ERC20 代币合约

ERC20 是以太坊上一种广泛采用的代币标准，它定义了一组标准的接口，用于发行和管理代币。以下是一个简单的 ERC20 代币合约示例，使用 Solidity 编写：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

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);
}

contract ERC20Token is IERC20 {
    string public constant name = "MyToken";
    string public constant symbol = "MTK";
    uint8 public constant decimals = 18;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 private _totalSupply;

    constructor(uint256 initialSupply) {
        _mint(msg.sender, initialSupply);
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public override returns (bool) {
        require(_balances[msg.sender] >= amount, "ERC20: transfer amount exceeds balance");
        _balances[msg.sender] -= amount;
        _balances[recipient] += amount;
        emit Transfer(msg.sender, recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) public view override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        _allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
        require(_balances[sender] >= amount, "ERC20: transfer amount exceeds balance");
        require(_allowances[sender][msg.sender] >= amount, "ERC20: transfer amount exceeds allowance");
        _balances[sender] -= amount;
        _balances[recipient] += amount;
        _allowances[sender][msg.sender] -= amount;
        emit Transfer(sender, recipient, amount);
        return true;
    }

    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");
        _totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);
    }
}

这个合约实现了 ERC20 标准的主要功能：

• totalSupply 返回代币的总供应量。
• balanceOf 返回特定账户的代币余额。
• transfer 允许账户将代币转移给另一个账户。
• approve 允许某个账户（spender）代表另一个账户（owner）转移最多特定数量的代币。
• allowance 返回一个账户（owner）授权给另一个账户（spender）转移代币的数量。
• transferFrom 允许预先授权的账户（spender）代表另一个账户（owner）转移代币。

此外，合约中还有两个事件Transfer和Approval，它们在转移代币和授权操作时被触发，以便区块链上的监听者能够得到通知。

请注意，这个合约只是一个示例，并没有包含安全检查（如SafeMath库以防止溢出），在生产环境中部署合约前，应进行全面的测试和代码审计。