openzeppelin-contracts/contracts/token/StandardToken.sol

pragma solidity ^0.4.8;


import './BasicToken.sol';
import './ERC20.sol';


/**
 * Standard ERC20 token
 *
 * https://github.com/ethereum/EIPs/issues/20
 * Based on code by FirstBlood:
 * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is BasicToken, ERC20 {

  mapping (address => mapping (address => uint)) allowed;

  function transferFrom(address _from, address _to, uint _value) {
    var _allowance = allowed[_from][msg.sender];

    // Check is not needed because safeSub(_allowance, _value) will already throw if this condition is not met
    // if (_value > _allowance) throw;

    balances[_to] = safeAdd(balances[_to], _value);
    balances[_from] = safeSub(balances[_from], _value);
    allowed[_from][msg.sender] = safeSub(_allowance, _value);
    Transfer(_from, _to, _value);
  }

  function approve(address _spender, uint _value) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
  }

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

}