// Vulnerability label: ARTHM
pragma solidity ^0.4.19;
interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }
contract TokenERC20 {
string public name;
string public symbol;
uint8 public decimals = 18;  // decimals 可以有的小数点个数，最小的代币单位。18 是建议的默认值
uint256 public totalSupply;
// 用mapping保存每个地址对应的余额
mapping (address => uint256) public balanceOf;
// 存储对账号的控制
mapping (address => mapping (address => uint256)) public allowance;
// 事件，用来通知客户端交易发生
event Transfer(address indexed from, address indexed to, uint256 value);
// 事件，用来通知客户端代币被消费
event Burn(address indexed from, uint256 value);
/**
* 初始化构造
*/
function TokenERC20(uint256 initialSupply, string tokenName, string tokenSymbol) public {
totalSupply = initialSupply * 10 ** uint256(decimals);  // 供应的份额，份额跟最小的代币单位有关，份额 = 币数 * 10 ** decimals。
balanceOf[msg.sender] = totalSupply;                // 创建者拥有所有的代币
name = tokenName;                                   // 代币名称
symbol = tokenSymbol;                               // 代币符号
}
/**
* 代币交易转移的内部实现
*/
function _transfer(address _from, address _to, uint _value) internal {
// 确保目标地址不为0x0，因为0x0地址代表销毁
require(_to != 0x0);
// 检查发送者余额
require(balanceOf[_from] >= _value);
// 确保转移为正数个
require(balanceOf[_to] + _value > balanceOf[_to]);
// 以下用来检查交易，
uint previousBalances = balanceOf[_from] + balanceOf[_to];
// Subtract from the sender
balanceOf[_from] -= _value;
// Add the same to the recipient
balanceOf[_to] += _value;
Transfer(_from, _to, _value);
// 用assert来检查代码逻辑。
assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
}
/**
*  代币交易转移
* 从自己（创建交易者）账号发送`_value`个代币到 `_to`账号
*
* @param _to 接收者地址
* @param _value 转移数额
*/
function transfer(address _to, uint256 _value) public {
_transfer(msg.sender, _to, _value);
}
/**
* 账号之间代币交易转移
* @param _from 发送者地址
* @param _to 接收者地址
* @param _value 转移数额
*/
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
require(_value <= allowance[_from][msg.sender]);     // Check allowance
allowance[_from][msg.sender] -= _value;
_transfer(_from, _to, _value);
return true;
}
/**
* 设置某个地址（合约）可以创建交易者名义花费的代币数。
*
* 允许发送者`_spender` 花费不多于 `_value` 个代币
*
* @param _spender The address authorized to spend
* @param _value the max amount they can spend
*/
function approve(address _spender, uint256 _value) public
returns (bool success) {
allowance[msg.sender][_spender] = _value;
return true;
}
/**
* 设置允许一个地址（合约）以我（创建交易者）的名义可最多花费的代币数。
*
* @param _spender 被授权的地址（合约）
* @param _value 最大可花费代币数
* @param _extraData 发送给合约的附加数据
*/
function approveAndCall(address _spender, uint256 _value, bytes _extraData)
public
returns (bool success) {
tokenRecipient spender = tokenRecipient(_spender);
if (approve(_spender, _value)) {
// 通知合约
spender.receiveApproval(msg.sender, _value, this, _extraData);
return true;
}
}
/**
* 销毁我（创建交易者）账户中指定个代币
*/
function burn(uint256 _value) public returns (bool success) {
require(balanceOf[msg.sender] >= _value);   // Check if the sender has enough
balanceOf[msg.sender] -= _value;            // Subtract from the sender
totalSupply -= _value;                      // Updates totalSupply
Burn(msg.sender, _value);
return true;
}
/**
* 销毁用户账户中指定个代币
*
* Remove `_value` tokens from the system irreversibly on behalf of `_from`.
*
* @param _from the address of the sender
* @param _value the amount of money to burn
*/
function burnFrom(address _from, uint256 _value) public returns (bool success) {
require(balanceOf[_from] >= _value);                // Check if the targeted balance is enough
require(_value <= allowance[_from][msg.sender]);    // Check allowance
balanceOf[_from] -= _value;                         // Subtract from the targeted balance
allowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowance
totalSupply -= _value;                              // Update totalSupply
Burn(_from, _value);
return true;
}
}