如何写个众筹合约

编写众筹合约涉及使用 Solidity 语言来定义智能合约。以下是一个简单的众筹合约示例，基于以太坊的 ERC-20 代币标准。请注意，这只是一个基础示例，实际应用中可能需要更多的安全性和功能。

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

import “@openzeppelin/contracts/token/ERC20/IERC20.sol”;

contract Crowdfunding {
address public owner;
IERC20 public token; // 使用的代币合约地址
uint256 public goal; // 众筹目标
uint256 public deadline; // 截止日期
uint256 public raisedAmount; // 已筹集金额
mapping(address => uint256) public contributions; // 参与者的贡献记录
bool public fundingGoalReached = false; // 众筹目标是否达成
bool public crowdsaleClosed = false; // 众筹是否关闭

event Contribution(address indexed contributor, uint256 amount);
event FundingGoalReached(uint256 amountRaised);
event CrowdsaleClosed();

modifier onlyOwner() {
require(msg.sender == owner, “Only the owner can call this function”);
_;
}

modifier notClosed() {
require(!crowdsaleClosed, “Crowdsale is closed”);
_;
}

modifier afterDeadline() {
require(block.timestamp >= deadline, “Crowdsale deadline has not passed”);
_;
}

constructor(
address _token,
uint256 _goal,
uint256 _durationInMinutes
) {
owner = msg.sender;
token = IERC20(_token);
goal = _goal;
deadline = block.timestamp + _durationInMinutes * 1 minutes;
}

function contribute(uint256 _amount) external notClosed {
require(block.timestamp < deadline, "Crowdsale has ended");
require(raisedAmount + _amount <= goal, "Contribution exceeds the goal");

token.transferFrom(msg.sender, address(this), _amount);
contributions[msg.sender] += _amount;
raisedAmount += _amount;

emit Contribution(msg.sender, _amount);

if (raisedAmount >= goal) {
fundingGoalReached = true;
emit FundingGoalReached(raisedAmount);
}
}

function withdraw() external afterDeadline {
require(fundingGoalReached, “Funding goal not reached”);
uint256 amount = contributions[msg.sender];
contributions[msg.sender] = 0;
token.transfer(msg.sender, amount);
}

function closeCrowdsale() external onlyOwner {
require(!crowdsaleClosed, “Crowdsale already closed”);
crowdsaleClosed = true;
emit CrowdsaleClosed();
}
}
“`

上述合约使用了 OpenZeppelin 的 ERC20 合约库，确保了在代币交互方面的安全性。在实际使用中，你需要引入相关的库文件，可以通过 [OpenZeppelin GitHub](https://github.com/OpenZeppelin/openzeppelin-contracts) 获取。

此众筹合约支持以下功能：

1. 设置众筹目标、截止日期和代币。
2. 参与者可以通过 `contribute` 函数贡献代币。
3. 在达到众筹目标后，参与者可以通过 `withdraw` 函数提取代币。
4. 合约拥有者可以通过 `closeCrowdsale` 函数关闭众筹。

请确保在实际使用前仔细测试和审查合约，以确保其符合项目需求并且安全可靠。

具体可以参照下面的合约适当修改，仅供学习参考。

// SPDX-License-Identifier: MITpragma solidity ^0.8.0;import "@openzeppelin/contracts/token/ERC20/IERC20.sol";contract Crowdfunding {address public owner;IERC20 public token; // 使用的代币合约地址uint256 public goal; // 众筹目标uint256 public deadline; // 截止日期uint256 public raisedAmount; // 已筹集金额mapping(address => uint256) public contributions; // 参与者的贡献记录bool public fundingGoalReached = false; // 众筹目标是否达成bool public crowdsaleClosed = false; // 众筹是否关闭event Contribution(address indexed contributor, uint256 amount);event FundingGoalReached(uint256 amountRaised);event CrowdsaleClosed();modifier onlyOwner() {require(msg.sender == owner, "Only the owner can call this function");_;}modifier notClosed() {require(!crowdsaleClosed, "Crowdsale is closed");_;}modifier afterDeadline() {require(block.timestamp >= deadline, "Crowdsale deadline has not passed");_;}constructor(address _token,uint256 _goal,uint256 _durationInMinutes) {owner = msg.sender;token = IERC20(_token);goal = _goal;deadline = block.timestamp + _durationInMinutes * 1 minutes;}function contribute(uint256 _amount) external notClosed {require(block.timestamp < deadline, "Crowdsale has ended");require(raisedAmount + _amount = goal) {fundingGoalReached = true;emit FundingGoalReached(raisedAmount);}}function withdraw() external afterDeadline {require(fundingGoalReached, "Funding goal not reached");uint256 amount = contributions[msg.sender];contributions[msg.sender] = 0;token.transfer(msg.sender, amount);}function closeCrowdsale() external onlyOwner {require(!crowdsaleClosed, "Crowdsale already closed");crowdsaleClosed = true;emit CrowdsaleClosed();}}