以太坊代币标准ERC20、ERC165、ERC721

两个概念

• ERC(Ethereum Request for Comment) 以太坊意见征集稿
• EIP(Ethereum Improvement Proposals)以太坊改进提案

ERC和EIP用于使得以太坊更加完善；在ERC中提出了很多标准，用的最多的标准就是它的Token标准;
有哪些标准详细见https://eips.ethereum.org/erc

常见ERC标准

ERC-20	Token Standard
ERC-721	Non-Fungible Token Standard
ERC-165	Standard Interface Detection
ERC-777	Token Standard
ERC-1155	Multi Token Standard

ERC-20

主要是指同质化代币标准（不同人持有的一个代币是等值的）。
ERC-20标准中主要有6个函数和两个事件

其中这6个函数表达的意义是：
totalSupply：总发行量
balanceOf：账户余额
transfer：转账
transferFrom：针对授权进行转账
approve：授权
allowance：owner授权给spender余额
具体的详细见https://eips.ethereum.org/EIPS/eip-20

实现ERC20标准代币

想要发现ERC20标准的代币，就需要实现ERC20标准接口中的函数

先写ERC20标准接口

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;interface IERC20 {function name() external  view returns (string memory);function symbol() external view returns (string memory);function decimals() external view returns (uint8);function totalSupply() external view returns (uint256);function balanceOf(address _owner) external view returns (uint256 balance);function transfer(address _to, uint256 _value) external returns (bool success);function transferFrom(address _from, address _to, uint256 _value) external returns (bool success);function approve(address _spender, uint256 _value) external returns (bool success);function allowance(address _owner, address _spender) external view returns (uint256 remaining);//_from和_to两个参数有indexed关键字修饰，表示这些参数可以作为过滤条件来搜索事件。event Transfer(address indexed _from, address indexed _to, uint256 _value);event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

再实现ERC20标准代币

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;import "./IERC20.sol";contract ERC20 is IERC20{string ercName;string ercSymbol;uint8 ercDecimals;uint256 ercTotalSupply;mapping(address=>uint256) ercBalances;//一个人可以有多个委托人：授权者=>被授权者=>授权金额mapping (address=>mapping (address=>uint256)) ercAllowance;//合约部署者address public owner;constructor(string memory _name, string memory _symbol,uint8 _decimals){ercName=_name;ercSymbol=_symbol;ercDecimals=_decimals;owner=msg.sender;}//token名称function name() override  external  view returns (string memory){return ercName;}//token符号function symbol() override external view returns (string memory){return ercSymbol;}//token可以拆分到的精度function decimals() override external view returns (uint8){return ercDecimals;}//token发行总量function totalSupply() override external view returns (uint256){return ercTotalSupply;}//账户余额function balanceOf(address _owner) override external view returns (uint256 balance){return ercBalances[_owner];}//给某人转账function transfer(address _to, uint256 _value) override external returns (bool success){require(_value>0,"_value must >0");require(_to!=address(0),"_to is null");require(ercBalances[msg.sender]>=_value,"user's balance not enough");ercBalances[msg.sender]-=_value;ercBalances[_to]+=_value;emit Transfer(msg.sender, _to, _value);return true;}//被授权用户用我的token转账;_from: 授权者，_to:转给谁function transferFrom(address _from, address _to, uint256 _value) override external returns (bool success){require(ercBalances[_from] >= _value,"user's balance not enough");require(ercAllowance[_from][msg.sender]>=_value,"approve's balance not enough");require(_value>0,"_value must > 0");require(_to!=address(0),"_to is null");ercBalances[_from]-=_value;ercBalances[_to]+=_value;ercAllowance[_from][msg.sender]-=_value;emit Transfer(_from, _to, _value);return true;}//授权其他用户可以花费我多少tokenfunction approve(address _spender, uint256 _value) override external returns (bool success){// require(_value>0,"value must >0");//让_value可以等于0，当其为0时表示收回授权require(_spender!=address(0),"_spender can not be null");require(ercBalances[msg.sender]>=_value,"user's balance not enough");ercAllowance[msg.sender][_spender]=_value; emit Approval(msg.sender, _spender, _value);return true;}//获取授花费的余额tokenfunction allowance(address _owner, address _spender) override external view returns (uint256 remaining){return ercAllowance[_owner][_spender];}//代币发行机制function mint(address _to,uint256 _value) public{require(msg.sender==owner,"only owner can mint");require(_value>0,"_value must > 0");require(_to!=address(0),"_to is invalid"); ercBalances[_to]+=_value;ercTotalSupply+=_value;emit Transfer(address(0), _to, _value);}
}

ERC165

是一个标准接口检测的标准；用于检测合约是否符合规范

注意：函数选择器：
函数参数只保留类型，计算 hash("函数名(类型1, 类型2, ...)")，并取哈希结果的前4个字节
举例，如下函数的函数选择器是：计算hash(“Transfer(address,uint256)”)，并取哈希结果的前4个字节

function Transfer(address to,uint256 value){//函数体
}

注意：接口ID:
将一个接口里面的所有函数选择器做异或处理，得到接口的ID

如何判断一个接口支持了ERC165?

ERC-721

主要是指非同质化代币标准（不同人持有的一个代币的价值不一样，如，艺术品）