pragma solidity ^0.4.11; import './BasicToken.sol'; import './ERC20.sol'; /** * @title Standard ERC20 token * * @dev Implementation of the basic standard token. * @dev https://github.com/ethereum/EIPs/issues/20 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol */ contract StandardToken is ERC20, BasicToken { mapping (address => mapping (address => uint256)) 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 amout of tokens to be transfered */ function transferFrom(address _from, address _to, uint256 _value) { var _allowance = allowed[_from][msg.sender]; // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met // if (_value > _allowance) throw; balances[_to] = balances[_to].add(_value); balances[_from] = balances[_from].sub(_value); allowed[_from][msg.sender] = _allowance.sub(_value); Transfer(_from, _to, _value); } /** * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender. * @param _spender The address which will spend the funds. * @param _value The amount of tokens to be spent. */ function approve(address _spender, uint256 _value) { // To change the approve amount you first have to reduce the addresses` // allowance to zero by calling `approve(_spender, 0)` if it is not // already 0 to mitigate the race condition described here: // https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 if ((_value != 0) && (allowed[msg.sender][_spender] != 0)) throw; allowed[msg.sender][_spender] = _value; Approval(msg.sender, _spender, _value); } /** * @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 specifing the amount of tokens still avaible for the spender. */ function allowance(address _owner, address _spender) constant returns (uint256 remaining) { return allowed[_owner][_spender]; } }