 10

    // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.7;
    contract stringtobytes{
        function set(string memory  _a)public pure returns(bytes memory){
            return bytes(_a);
        } 
         function set1(bytes memory  _a)public pure returns(string  memory){
            return string(_a);
        } 

}

// you can convert strings to bytes(in decimal format) and vice versa with below code

//1- bytes1=8bit=2decimal

//2 bytes2=16bit=4decimal

//3 bytes3=24bit=6decimal

//4 bytes=dynamic array and reference value

Answer 11

Here's the simplest way i tried

contract ModifyString{
bytes32 public VoterName;

mapping (address => VoterStruct) public voterCalls;

struct VoterStruct{
   address VoterAddress;
   string VoterID;
   bytes32 VoterName2;
}

function addVoter(string memory _VoterID, string memory _VoterName)public {
   // Load Voter struct trough mapping
   VoterStruct storage newVoter = voterCalls[msg.sender];

   // If want to write to global variable
   VoterName = bytes32(abi.encodePacked( _VoterName));

   // If want to write to struct
   newVoter.VoterAddress = msg.sender;
   newVoter.VoterID = _VoterID;
   newVoter.VoterName2 = bytes32(abi.encodePacked(_VoterName));
}

function getVoterName() public view returns (string memory) {

   // To load from Global Variables
   bytes memory bytesData = abi.encodePacked(VoterName);

   return string(abi.encodePacked(VoterName));
}

function getVoterName2() public view returns (string memory) {

   // To look Voter name in global variable
   bytes memory bytesData = abi.encodePacked(VoterName);

   return string(abi.encodePacked(bytesData));
}

function getVoterName3() public view returns (string memory) {

   // To look Voter name in struct
   VoterStruct storage voterCall = voterCalls[msg.sender];

   return string(abi.encodePacked(voterCall.VoterName2));
}

}

so to load the string, it need to be loaded in memory, as far as i know, string = bytes (without specific bytes number)

then return the output value using

string(abi.encodePacked(bytesData))
^^^^                      ^^^^^
//The converted type to   //Loaded Variable into memory or storage

ahh so there is to: 1.1 Write String to bytes32 to Global Variable, 1.2 Load string from bytes32 from Gobal Variable, 2.1 Write String to bytes32 to Struct, 2.2 Load String to bytes32 to struct.

Answer 12

Here's how I'm doing it:

function char(byte b) returns (byte c) {
    if (b < 10) return byte(uint8(b) + 0x30);
    else return byte(uint8(b) + 0x57);
}


function bytes32string(bytes32 b32) returns (string out) {
    bytes memory s = new bytes(64);

    for (var i = 0; i < 32; i++) {
        byte b = byte(b32[i]);
        byte hi = byte(uint8(b) / 16);
        byte lo = byte(uint8(b) - 16 * uint8(hi));
        s[i*2] = char(hi);
        s[i*2+1] = char(lo);            
    }

    out = string(s);
}