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| pragma solidity ^0.4.24;
import "./BasicToken.sol";
import "./ERC20.sol";
/**
* @title 标准 ERC20 token
*
* @dev 实现基础的标准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)) internal allowed;
/**
* @dev 从一个地址向另外一个地址转token
* @param _from 转账的from地址
* @param _to address 转账的to地址
* @param _value uint256 转账token数量
*/
function transferFrom(
address _from,
address _to,
uint256 _value
)
public
returns (bool)
{
// 做合法性检查
require(_to != address(0));
require(_value <= balances[_from]);
require(_value <= allowed[_from][msg.sender]);
//_from余额减去相应的金额
//_to余额加上相应的金额
//msg.sender可以从账户_from中转出的数量减少_value
balances[_from] = balances[_from].sub(_value);
balances[_to] = balances[_to].add(_value);
allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
// 触发Transfer事件
emit Transfer(_from, _to, _value);
return true;
}
/**
* @dev 批准传递的address以代表msg.sender花费指定数量的token
*
* 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 花费资金的地址
* @param _value 可以被花费的token数量
*/
function approve(address _spender, uint256 _value) public returns (bool) {
//记录msg.sender允许_spender动用的token
allowed[msg.sender][_spender] = _value;
//触发Approval事件
emit Approval(msg.sender, _spender, _value);
return true;
}
/**
* @dev 函数检查所有者允许的_spender花费的token数量
* @param _owner address 资金所有者地址.
* @param _spender address 花费资金的spender的地址.
* @return A uint256 指定_spender仍可用token的数量。
*/
function allowance(
address _owner,
address _spender
)
public
view
returns (uint256)
{
//允许_spender从_owner中转出的token数
return allowed[_owner][_spender];
}
/**
* @dev 增加所有者允许_spender花费代币的数量。
*
* allowed[_spender] == 0时approve应该被调用. 增加allowed值最好使用此函数避免2此调用（等待知道第一笔交易被挖出）
* From MonolithDAO Token.sol
* @param _spender 花费资金的地址
* @param _addedValue 用于增加允许动用的token牌数量
*/
function increaseApproval(
address _spender,
uint _addedValue
)
public
returns (bool)
{
//在之前允许的数量上增加_addedValue
allowed[msg.sender][_spender] = (
allowed[msg.sender][_spender].add(_addedValue));
//触发Approval事件
emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
return true;
}
/**
* @dev 减少所有者允许_spender花费代币的数量
*
* allowed[_spender] == 0时approve应该被调用. 减少allowed值最好使用此函数避免2此调用（等待知道第一笔交易被挖出）
* From MonolithDAO Token.sol
* @param _spender 花费资金的地址
* @param _subtractedValue 用于减少允许动用的token牌数量
*/
function decreaseApproval(
address _spender,
uint _subtractedValue
)
public
returns (bool)
{
uint oldValue = allowed[msg.sender][_spender];
if (_subtractedValue > oldValue) {
//减少的数量少于之前允许的数量，则清零
allowed[msg.sender][_spender] = 0;
} else {
//减少对应的_subtractedValue数量
allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
}
//触发Approval事件
emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
return true;
}
}
|
