ERC20代币标准怎么实现

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pragma solidity ^0.4.20;// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.mdcontract NanToken {    //Token    //Methods    //NOTE: Callers MUST handle false from returns (bool success). Callers MUST NOT assume that false is never returned!    // 所有 returns (bool success) 的方法，都要考虑返回false的逻辑；    //name    //Returns the name of the token - e.g. "MyToken".    //    //OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.    function name() view returns (string name);    //symbol    //Returns the symbol of the token.E.g. "HIX".    //    //OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.    function symbol() view returns (string symbol);    //decimals    //Returns the number of decimals the token uses - e.g. 8, means to divide the token amount by 100000000 to get its user representation.    //    //OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.    // 精度    function decimals() view returns (uint8 decimals);    //totalSupply    //Returns the total token supply.    function totalSupply() view returns (uint256 totalSupply);    //balanceOf    //Returns the account balance of another account with address _owner.    // 总量    function balanceOf(address _owner) view returns (uint256 balance);    //transfer    //Transfers _value amount of tokens to address _to, and MUST fire the Transfer event. The function SHOULD throw if the _from account balance does not have enough tokens to spend.    //    //Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.    // 从当前地址转指定量到指定地址    // 若当前地址没有足够的余额，应该抛出异常    // 每次调用成功，哪怕数量是0，都必须触发 Transfer 事件；    function transfer(address _to, uint256 _value) returns (bool success);    //transferFrom    //Transfers _value amount of tokens from address _from to address _to, and MUST fire the Transfer event.    //    //The transferFrom method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf. This can be used for example to allow a contract to transfer tokens on your behalf and / or to charge fees in sub- currencies. The function SHOULD throw unless the _from account has deliberately authorized the sender of the message via some mechanism.    //    //Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.    // 用于提币逻辑；    // 每次调用成功必须触发 Transfer 事件；哪怕数量是0；    function transferFrom(address _from, address _to, uint256 _value) returns (bool success);    //approve    //Allows _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.    //    //NOTE : To prevent attack vectors like the one described here[https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh5DYKjA_jp-RLM/] and discussed here[https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729], clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to 0 before setting it to another value for the same spender. THOUGH The contract itself shouldn't enforce it, to allow backwards compatibility with contracts deployed before    // 允许指定的地址 分一次或多次从当前地址提币；若再次调用此方法，则重置数量    // 为避免攻击，客户端实现时应该先向某地址设置数量为0，再给相同的地址设置数量为 实际的数量；    // 这为了向后兼容之前部署的合约,虽然不是强制要求    function approve(address _spender, uint256 _value) returns (bool success);    //allowance    //Returns the amount which _spender is still allowed to withdraw from _owner.    // 查询 owner 授权给 spender 的剩余提币数量    function allowance(address _owner, address _spender) view returns (uint256 remaining);    //Events    //Transfer    //MUST trigger when tokens are transferred, including zero value transfers.    //    //A token contract which creates new tokens SHOULD trigger a Transfer event with the _from address set to 0x0 when tokens are created.    // token 被 成功 transfer 后，需要触发Transfer 事件，哪怕数量为0；    // 当创建一个新的token后，应该触发Transfer 事件，    event Transfer(address indexed _from, address indexed _to, uint256 _value);    //Approval    //MUST trigger on any successful call to approve(address _spender, uint256 _value).    // 每次approve方法被成功调用后，都必须触发 Approval事件；    event Approval(address indexed _owner, address indexed _spender, uint256 _value)};}

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