知乎专栏 | 多维度架构 |
https://theethereum.wiki/w/index.php/ERC20_Token_Standard
ERC20 “描述了实现代币合约的标准功能”,ERC20 是各个代币的标准接口。ERC20 代币仅仅是以太坊代币的子集。为了充分兼容 ERC20,开发者需要将一组特定的函数集成到他们的智能合约中,以便在高层面能够执行以下操作:
ERC20 提供的方法
获得代币总供应量
获得账户余额
转让代币
批准花费代币
原合约
pragma solidity ^0.4.21; contract NetkillerToken { address public owner; string public name; string public symbol; uint public decimals; uint256 public totalSupply; event Transfer(address indexed from, address indexed to, uint256 value); /* This creates an array with all balances */ mapping (address => uint256) public balanceOf; function NetkillerToken(uint256 initialSupply, string tokenName, string tokenSymbol, uint decimalUnits) public { owner = msg.sender; name = tokenName; symbol = tokenSymbol; decimals = decimalUnits; totalSupply = initialSupply * 10 ** uint256(decimals); balanceOf[msg.sender] = totalSupply; } /* Send coins */ function transfer(address _to, uint256 _value) public { /* Check if the sender has balance and for overflows */ require(balanceOf[msg.sender] >= _value && balanceOf[_to] + _value >= balanceOf[_to]); /* Add and subtract new balances */ balanceOf[msg.sender] -= _value; balanceOf[_to] += _value; /* Notify anyone listening that this transfer took place */ emit Transfer(msg.sender, _to, _value); } }
新版合约
pragma solidity ^0.4.24; contract NetkillerToken { address public owner; string public name; string public symbol; uint public decimals; uint256 public totalSupply; event Transfer(address indexed from, address indexed to, uint256 value); /* This creates an array with all balances */ mapping (address => uint256) public balanceOf; constructor(uint256 initialSupply, string tokenName, string tokenSymbol, uint decimalUnits) public { owner = msg.sender; name = tokenName; symbol = tokenSymbol; decimals = decimalUnits; totalSupply = initialSupply * 10 ** uint256(decimals); balanceOf[msg.sender] = totalSupply; } /* Send coins */ function transfer(address _to, uint256 _value) public { /* Check if the sender has balance and for overflows */ require(balanceOf[msg.sender] >= _value && balanceOf[_to] + _value >= balanceOf[_to]); /* Add and subtract new balances */ balanceOf[msg.sender] -= _value; balanceOf[_to] += _value; /* Notify anyone listening that this transfer took place */ emit Transfer(msg.sender, _to, _value); } }
所有的ERC20代币都是按照下面这些方法来定义的。下面我们讲解一下每个方法的作用。
function name() view public returns (string name)
返回string类型的ERC20代币的名字,例如:Netkiller Reader Coin
function symbol() view public returns (string symbol)
返回string类型的ERC20代币的符号,也就是代币的简称,例如:NRC。
function decimals() view public returns (uint decimals)
支持几位小数点后几位。如果设置为3。也就是支持0.001表示。
function totalSupply() view public returns (uint256 totalSupply)
发行代币的总量,可以通过这个函数来获取。所有智能合约发行的代币总量是一定的,totalSupply必须设置初始值。
function balanceOf(address _owner) public returns (uint256 balance)
输入地址,可以获取该地址代币的余额。
function transfer(address _to, uint256 _value) public returns (bool success)
调用transfer函数将自己的token转账给_to地址,_value为转账金额
function approve(address _spender, uint256 _value) public returns (bool success)
批准_spender账户从自己的账户转移_value个token。可以分多次转移。
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
与approve搭配使用,approve批准之后,调用transferFrom函数来转移token。
function allowance(address _owner, address _spender) public returns (uint256 remaining)
返回_spender还能提取token的个数。
approve、transferFrom及allowance解释:账户A有1000个代币,想允许B账户随意调用100个代币。A账户按照以下形式调用approve函数approve(B,100)。当B账户想用这100个代币中的10个代币给C账户时,则调用transferFrom(A, C, 10)。这时调用allowance(A, B)可以查看B账户还能够调用A账户多少个token。