I'm doing oraclize calls on the json rpc of a chain to get this function:

  function getTransfer(uint _transferId) public view returns(uint,address,uint){
    Details memory _locked = transferDetails[_transferId];

It's really not that important what it does, but when I call this function from oraclize, I get back a string with all three variables...for instance:


I'm working on a callback to parse this into a uint, an address, and a uint. This is what I have so far:

function __callback(string result) public returns(uint,address,uint){
    emit Print(result);
    string memory _int = Strings.substring(result,60,90);
    emit Print(_int);
    emit P2(stringToUint(_int));
    uint _amount= parseInt(_int);
    _int =strConcat('0x',Strings.substring(result,91,130)) ;
    address _owner =  parseAddr(_int);
    _int =Strings.substring(result,131,194) ;
    uint _transId = parseInt(_int);
    return (_amount,_transId,_transId);

This sort of works, but the problem is that the uint's are actually in hex value (this string should return .8e18,0x,1), but I need to convert a literal string to a hex to a decimal..if you have any ideas. Also, can I use substring, or will the length of my string change with the values?

The code of the contract we're calling is here: https://ropsten.etherscan.io/address/0xd29d27cfacf7b77a16edac7c2cddf07dc4a603b8#readContract

p.s. It can break remix doing this kind of string manipulation

1 Answer 1


This code works if anyone else is curious..had to write a string uint hex to uint converters:

  pragma solidity ^0.4.21;

 * Set of utilities to parse results of JSON-RPC call from oraclize.
contract HexUtils {

    //constants for comparison and conversions below
    byte constant a = byte('a');
    byte constant f = byte('f');
    byte constant A = byte('A');
    byte constant F = byte('F');
    byte constant zero = byte('0');
    byte constant nine = byte('9');

     * Convert a character to its hex value as a byte. This is NOT
     * very efficient but is a brute-force way of getting the job done.
     * It's possible to optimize this with assembly in solidity but
     * that would require a lot more time.
    function hexCharToByte(uint c) pure internal returns(uint) {
        byte b = byte(c);

        //convert ascii char to hex value
        if(b >= zero && b <= nine) {
            return c - uint(zero);
        } else if(b >= a && b <= f) {
            return 10 + (c - uint(a));
        } else if(b >= A && b <= F) {
            return 10 + (c - uint(A));

     * Check whether a string has hex prefix.
    function hasZeroXPrefix(string s) pure internal returns(bool) {
        bytes memory b = bytes(s);
        if(b.length < 2) {
            return false;
        return b[1] == 'x';

     * Convert a hex string to a uint. This is NOT very efficient but
     * gets the job done. Could probably optimize with assembly but would
     * require a lot more time.
    function hexToUint(string s) pure public returns(uint) {
        //convert string to bytes
        bytes memory b = bytes(s);

        //make sure zero-padded
        require(b.length % 2 == 0, "String must have an even number of characters");

        //starting index to parse from
        uint i = 0;
        //strip 0x if present
        if(hasZeroXPrefix(s)) {
            i = 2;
        uint r = 0;
        for(;i<b.length;i++) {
            //convert each ascii char in string to its hex/byte value.
            uint b1 = hexCharToByte(uint(b[i]));

            //shift over a nibble for each char since hex has 2 chars per byte
            //OR the result to fill in lower 4 bits with hex byte value.
            r = (r << 4) | b1;
        //result is hex-shifted value of all bytes in input string.
        return r;

     * Extract a substring from an input string.
    function substr(string s, uint start, uint end) pure public returns(string) {
        require(end > start, "End must be more than start");
        bytes memory res = new bytes(end-start);
        bytes memory bts = bytes(s);
        require(end <= bts.length, "End must be less than or equal to the length of string");
        require(start >= 0 && start < bts.length, "Start must be between 0 and length of string");

        uint idx = 0;
        for(uint i=start;i<end;++i) {
          //just copy bytes over
            res[idx] = bts[i];
        return string(res);

     * Parse a hex string into an address.
    function parseAddr(string _a) internal pure returns (address){
        //address is really a uint160...
        uint iaddr = hexToUint(_a);
        return address(iaddr);

     * Parse oraclize result into uint, address, uint values.
    function parseResults(string _hexData) pure public returns(uint, address, uint) {
        //start at zero or 2 depending on 0x prefix in string
        uint startIdx = 0;
        if(hasZeroXPrefix(_hexData)) {
            startIdx = 2;
        bytes memory bts = bytes(_hexData);
        //take the first 64 bytes and convert to uint
        uint ethVal = hexToUint(substr(_hexData, startIdx,64+startIdx));

        //id is at the end and will be 64 bytes. So grab its starting idx first.
        uint idStart = bts.length - 64;

        //the address portion will end where the id starts.
        uint addrEnd = idStart-1;

        //parse the last 40 bytes of the address hex.
        address addr = parseAddr(substr(_hexData, addrEnd-40, addrEnd));

        //then extract the id
        uint id = hexToUint(substr(_hexData, idStart, bts.length));

        return (ethVal, addr, id);

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