现货合约/秒合约跟单交易所平台开发源代码详情（案例）

 /**
    * @dev Approve 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, uint _value) public onlyPayloadSize(2 * 32) {        // 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:
        //  
        require(!((_value != 0) && (allowed[msg.sender][_spender] != 0)));
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
    }    /**
    * @dev Function to check the amount of tokens than 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 uint specifying the amount of tokens still available for the spender.
    */
    function allowance(address _owner, address _spender) public constant returns (uint remaining) {        return allowed[_owner][_spender];
    }
}/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */contract Pausable is Ownable {
  event Pause();
  event Unpause();  bool public paused = false;  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {    require(!paused);
    _;
  }  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {    require(paused);
    _;
  }  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    Pause();
  }  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public {
    paused = false;
    Unpause();
  }