I am new to Solidity and I have generated a Crowdsale contract using the following parameters on Ropsten test net.

Start Date    : 1514215525 which is equal to 12/25/2017 3:25pm
End Date      : 1514467525 which is equal to 12/28/2017 1:25pm
Rate          : 500
Address Wallet: "0x5bd6...........A491e7".

The code for the crowdsale is given below:

pragma solidity ^0.4.18;

contract ERC20Basic {
  uint256 public totalSupply;
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    uint256 c = a * b;
    assert(c / a == b);
    return c;

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;

contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  mapping(address => uint256) balances;

  * @dev transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    // SafeMath.sub will throw if there is not enough balance.
    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    Transfer(msg.sender, _to, _value);
    return true;

  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of.
  * @return An uint256 representing the amount owned by the passed address.
  function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];


contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender) public view returns (uint256);
  function transferFrom(address from, address to, uint256 value) public returns (bool);
  function approve(address spender, uint256 value) public returns (bool);
  event Approval(address indexed owner, address indexed spender, uint256 value);

contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;

   * @dev Transfer tokens from one address to another
   * @param _from address The address which you want to send tokens from
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amount of tokens to be transferred
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    Transfer(_from, _to, _value);
    return true;

   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;

   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param _owner address The address which owns the funds.
   * @param _spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];

   * approve should be called when allowed[_spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;

  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;


contract TOKKA is StandardToken {
    string public name = "TOKKA";
    string public symbol = "TOK";
    uint256 public decimals = 18;

    uint256 constant INITIAL_SUPPLY = 6000000 * 10**18;
    function TOKKA () public {
       balances[msg.sender] = INITIAL_SUPPLY;

contract Crowdsale {
  using SafeMath for uint256;

   // The token being sold
  TOKKA public token;

  // start and end timestamps where investments are allowed (both inclusive)
  uint256 public startTime;
  uint256 public endTime;

  // address where funds are collected
  address public wallet;

  // how many token units a buyer gets per wei
  uint256 public rate;

  // amount of raised money in wei
  uint256 public weiRaised;

  event TokenPurchase(address indexed purchaser, address indexed beneficiary, uint256 value, uint256 amount);

  function Crowdsale(uint256 _startTime, uint256 _endTime, uint256 _rate, address _wallet) public {
    require(_startTime >= now);
    require(_endTime >= _startTime);
    require(_rate > 0);
    require(_wallet != address(0));

    startTime = _startTime;
    endTime = _endTime;
    rate = _rate;
    wallet = _wallet;
    token = createTokenContract();

// creates the token to be sold.
// override this method to have crowdsale of a specific mintable token.
function createTokenContract() internal returns (TOKKA) {
    return new TOKKA();

  // fallback function can be used to buy tokens
  function () external payable {

  // low level token purchase function
function buyTokens(address beneficiary) public payable {
    require(beneficiary != address(0));

    uint256 weiAmount = msg.value;

    // calculate token amount to be created
    uint256 tokens = weiAmount.mul(rate);

    // update state
    weiRaised = weiRaised.add(weiAmount);

    // transfer tokens purchased 
    //ERC20(token).transfer(this, tokens);
    StandardToken(token).transfer(this, tokens);

    TokenPurchase(msg.sender, beneficiary, weiAmount, tokens);


  function forwardFunds() internal {

  function validPurchase() internal view returns (bool) {
    bool withinPeriod = now >= startTime && now <= endTime;
    bool nonZeroPurchase = msg.value != 0;
    return withinPeriod && nonZeroPurchase;

  function hasEnded() public view returns (bool) {
    return now > endTime;


contract CappedCrowdsale is Crowdsale {

  using SafeMath for uint256;

  uint256 public cap;

  function CappedCrowdsale(uint256 _cap) public {
    require(_cap > 0);
    cap = _cap;

  function validPurchase() internal view returns (bool) {
    bool withinCap = weiRaised.add(msg.value) <= cap;
    return super.validPurchase() && withinCap;

  function hasEnded() public view returns (bool) {
    bool capReached = weiRaised >= cap;
    return super.hasEnded() || capReached;


I have tried to send ether to this contract address after 15 minutes from the start date but transactions did not work for me but when i send ether on the next day (12/26/2017) at 01:07 Pm, the transactions worked fine. Please help me with this confusion. Thanks

  • 1
    Hi there. Can you post the code so people can take a look? – Richard Horrocks Dec 26 '17 at 11:14

Seems the contract is well written, are you considering that all times are GMT? Because as far as i can tell, you've asked this question at least one hour earlier than 2017/12/26 13:07 GMT

| improve this answer | |
  • I know this should be a comment, but my current reputation don't allow me to post them. Also, the "seems that the contract is well written" should be focused on 'seems' and only in what refers to the start_time parameter – Hari GTT Psicolabis Dec 26 '17 at 14:05
  • I was converting UTC time into unix time stamp using online converter and that was taking the value of the server on which the website is deployed and that time is different from my country Time. Now i am using another converter which is working fine for me. Thanks alot for your comments and for giving your precious time. – usman mehmood Dec 27 '17 at 10:40
  • But one thing i need to know about the above code. If the goal is not reached, for example our goal is to collect 250 ethers and we have collected 200 ethers and the crowdsale ended. Then what will be the scenario to gain 50 remaining tokens? Also how can we add Cap amount to the above code? – usman mehmood Dec 27 '17 at 10:46

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