StandardToken.sol 3.0 KB

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  1. pragma solidity ^0.4.11;
  2. import './BasicToken.sol';
  3. import './ERC20.sol';
  4. /**
  5. * @title Standard ERC20 token
  6. *
  7. * @dev Implementation of the basic standard token.
  8. * @dev https://github.com/ethereum/EIPs/issues/20
  9. * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
  10. */
  11. contract StandardToken is ERC20, BasicToken {
  12. mapping (address => mapping (address => uint256)) allowed;
  13. /**
  14. * @dev Transfer tokens from one address to another
  15. * @param _from address The address which you want to send tokens from
  16. * @param _to address The address which you want to transfer to
  17. * @param _value uint256 the amount of tokens to be transferred
  18. */
  19. function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
  20. require(_to != address(0));
  21. uint256 _allowance = allowed[_from][msg.sender];
  22. // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met
  23. // require (_value <= _allowance);
  24. balances[_from] = balances[_from].sub(_value);
  25. balances[_to] = balances[_to].add(_value);
  26. allowed[_from][msg.sender] = _allowance.sub(_value);
  27. Transfer(_from, _to, _value);
  28. return true;
  29. }
  30. /**
  31. * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
  32. * @param _spender The address which will spend the funds.
  33. * @param _value The amount of tokens to be spent.
  34. */
  35. function approve(address _spender, uint256 _value) public returns (bool) {
  36. allowed[msg.sender][_spender] = _value;
  37. Approval(msg.sender, _spender, _value);
  38. return true;
  39. }
  40. /**
  41. * @dev Function to check the amount of tokens that an owner allowed to a spender.
  42. * @param _owner address The address which owns the funds.
  43. * @param _spender address The address which will spend the funds.
  44. * @return A uint256 specifying the amount of tokens still available for the spender.
  45. */
  46. function allowance(address _owner, address _spender) public constant returns (uint256 remaining) {
  47. return allowed[_owner][_spender];
  48. }
  49. /**
  50. * approve should be called when allowed[_spender] == 0. To increment
  51. * allowed value is better to use this function to avoid 2 calls (and wait until
  52. * the first transaction is mined)
  53. * From MonolithDAO Token.sol
  54. */
  55. function increaseApproval (address _spender, uint _addedValue)
  56. returns (bool success) {
  57. allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
  58. Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
  59. return true;
  60. }
  61. function decreaseApproval (address _spender, uint _subtractedValue)
  62. returns (bool success) {
  63. uint oldValue = allowed[msg.sender][_spender];
  64. if (_subtractedValue > oldValue) {
  65. allowed[msg.sender][_spender] = 0;
  66. } else {
  67. allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
  68. }
  69. Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
  70. return true;
  71. }
  72. }