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7.6. 代币合约官方文档

7.6.1. ERC20

https://github.com/ethereum/EIPs/issues/20

https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md

合约源码：https://github.com/ConsenSys/Tokens/tree/master/contracts/eip20

https://theethereum.wiki/w/index.php/ERC20_Token_Standard

			
 // ----------------------------------------------------------------------------
 // ERC20 Token Standard Interface
 // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
 // ----------------------------------------------------------------------------
contract ERC20 {
      function name() constant returns (string name)
      function symbol() constant returns (string symbol)
      function decimals() constant returns (uint8 decimals)
      function totalSupply() constant returns (uint totalSupply);
      function balanceOf(address _owner) constant returns (uint balance);
      function transfer(address _to, uint _value) returns (bool success);
      function transferFrom(address _from, address _to, uint _value) returns (bool success);
      function approve(address _spender, uint _value) returns (bool success);
      function allowance(address _owner, address _spender) constant returns (uint remaining);
      event Transfer(address indexed _from, address indexed _to, uint _value);
      event Approval(address indexed _owner, address indexed _spender, uint _value);
}			
			
			

7.6.1.1. 基本Token 官方提供的例子

这个例子仅仅用来初学使用，请不用使用在生产环境。

提供例子的地址： https://ethereum.org/token

这个例子中没有涉及合约管理者，所以任何人都可以操作这个合约。例如这个减持的函数burn() 人人都可以调用。所以这个例子只能用来学习ERC20合约开发，相当于Helloword 程序。

			
pragma solidity ^0.4.16;

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract TokenERC20 {
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    // 18 decimals is the strongly suggested default, avoid changing it
    uint256 public totalSupply;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);

    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);

    /**
     * Constructor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function TokenERC20(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
    }

    /**
     * Internal transfer, only can be called by this contract
     */
    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
        // Check if the sender has enough
        require(balanceOf[_from] >= _value);
        // Check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);
        // Save this for an assertion in the future
        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);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    /**
     * Transfer tokens
     *
     * Send `_value` tokens to `_to` from your account
     *
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    /**
     * Transfer tokens from other address
     *
     * Send `_value` tokens to `_to` on behalf of `_from`
     *
     * @param _from The address of the sender
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    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;
    }

    /**
     * Set allowance for other address
     *
     * Allows `_spender` to spend no more than `_value` tokens on your behalf
     *
     * @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;
    }

    /**
     * Set allowance for other address and notify
     *
     * Allows `_spender` to spend no more than `_value` tokens on your behalf, and then ping the contract about it
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     * @param _extraData some extra information to send to the approved contract
     */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly
     *
     * @param _value the amount of money to burn
     */
    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;
    }

    /**
     * Destroy tokens from other account
     *
     * 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;
    }
}
			
			
				

7.6.1.2. 官方提供的例子 ADVANCED TOKEN

提供例子的地址： https://ethereum.org/token 网页的下方

这个例子已经比较完善，但仍不能够用在生产环境，因为 function burn(uint256 _value) public returns (bool success) 仍然没有控制访问权限。

如果在生产环境使用这个合约你需要修改两处

			
function burn(uint256 _value) public returns (bool success)
改为
function burn(uint256 _value) onlyOwner public returns (bool success)


function burnFrom(address _from, uint256 _value) public returns (bool success)
改为
function burnFrom(address _from, uint256 _value) onlyOwner public returns (bool success)
			
				

这样合约就很安全了。只能创建者可以减持代币。

			
pragma solidity ^0.4.16;

contract owned {
    address public owner;

    function owned() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) onlyOwner public {
        owner = newOwner;
    }
}

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract TokenERC20 {
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    // 18 decimals is the strongly suggested default, avoid changing it
    uint256 public totalSupply;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);

    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function TokenERC20(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
    }

    /**
     * Internal transfer, only can be called by this contract
     */
    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
        // Check if the sender has enough
        require(balanceOf[_from] >= _value);
        // Check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);
        // Save this for an assertion in the future
        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);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    /**
     * Transfer tokens
     *
     * Send `_value` tokens to `_to` from your account
     *
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    /**
     * Transfer tokens from other address
     *
     * Send `_value` tokens to `_to` in behalf of `_from`
     *
     * @param _from The address of the sender
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    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;
    }

    /**
     * Set allowance for other address
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf
     *
     * @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;
    }

    /**
     * Set allowance for other address and notify
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     * @param _extraData some extra information to send to the approved contract
     */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly
     *
     * @param _value the amount of money to burn
     */
    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;
    }

    /**
     * Destroy tokens from other account
     *
     * 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;
    }
}

/******************************************/
/*       ADVANCED TOKEN STARTS HERE       */
/******************************************/

contract MyAdvancedToken is owned, TokenERC20 {

    uint256 public sellPrice;
    uint256 public buyPrice;

    mapping (address => bool) public frozenAccount;

    /* This generates a public event on the blockchain that will notify clients */
    event FrozenFunds(address target, bool frozen);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    function MyAdvancedToken(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) TokenERC20(initialSupply, tokenName, tokenSymbol) public {}

    /* Internal transfer, only can be called by this contract */
    function _transfer(address _from, address _to, uint _value) internal {
        require (_to != 0x0);                               // Prevent transfer to 0x0 address. Use burn() instead
        require (balanceOf[_from] >= _value);               // Check if the sender has enough
        require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
        require(!frozenAccount[_from]);                     // Check if sender is frozen
        require(!frozenAccount[_to]);                       // Check if recipient is frozen
        balanceOf[_from] -= _value;                         // Subtract from the sender
        balanceOf[_to] += _value;                           // Add the same to the recipient
        Transfer(_from, _to, _value);
    }

    /// @notice Create `mintedAmount` tokens and send it to `target`
    /// @param target Address to receive the tokens
    /// @param mintedAmount the amount of tokens it will receive
    function mintToken(address target, uint256 mintedAmount) onlyOwner public {
        balanceOf[target] += mintedAmount;
        totalSupply += mintedAmount;
        Transfer(0, this, mintedAmount);
        Transfer(this, target, mintedAmount);
    }

    /// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
    /// @param target Address to be frozen
    /// @param freeze either to freeze it or not
    function freezeAccount(address target, bool freeze) onlyOwner public {
        frozenAccount[target] = freeze;
        FrozenFunds(target, freeze);
    }

    /// @notice Allow users to buy tokens for `newBuyPrice` eth and sell tokens for `newSellPrice` eth
    /// @param newSellPrice Price the users can sell to the contract
    /// @param newBuyPrice Price users can buy from the contract
    function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner public {
        sellPrice = newSellPrice;
        buyPrice = newBuyPrice;
    }

    /// @notice Buy tokens from contract by sending ether
    function buy() payable public {
        uint amount = msg.value / buyPrice;               // calculates the amount
        _transfer(this, msg.sender, amount);              // makes the transfers
    }

    /// @notice Sell `amount` tokens to contract
    /// @param amount amount of tokens to be sold
    function sell(uint256 amount) public {
        require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
        _transfer(msg.sender, this, amount);              // makes the transfers
        msg.sender.transfer(amount * sellPrice);          // sends ether to the seller. It's important to do this last to avoid recursion attacks
    }
}			
			
				

下面就分析一下这个合约

在许多应用场景中，需要管理发行的代币，为了对代币进行管理，需要给合约添加一个管理者，为此创建了 owned 合约。

contract owned {
    address public owner;

    function owned() {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    // 实现所有权转移
    function transferOwnership(address newOwner) onlyOwner {
        owner = newOwner;
    }
}
这个合约重要的是加入了一个函数修改器（Function Modifiers）onlyOwner，函数修改器是一个合约属性，可以被继承，还能被重写。它用于在函数执行前检查某种前置条件。

代币增发, 实现代币增发，代币增发就如同央行印钞票一样，想必很多人都需要这样的功能。给合约添加以下的方法：

			
function mintToken(address target, uint256 mintedAmount) onlyOwner {
        balanceOf[target] += mintedAmount;
        totalSupply += mintedAmount;
        Transfer(0, owner, mintedAmount);
        Transfer(owner, target, mintedAmount);
    }
注意onlyOwner修改器添加在函数末尾，这表示只有owner才能调用这用函数。
他的功能很简单，就是给指定的账户增加代币，同时增加总供应量。
			
				

资产冻结

有时为了监管的需要，需要实现冻结某些账户，冻结后，其资产仍在账户，但是不允许交易，之道解除冻结。

			
给合约添加以下的变量和方法（可以添加到合约的任何地方，但是建议把mapping加到和其他mapping一起，event也是如此）：

mapping (address => bool) public frozenAccount;
event FrozenFunds(address target, bool frozen);

function freezeAccount(address target, bool freeze) onlyOwner {
    frozenAccount[target] = freeze;
    FrozenFunds(target, freeze);
}
单单以上的代码还无法冻结，需要把他加入到transfer函数中才能真正生效，因此修改transfer函数

function transfer(address _to, uint256 _value) {
        require(!frozenAccount[msg.sender]);
        ...
}
这样在转账前，对发起交易的账号做一次检查，只有不是被冻结的账号才能转账。
			
				

代币买卖（兑换）

			

可以自己的货币中实现代币与其他数字货币（ether 或其他tokens）的兑换机制。有了这个功能，我们的合约就可以在一买一卖中赚利润了。

先来设置下买卖价格

uint256 public sellPrice;
uint256 public buyPrice;

function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner {
    sellPrice = newSellPrice;
    buyPrice = newBuyPrice;
}
setPrices()添加了onlyOwner修改器，注意买卖的价格单位是wei（最小的货币单位： 1 eth = 1000000000000000000 wei)

添加来添加买卖函数:

function buy() payable returns (uint amount){
    amount = msg.value / buyPrice;                    // calculates the amount
    require(balanceOf[this] >= amount);               // checks if it has enough to sell
    balanceOf[msg.sender] += amount;                  // adds the amount to buyer's balance
    balanceOf[this] -= amount;                        // subtracts amount from seller's balance
    Transfer(this, msg.sender, amount);               // execute an event reflecting the change
    return amount;                                    // ends function and returns
}

function sell(uint amount) returns (uint revenue){
    require(balanceOf[msg.sender] >= amount);         // checks if the sender has enough to sell
    balanceOf[this] += amount;                        // adds the amount to owner's balance
    balanceOf[msg.sender] -= amount;                  // subtracts the amount from seller's balance
    revenue = amount * sellPrice;
    msg.sender.transfer(revenue);                     // sends ether to the seller: it's important to do this last to prevent recursion attacks
    Transfer(msg.sender, this, amount);               // executes an event reflecting on the change
    return revenue;                                   // ends function and returns
}
加入了买卖功能后，要求我们在创建合约时发送足够的以太币，以便合约有能力回购市面上的代币，否则合约将破产，用户没法先合约卖代币。
			
				

实现Gas的自动补充

			
以太坊中的交易时需要gas（支付给矿工的费用，费用以ether来支付）。而如果用户没有以太币，只有代币的情况（或者我们想向用户隐藏以太坊的细节），就需要自动补充gas的功能。这个功能将使我们代币更加好用。

自动补充的逻辑是这样了，在执行交易之前，我们判断用户的余额（用来支付矿工的费用），如果用户的余额非常少（低于某个阈值时）可能影响到交易进行，合约自动售出一部分代币来补充余额，以帮助用户顺利完成交易。

先来设定余额阈值：

uint minBalanceForAccounts;

    function setMinBalance(uint minimumBalanceInFinney) onlyOwner {
         minBalanceForAccounts = minimumBalanceInFinney * 1 finney;
    }
finney 是货币单位 1 finney = 0.001eth
然后交易中加入对用户的余额的判断。

function transfer(address _to, uint256 _value) {
    ...
    if(msg.sender.balance < minBalanceForAccounts)
        sell((minBalanceForAccounts - msg.sender.balance) / sellPrice);
    if(_to.balance<minBalanceForAccounts)   // 可选，让接受者也补充余额，以便接受者使用代币。
        _to.send(sell((minBalanceForAccounts - _to.balance) / sellPrice));
}			
			
				

7.6.1.3. Netkiller Basic Token 的例子

下面是我一个合约例子仅供参考，为了部署方便我将所有内容都写入在一个文件中。

合约下载地址： https://github.com/ibook/TokenERC20/blob/master/contracts/TokenERC20.sol

有些场景我们需要记录一些数据在区块链上，这个合约增加了 data 数据支持

			
  function transfer(address _to, uint256 _value, bytes _data) public returns (bool) {
    require(_to != address(this));
    transfer(_to, _value);
    require(_to.call(_data));
    return true;
  }			
			
				

完整的例子如下

			
pragma solidity ^0.4.20;

// Author: netkiller <netkiller@msn.com>
// Homepage: http://www.netkiller.cn

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract TokenERC20 {
    address public owner;
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    // 18 decimals is the strongly suggested default, avoid changing it
    uint256 public totalSupply;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);

    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);

    mapping (address => bool) public frozenAccount;
    event FrozenFunds(address target, bool frozen);

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function TokenERC20(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        owner = msg.sender;
        
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    /**
     * Internal transfer, only can be called by this contract
     */
    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
        // Check if the sender has enough
        require(balanceOf[_from] >= _value);
        // Check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);
        // Save this for an assertion in the future
        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);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }
    
    function transfer(address _to, uint256 _value) public {
        require(!frozenAccount[msg.sender]);
        _transfer(msg.sender, _to, _value);
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(!frozenAccount[msg.sender]);
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function burn(uint256 _value) onlyOwner 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;
    }


    function burnFrom(address _from, uint256 _value) onlyOwner 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;
    }


  function transfer(address _to, uint256 _value, bytes _data) public returns (bool) {
    require(_to != address(this));
    transfer(_to, _value);
    require(_to.call(_data));
    return true;
  }

  function transferFrom(address _from, address _to, uint256 _value, bytes _data) public returns (bool) {
    require(_to != address(this));

    transferFrom(_from, _to, _value);

    require(_to.call(_data));
    return true;
  }

  function approve(address _spender, uint256 _value, bytes _data) public returns (bool) {
    require(_spender != address(this));

    approve(_spender, _value);

    require(_spender.call(_data));

    return true;
  }

    
    function transferOwnership(address _owner) onlyOwner public {
        owner = _owner;
    }
    function mintToken(address target, uint256 mintedAmount) public onlyOwner {
        balanceOf[target] += mintedAmount;
        totalSupply += mintedAmount;
        Transfer(0, owner, mintedAmount);
        Transfer(owner, target, mintedAmount);
    }

    function freezeAccount(address target, bool freeze) public onlyOwner {
        frozenAccount[target] = freeze;
        FrozenFunds(target, freeze);
    }
}
			
				

7.6.1.4. Netkiller ADVANCED TOKEN

			
pragma solidity ^0.4.20;

/******************************************/
/*       Netkiller ADVANCED TOKEN         */
/******************************************/
/* Author netkiller <netkiller@msn.com>   */
/* Home http://www.netkiller.cn           */
/* Version 2018-03-05                     */
/******************************************/

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract NetkillerAdvancedToken {
    address public owner;
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    // 18 decimals is the strongly suggested default, avoid changing it
    uint256 public totalSupply;
    
    uint256 public sellPrice;
    uint256 public buyPrice;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);

    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
    
    mapping (address => bool) public frozenAccount;

    /* This generates a public event on the blockchain that will notify clients */
    event FrozenFunds(address target, bool frozen);

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function NetkillerAdvancedToken(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        owner = msg.sender;
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }
    function transferOwnership(address newOwner) onlyOwner public {
        owner = newOwner;
    }
 
    /* Internal transfer, only can be called by this contract */
    function _transfer(address _from, address _to, uint _value) internal {
        require (_to != 0x0);                               // Prevent transfer to 0x0 address. Use burn() instead
        require (balanceOf[_from] >= _value);               // Check if the sender has enough
        require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
        require(!frozenAccount[_from]);                     // Check if sender is frozen
        require(!frozenAccount[_to]);                       // Check if recipient is frozen
        balanceOf[_from] -= _value;                         // Subtract from the sender
        balanceOf[_to] += _value;                           // Add the same to the recipient
        Transfer(_from, _to, _value);
    }

    /**
     * Transfer tokens
     *
     * Send `_value` tokens to `_to` from your account
     *
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    /**
     * Transfer tokens from other address
     *
     * Send `_value` tokens to `_to` in behalf of `_from`
     *
     * @param _from The address of the sender
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    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;
    }

    /**
     * Set allowance for other address
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf
     *
     * @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;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * Set allowance for other address and notify
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     * @param _extraData some extra information to send to the approved contract
     */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly
     *
     * @param _value the amount of money to burn
     */
    function burn(uint256 _value) onlyOwner 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;
    }

    /**
     * Destroy tokens from other account
     *
     * 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) onlyOwner 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;
    }

    /// @notice Create `mintedAmount` tokens and send it to `target`
    /// @param target Address to receive the tokens
    /// @param mintedAmount the amount of tokens it will receive
    function mintToken(address target, uint256 mintedAmount) onlyOwner public {
        balanceOf[target] += mintedAmount;
        totalSupply += mintedAmount;
        Transfer(0, this, mintedAmount);
        Transfer(this, target, mintedAmount);
    }

    /// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
    /// @param target Address to be frozen
    /// @param freeze either to freeze it or not
    function freezeAccount(address target, bool freeze) onlyOwner public {
        frozenAccount[target] = freeze;
        FrozenFunds(target, freeze);
    }

    /// @notice Allow users to buy tokens for `newBuyPrice` eth and sell tokens for `newSellPrice` eth
    /// @param newSellPrice Price the users can sell to the contract
    /// @param newBuyPrice Price users can buy from the contract
    function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner public {
        sellPrice = newSellPrice;
        buyPrice = newBuyPrice;
    }

    /// @notice Buy tokens from contract by sending ether
    function buy() payable public {
        uint amount = msg.value / buyPrice;               // calculates the amount
        _transfer(this, msg.sender, amount);              // makes the transfers
    }

    /// @notice Sell `amount` tokens to contract
    /// @param amount amount of tokens to be sold
    function sell(uint256 amount) public {
        require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
        _transfer(msg.sender, this, amount);              // makes the transfers
        msg.sender.transfer(amount * sellPrice);          // sends ether to the seller. It's important to do this last to avoid recursion attacks
    }
    
  function transfer(address _to, uint256 _value, bytes _data) public returns (bool) {
    require(_to != address(this));
    transfer(_to, _value);
    require(_to.call(_data));
    return true;
  }

  function transferFrom(address _from, address _to, uint256 _value, bytes _data) public returns (bool) {
    require(_to != address(this));

    transferFrom(_from, _to, _value);

    require(_to.call(_data));
    return true;
  }

  function approve(address _spender, uint256 _value, bytes _data) public returns (bool) {
    require(_spender != address(this));

    approve(_spender, _value);

    require(_spender.call(_data));

    return true;
  }
    
}			
			
				

7.6.1.5. 空投代币

			
uint totalSupply = 100000000 ether; 	// 总发行量
uint currentTotalAirdrop = 0;    		// 已经空投数量
uint airdrop = 1 ether;        		// 单个账户空投数量

// 存储是否空投过
mapping(address => bool) touched;

// 修改后的balanceOf方法
function balanceOf(address _owner) public view returns (uint256 balance) {    
    if (!touched[_owner] && currentTotalAirdrop < totalSupply) {
        touched[_owner] = true;
        currentTotalAirdrop += airdrop;
        balances[_owner] += airdrop;
    }    
    return balances[_owner];
}
			
				

7.6.1.5.1. 案例一

				
pragma solidity ^0.4.8;

contract ERC20Interface {
    function totalSupply() public constant returns (uint256 supply);
    function balance() public constant returns (uint256);
    function balanceOf(address _owner) public constant returns (uint256);
    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
    function approve(address _spender, uint256 _value) public returns (bool success);
    function allowance(address _owner, address _spender) public constant returns (uint256 remaining);

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

// penispenispenispenis
// YOU get a penis, and YOU get a penis, and YOU get a penis!
contract Penis is ERC20Interface {
    string public constant symbol = "PNS";
    string public constant name = "Penis";
    uint8 public constant decimals = 2;

    uint256 _totalSupply = 0;
    uint256 _airdropAmount = 8008135;
    uint256 _cutoff = _airdropAmount * 80085;

    mapping(address => uint256) balances;
    mapping(address => bool) initialized;

    // Penis accepts request to tip-touch another Penis
    mapping(address => mapping (address => uint256)) allowed;

    function Penis() {
        initialized[msg.sender] = true;
        balances[msg.sender] = _airdropAmount * 8008;
        _totalSupply = balances[msg.sender];
    }

    function totalSupply() constant returns (uint256 supply) {
        return _totalSupply;
    }

    // What's my girth?
    function balance() constant returns (uint256) {
        return getBalance(msg.sender);
    }

    // What is the length of a particular Penis?
    function balanceOf(address _address) constant returns (uint256) {
        return getBalance(_address);
    }

    // Tenderly remove hand from Penis and place on another Penis
    function transfer(address _to, uint256 _amount) returns (bool success) {
        initialize(msg.sender);

        if (balances[msg.sender] >= _amount
            && _amount > 0) {
            initialize(_to);
            if (balances[_to] + _amount > balances[_to]) {

                balances[msg.sender] -= _amount;
                balances[_to] += _amount;

                Transfer(msg.sender, _to, _amount);

                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    // Perform the inevitable actions which cause release of that which each Penis
    // is built to deliver. In EtherPenisLand there are only Penises, so this 
    // allows the transmission of one Penis's payload (or partial payload but that
    // is not as much fun) INTO another Penis. This causes the Penisae to change 
    // form such that all may see the glory they each represent. Erections.
    function transferFrom(address _from, address _to, uint256 _amount) returns (bool success) {
        initialize(_from);

        if (balances[_from] >= _amount
            && allowed[_from][msg.sender] >= _amount
            && _amount > 0) {
            initialize(_to);
            if (balances[_to] + _amount > balances[_to]) {

                balances[_from] -= _amount;
                allowed[_from][msg.sender] -= _amount;
                balances[_to] += _amount;

                Transfer(_from, _to, _amount);

                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    // Allow splooger to cause a payload release from your Penis, multiple times, up to 
    // the point at which no further release is possible..
    function approve(address _spender, uint256 _amount) returns (bool success) {
        allowed[msg.sender][_spender] = _amount;
        Approval(msg.sender, _spender, _amount);
        return true;
    }

    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    // internal privats
    function initialize(address _address) internal returns (bool success) {
        if (_totalSupply < _cutoff && !initialized[_address]) {
            initialized[_address] = true;
            balances[_address] = _airdropAmount;
            _totalSupply += _airdropAmount;
        }
        return true;
    }

    function getBalance(address _address) internal returns (uint256) {
        if (_totalSupply < _cutoff && !initialized[_address]) {
            return balances[_address] + _airdropAmount;
        }
        else {
            return balances[_address];
        }
    }
}				
				
					

7.6.1.5.2. 案例二

			
pragma solidity ^0.4.8;

contract ERC20Interface {
    function totalSupply() public constant returns (uint256 supply);
    function balance() public constant returns (uint256);
    function balanceOf(address _owner) public constant returns (uint256);
    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
    function approve(address _spender, uint256 _value) public returns (bool success);
    function allowance(address _owner, address _spender) public constant returns (uint256 remaining);

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

contract Simoleon is ERC20Interface {
    string public constant symbol = "SIM";
    string public constant name = "Simoleon";
    uint8 public constant decimals = 2;

    uint256 _totalSupply = 0;
    uint256 _airdropAmount = 1000000;
    uint256 _cutoff = _airdropAmount * 10000;

    mapping(address => uint256) balances;
    mapping(address => bool) initialized;

    // Owner of account approves the transfer of an amount to another account
    mapping(address => mapping (address => uint256)) allowed;

    function Simoleon() {
        initialized[msg.sender] = true;
        balances[msg.sender] = _airdropAmount * 1000;
        _totalSupply = balances[msg.sender];
    }

    function totalSupply() constant returns (uint256 supply) {
        return _totalSupply;
    }

    // What's my balance?
    function balance() constant returns (uint256) {
        return getBalance(msg.sender);
    }

    // What is the balance of a particular account?
    function balanceOf(address _address) constant returns (uint256) {
        return getBalance(_address);
    }

    // Transfer the balance from owner's account to another account
    function transfer(address _to, uint256 _amount) returns (bool success) {
        initialize(msg.sender);

        if (balances[msg.sender] >= _amount
            && _amount > 0) {
            initialize(_to);
            if (balances[_to] + _amount > balances[_to]) {

                balances[msg.sender] -= _amount;
                balances[_to] += _amount;

                Transfer(msg.sender, _to, _amount);

                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    // Send _value amount of tokens from address _from to address _to
    // The transferFrom method is used for a withdraw workflow, allowing contracts to send
    // tokens on your behalf, for example to "deposit" to a contract address and/or to charge
    // fees in sub-currencies; the command should fail unless the _from account has
    // deliberately authorized the sender of the message via some mechanism; we propose
    // these standardized APIs for approval:
    function transferFrom(address _from, address _to, uint256 _amount) returns (bool success) {
        initialize(_from);

        if (balances[_from] >= _amount
            && allowed[_from][msg.sender] >= _amount
            && _amount > 0) {
            initialize(_to);
            if (balances[_to] + _amount > balances[_to]) {

                balances[_from] -= _amount;
                allowed[_from][msg.sender] -= _amount;
                balances[_to] += _amount;

                Transfer(_from, _to, _amount);

                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    // Allow _spender to withdraw from your account, multiple times, up to the _value amount.
    // If this function is called again it overwrites the current allowance with _value.
    function approve(address _spender, uint256 _amount) returns (bool success) {
        allowed[msg.sender][_spender] = _amount;
        Approval(msg.sender, _spender, _amount);
        return true;
    }

    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    // internal private functions
    function initialize(address _address) internal returns (bool success) {
        if (_totalSupply < _cutoff && !initialized[_address]) {
            initialized[_address] = true;
            balances[_address] = _airdropAmount;
            _totalSupply += _airdropAmount;
        }
        return true;
    }

    function getBalance(address _address) internal returns (uint256) {
        if (_totalSupply < _cutoff && !initialized[_address]) {
            return balances[_address] + _airdropAmount;
        }
        else {
            return balances[_address];
        }
    }
}			
			
					

7.6.1.5.3. 案例三

				
pragma solidity ^0.4.18;


library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    require(c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a / b;
    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a);
    return c;
  }
}


contract Ownable {
  address public owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  function Ownable() public {
    owner = msg.sender;
  }

  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}


contract SurpriseToken is Ownable{
    
    using SafeMath for uint256;
    
    string public constant name       = "SURPRISE";
    string public constant symbol     = "SPS";
    uint32 public constant decimals   = 18;
    uint256 public totalSupply        = 208932000 ether;
    uint256 public currentTotalSupply = 0;
    uint256 startBalance              = 276 ether;
    
    mapping(address => bool) touched;
    mapping(address => uint256) balances;
    mapping (address => mapping (address => uint256)) internal allowed;
    
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
    

    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));

        if( !touched[msg.sender] && currentTotalSupply < totalSupply ){
            balances[msg.sender] = balances[msg.sender].add( startBalance );
            touched[msg.sender] = true;
            currentTotalSupply = currentTotalSupply.add( startBalance );
        }
        
        require(_value <= balances[msg.sender]);
        
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
    
        Transfer(msg.sender, _to, _value);
        return true;
    }
  

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));
        
        require(_value <= allowed[_from][msg.sender]);
        
        if( !touched[_from] && currentTotalSupply < totalSupply ){
            touched[_from] = true;
            balances[_from] = balances[_from].add( startBalance );
            currentTotalSupply = currentTotalSupply.add( startBalance );
        }
        
        require(_value <= balances[_from]);
        
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        Transfer(_from, _to, _value);
        return true;
    }


    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }


    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
     }


    function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }


    function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue) {
          allowed[msg.sender][_spender] = 0;
        } else {
          allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
     }
    

    function getBalance(address _a) internal constant returns(uint256)
    {
        if( currentTotalSupply < totalSupply ){
            if( touched[_a] )
                return balances[_a];
            else
                return balances[_a].add( startBalance );
        } else {
            return balances[_a];
        }
    }
    

    function balanceOf(address _owner) public view returns (uint256 balance) {
        return getBalance( _owner );
    }
}				
				
					

7.6.2. ERC223 token standard reference implementation.

https://github.com/Dexaran/ERC223-token-standard

ERC223是以太坊上最新的代币(token)接口标准,主要是为了解决ERC220代币转账丢失问题

ERC220接口以transfer为例:

		
// @notice send `_value` token to `_to` from `msg.sender` 
// @param _to The address of the recipient 
// @param _value The amount of token to be transferred 
// @return Whether the transfer was successful or not 
function transfer(address _to, uint256 _value) public returns (bool success);


		
			

transfer的功能非常简单，给一个指定地址转多少代币。

但是当初设计的时候没有考虑到的一个问题就是如果接收者是一个智能合约,那么合约是没法感知自己收到了多少token的.

ERC223 中的方法定义

		
function transfer(address _to, uint _value) public returns (bool ok);
function transfer(address _to, uint _value, bytes _data) public returns (bool ok);
function transfer(address _to, uint _value, bytes _data, string _custom_fallback)		
		
			

除此之外 ERC223 还提供了安全的数学运算方法。

		
pragma solidity ^0.4.11;


/**
 * Math operations with safety checks
 */
library SafeMath {
  function mul(uint a, uint b) internal returns (uint) {
    uint c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function div(uint a, uint b) internal returns (uint) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  function sub(uint a, uint b) internal returns (uint) {
    assert(b <= a);
    return a - b;
  }

  function add(uint a, uint b) internal returns (uint) {
    uint c = a + b;
    assert(c >= a);
    return c;
  }

  function max64(uint64 a, uint64 b) internal constant returns (uint64) {
    return a >= b ? a : b;
  }

  function min64(uint64 a, uint64 b) internal constant returns (uint64) {
    return a < b ? a : b;
  }

  function max256(uint256 a, uint256 b) internal constant returns (uint256) {
    return a >= b ? a : b;
  }

  function min256(uint256 a, uint256 b) internal constant returns (uint256) {
    return a < b ? a : b;
  }

  function assert(bool assertion) internal {
    if (!assertion) {
      throw;
    }
  }
}		
		
			

ERC223 接口

		
pragma solidity ^0.4.11;

contract ERC223Interface {
    uint public totalSupply;
    function balanceOf(address who) constant returns (uint);
    function transfer(address to, uint value);
    function transfer(address to, uint value, bytes data);
    event Transfer(address indexed from, address indexed to, uint value, bytes data);
}
		
			

		
pragma solidity ^0.4.11;

 /**
 * @title Contract that will work with ERC223 tokens.
 */
 
contract ERC223ReceivingContract { 
/**
 * @dev Standard ERC223 function that will handle incoming token transfers.
 *
 * @param _from  Token sender address.
 * @param _value Amount of tokens.
 * @param _data  Transaction metadata.
 */
    function tokenFallback(address _from, uint _value, bytes _data);
}		
		
			

		
pragma solidity ^0.4.11;

import './ERC223_interface.sol';
import './ERC223_receiving_contract.sol';
import '././SafeMath.sol';

/**
 * @title Reference implementation of the ERC223 standard token.
 */
contract ERC223Token is ERC223Interface {
    using SafeMath for uint;

    mapping(address => uint) balances; // List of user balances.
    
    /**
     * @dev Transfer the specified amount of tokens to the specified address.
     *      Invokes the `tokenFallback` function if the recipient is a contract.
     *      The token transfer fails if the recipient is a contract
     *      but does not implement the `tokenFallback` function
     *      or the fallback function to receive funds.
     *
     * @param _to    Receiver address.
     * @param _value Amount of tokens that will be transferred.
     * @param _data  Transaction metadata.
     */
    function transfer(address _to, uint _value, bytes _data) {
        // Standard function transfer similar to ERC20 transfer with no _data .
        // Added due to backwards compatibility reasons .
        uint codeLength;

        assembly {
            // Retrieve the size of the code on target address, this needs assembly .
            codeLength := extcodesize(_to)
        }

        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        if(codeLength>0) {
            ERC223ReceivingContract receiver = ERC223ReceivingContract(_to);
            receiver.tokenFallback(msg.sender, _value, _data);
        }
        Transfer(msg.sender, _to, _value, _data);
    }
    
    /**
     * @dev Transfer the specified amount of tokens to the specified address.
     *      This function works the same with the previous one
     *      but doesn't contain `_data` param.
     *      Added due to backwards compatibility reasons.
     *
     * @param _to    Receiver address.
     * @param _value Amount of tokens that will be transferred.
     */
    function transfer(address _to, uint _value) {
        uint codeLength;
        bytes memory empty;

        assembly {
            // Retrieve the size of the code on target address, this needs assembly .
            codeLength := extcodesize(_to)
        }

        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        if(codeLength>0) {
            ERC223ReceivingContract receiver = ERC223ReceivingContract(_to);
            receiver.tokenFallback(msg.sender, _value, empty);
        }
        Transfer(msg.sender, _to, _value, empty);
    }

    
    /**
     * @dev Returns balance of the `_owner`.
     *
     * @param _owner   The address whose balance will be returned.
     * @return balance Balance of the `_owner`.
     */
    function balanceOf(address _owner) constant returns (uint balance) {
        return balances[_owner];
    }
}
		
			

7.6.3. ERC721 - Non-fungible Token Standard

https://eips.ethereum.org/EIPS/eip-721

https://github.com/OpenZeppelin/zeppelin-solidity/tree/master/contracts/token/ERC721

ERC721 是以太猫项目采用的合约标准。

7.6.4. ERC827 Token Standard (ERC20 Extension)

https://github.com/ethereum/EIPs/issues/827

https://github.com/OpenZeppelin/zeppelin-solidity/tree/master/contracts/token/ERC827

7.6.5. ERC875 for non fungible tokens and simple atomic swaps

https://github.com/ethereum/EIPs/issues/875

https://github.com/alpha-wallet/ERC875-Example

7.6.6. ERC: Standard URI scheme with metadata, value and byte code

https://gist.github.com/netkiller/427c196eb256ed43c7be08ac875d34a7