is it possible to pass an integer (in this case 141) represented by the variable z from a certain restfullAPI into the custom token function: balances[msg.sender]? So in the end I want to have my own Token with 14.1 UGAu (the value from the variable z). For this purpose I use oraclize, https://remix.ethereum.org and metamask.

My smartcontract look like this:

pragma solidity ^0.4.4;

contract Token {

/// @return total amount of tokens
function totalSupply() constant returns (uint256 supply) {}

/// @param _owner The address from which the balance will be retrieved
/// @return The balance
function balanceOf(address _owner) constant returns (uint256 balance) {}

/// @notice send `_value` token to `_to` from `msg.sender`
/// @param _to The address of the recipient
/// @param _value The amount of token to be transferred
/// @return Whether the transfer was successful or not
function transfer(address _to, uint256 _value) returns (bool success) {}

/// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
/// @param _from The address of the sender
/// @param _to The address of the recipient
/// @param _value The amount of token to be transferred
/// @return Whether the transfer was successful or not
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {}

/// @notice `msg.sender` approves `_addr` to spend `_value` tokens
/// @param _spender The address of the account able to transfer the tokens
/// @param _value The amount of wei to be approved for transfer
/// @return Whether the approval was successful or not
function approve(address _spender, uint256 _value) returns (bool success) {}

/// @param _owner The address of the account owning tokens
/// @param _spender The address of the account able to transfer the tokens
/// @return Amount of remaining tokens allowed to spent
function allowance(address _owner, address _spender) constant returns (uint256 remaining) {}

event Transfer(address indexed _from, address indexed _to, uint256 _value);
event Approval(address indexed _owner, address indexed _spender, uint256 _value);


contract StandardToken is Token {

function transfer(address _to, uint256 _value) returns (bool success) {
    //Default assumes totalSupply can't be over max (2^256 - 1).
    //If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
    //Replace the if with this one instead.
    //if (balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
    if (balances[msg.sender] >= _value && _value > 0) {
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        Transfer(msg.sender, _to, _value);
        return true;
    } else { return false; }

function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
    //same as above. Replace this line with the following if you want to protect against wrapping uints.
    //if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
    if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
        balances[_to] += _value;
        balances[_from] -= _value;
        allowed[_from][msg.sender] -= _value;
        Transfer(_from, _to, _value);
        return true;
    } else { return false; }

function balanceOf(address _owner) constant returns (uint256 balance) {
    return balances[_owner];

function approve(address _spender, uint256 _value) returns (bool success) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;

function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
  return allowed[_owner][_spender];

mapping (address => uint256) balances;
mapping (address => mapping (address => uint256)) allowed;
uint256 public totalSupply;


import "./oraclize.sol"; contract UrbangoldToken is StandardToken, usingOraclize { // CHANGE THIS. Update the contract name.

/* Public variables of the token */

The following variables are OPTIONAL vanities. One does not have to include them.
They allow one to customise the token contract & in no way influences the core functionality.
Some wallets/interfaces might not even bother to look at this information.
uint256 public z;
event newOraclizeQuery(string description);
string public name;                   // Token Name
uint8 public decimals;                // How many decimals to show. To be standard complicant keep it 18
string public symbol;                 // An identifier: eg SBX, XPR etc..
string public version = 'H1.0'; 
uint256 public unitsOneEthCanBuy;     // How many units of your coin can be bought by 1 ETH?
uint256 public totalEthInWei;         // WEI is the smallest unit of ETH (the equivalent of cent in USD or satoshi in BTC). We'll store the total ETH raised via our ICO here.  
address public fundsWallet;           // Where should the raised ETH go?

// This is a constructor function 
// which means the following function name has to match the contract name declared above
function UrbangoldToken() {
    balances[msg.sender] = z;               // Give the creator all initial tokens. This is set to 1000 for example. If you want your initial tokens to be X and your decimal is 5, set this value to X * 100000. (CHANGE THIS)
    totalSupply = 1000;                        // Update total supply (1000 for example) (CHANGE THIS)
    name = "UrbangoldToken";                                   // Set the name for display purposes (CHANGE THIS)
    decimals = 1;                                               // Amount of decimals for display purposes (CHANGE THIS)
    symbol = "UGAu";                                             // Set the symbol for display purposes (CHANGE THIS)
    unitsOneEthCanBuy = 10;                                      // Set the price of your token for the ICO (CHANGE THIS)
    fundsWallet = msg.sender;     

function __callback(bytes32 myid, string result) {
    if (msg.sender != oraclize_cbAddress()) throw;
    z = parseInt(result);

function update() payable {
    newOraclizeQuery("Oraclize query was sent, standing by for the answer..");
    oraclize_query("URL", "json(https://urbangold.localtunnel.me).z");

function() payable{
    totalEthInWei = totalEthInWei + msg.value;
    uint256 amount = msg.value * unitsOneEthCanBuy;
    require(balances[fundsWallet] >= amount);

    balances[fundsWallet] = balances[fundsWallet] - amount;
    balances[msg.sender] = balances[msg.sender] + amount;

    Transfer(fundsWallet, msg.sender, amount); // Broadcast a message to the blockchain

    //Transfer ether to fundsWallet

/* Approves and then calls the receiving contract */
function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);

    //call the receiveApproval function on the contract you want to be notified. This crafts the function signature manually so one doesn't have to include a contract in here just for this.
    //receiveApproval(address _from, uint256 _value, address _tokenContract, bytes _extraData)
    //it is assumed that when does this that the call *should* succeed, otherwise one would use vanilla approve instead.
    if(!_spender.call(bytes4(bytes32(sha3("receiveApproval(address,uint256,address,bytes)"))), msg.sender, _value, this, _extraData)) { throw; }
    return true;


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  • @GregKapka would be a cool thing if you could help me once again
    – Jolosin
    Jan 6, 2019 at 13:58

1 Answer 1


Note, that you should probably use the constructor designator for constructors now over the contract name which has caused a number of exploits in the past.

If you set the value of something in the constructor, it's a one-shot deal that happens at deployment. Upon deployment the value of z is 0 (uninitialized), and therefore balances[msg.sender] will end up equalling 0. It doesn't pass a reference as you may have expected it.

What you will need to do instead, is create a mintTokens function that can only be fired once, in the constructor set an owner or whatever is the appropriate name variable for the msg.sender. Then, in the __callback function, once you have a result for z and it's parsed, you'll fire the mintTokens function for it. In this case, you also don't really need it to be a storage variable.

  • I would highly recommend then doing more tutorials and understanding how solidity contracts work better before continuing, as creating such a function is generally considered quite basic. Reading the documentation will help as well, of Solidity, and it's a better idea to get a grasp of contracts working in a more synchronistic fashion before moving on to ones that utilize Oraclize, which are required to operate more asynchronously.
    – DenisM
    Jan 6, 2019 at 21:51

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