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

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 2

As of feb 2021 you can do

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

Answer 3

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 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

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 7

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 8

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 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

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);
}

Answer 11

    // 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 12

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. 😊😊😊