在区块链的世界里,以太坊（Ethereum）无疑是最具影响力的智能合约平台之一，而ERC20（Ethereum Request for Comments 20）标准，则是以太坊上应用最广泛、最成熟的代币标准，它像一套通用的“语法规则”，使得不同代币能够在以太坊生态中无缝交互，被钱包识别、在交易所交易、用于DeFi协议等，本文将带您深入了解以太坊ERC20代币合约的代码结构、核心功能以及如何编写一个基本的ERC20代币。
ERC20不是一个具体的代币,而是一套技术标准，任何遵循ERC20标准的代币合约，都必须实现一组预定义的接口（Interface）和事件（Event），这确保了所有ERC20代币都具有一致的行为方式，
一个标准的ERC20代币合约通常使用Solidity语言编写,继承自ERC20接口或直接实现其所有方法，下面我们通过一个简化版的ERC20合约代码来解析其核心组成部分。
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
/**ERC20接口
* @dev 见 https://eips.ethereum.org/EIPS/eip-20
*/
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function transfer(address recipient, uint256 amount) external returns (bool);
function allowance(address owner, address spender) external view returns (uint256);
function approve(address spender, uint256 amount) external returns (bool);
function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);
}
/**简化版ERC20代币合约
*/
contract MyToken is IERC20 {
// 1. 状态变量
string private _name;
string private _symbol;
uint8 private _decimals;
uint256 private _totalSupply;
mapping(address => uint256) private _balances; // 地址到余额的映射
mapping(address => mapping(address => uint256)) private _allowances; // 授权映射
// 2. 构造函数
constructor(string memory name_, string memory symbol_, uint8 decimals_) {
_name = name_;
_symbol = symbol_;
_decimals = decimals_;
// 初始供应量，10亿代币，18位小数，即 1,000,000,000 * 10^18
uint256 initialSupply = 1000000000 * (10 ** uint256(decimals_));
_totalSupply = initialSupply;
_balances[msg.sender] = initialSupply; // 将初始供应量分配给合约部署者
emit Transfer(address(0), msg.sender, initialSupply); // 触发Transfer事件，从零地址（创世）转移到部署者
}
// 3. 实现IERC20接口的方法
/**
* @dev 返回代币名称
*/
function name() public view override returns (string memory) {
return _name;
}
/**
* @dev 返回代币符号
*/
function symbol() public view override returns (string memory) {
return _symbol;
}
/**
* @dev 返回代币小数位数
*/
function decimals() public view override returns (uint8) {
return _decimals;
}
/**
* @dev 返回代币总供应量
*/
function totalSupply() public view override returns (uint256) {
return _totalSupply;
}
/**
* @dev 返回账户的代币余额
*/
function balanceOf(address account) public view override returns (uint256) {
return _balances[account];
}
/**
* @dev 转账代币
*/
function transfer(address recipient, uint256 amount) public override returns (bool) {
_transfer(msg.sender, recipient, amount);
return true;
}
/**
* @dev 授权某个地址可以花费你的代币
*/
function approve(address spender, uint256 amount) public override returns (bool) {
_approve(msg.sender, spender, amount);
return true;
}
/**
* @dev 从授权地址转账代币
*/
function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
_transfer(sender, recipient, amount);
uint256 currentAllowance = _allowances[sender][msg.sender];
require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
_approve(sender, msg.sender, currentAllowance - amount);
return true;
}
/**
* @dev 返回授权额度
*/
function allowance(address owner, address spender) public view override returns (uint256) {
return _allowances[owner][spender];
}
// 4. 内部函数（Internal Functions） - 实现核心逻辑，避免代码重复
/**
* @dev 内部转账函数
*/
function _transfer(address sender, address recipient, uint256 amount) internal {
require(sender != address(0), "ERC20: transfer from the zero address");
require(recipient != address(0), "ERC20: transfer to the zero address");
require(_balances[sender] >= amount, "ERC20: transfer amount exceeds balance");
_balances[sender] -= amount;
_balances[recipient] += amount;
emit Transfer(sender, recipient, amount);
}
/**
* @dev 内部授权函数
*/
function _approve(address owner, address spender, uint256 amount) internal {
require(owner != address(0), "ERC20: approve from the zero address");
require(spender != address(0), "ERC20: approve to the zero address");
_allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);
}
}
接口（Interface）IERC20：
contract MyToken is IERC20来声明遵循此接口。状态变量（State Variables）：
_name, _symbol, _decimals：存储代币的基本信息。_totalSupply：记录代币的总供应量。_balances：是一个mapping（键值对映射），用于存储每个地址对应的代币余额。_allowances：是一个二维mapping，用于存储owner地址授权给spender地址的代币花费额度。构造函数（Constructor）：
msg.sender），并触发一个Transfer事件，记录从“零地址”（代表创世）到部署者的代币创建过程。核心接口方法实现：
name(), symbol(), decimals(), totalSupply(), balanceOf()：这些是查询函数，使用view修饰符，表示它们只读取状态变量而不修改状态，因此不会消耗Gas（除了在交易中调用时）。transfer(recipient, amount)：允许代币持有者向recipient地址转移amount数量的代币，它内部调用_transfer来完成实际逻辑。approve(spender, amount)：允许代币持有者授权spender地址可以花费其最多amount数量的代币，它内部调用_approve。transferFrom(sender, recipient, amount)：允许被授权的spender（即调用此方法的msg.sender）从sender地址向recipient地址转移amount数量的代币，它会先检查授权额度，然后调用_transfer，并更新授权额度。友情链接：
