blockchain - 在 Solidity 中实现买卖

Question

所以我希望能够买卖代币，但也希望用户能够将 eth 发送到我的合约钱包并接收我的代币作为交换。我相信我已经准备好供买卖双方一起进行交易的代码，但我认为我没有这些代码可以让某人收到发送给我以太坊的代币。我想做到这一点，一开始人们会向我发送 eth，以获得一些设置为基值的代币

pragma solidity 0.4.22;

contract ERC20Basic {

    string public constant name = "Community Token";
    string public constant symbol = "COMM";
    uint8 public constant decimals = 1;  


    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
    event Transfer(address indexed from, address indexed to, uint tokens);


    mapping(address => uint256) balances;

    mapping(address => mapping (address => uint256)) allowed;
    
    uint256 totalSupply_;

    using SafeMath for uint256;


   constructor(uint256 total) public {  
    totalSupply_ = total;
    balances[msg.sender] = totalSupply_;
    }  

    function totalSupply() public view returns (uint256) {
    return totalSupply_;
    }
    
    function balanceOf(address tokenOwner) public view returns (uint) {
        return balances[tokenOwner];
    }

    function transfer(address receiver, uint numTokens) public returns (bool) {
        require(numTokens <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender].sub(numTokens);
        balances[receiver] = balances[receiver].add(numTokens);
        emit Transfer(msg.sender, receiver, numTokens);
        return true;
    }

    function approve(address delegate, uint numTokens) public returns (bool) {
        allowed[msg.sender][delegate] = numTokens;
        emit Approval(msg.sender, delegate, numTokens);
        return true;
    }

    function allowance(address owner, address delegate) public view returns (uint) {
        return allowed[owner][delegate];
    }

    function transferFrom(address owner, address buyer, uint numTokens) public returns (bool) {
        require(numTokens <= balances[owner]);    
        require(numTokens <= allowed[owner][msg.sender]);
    
        balances[owner] = balances[owner].sub(numTokens);
        allowed[owner][msg.sender] = allowed[owner][msg.sender].sub(numTokens);
        balances[buyer] = balances[buyer].add(numTokens);
        emit Transfer(owner, buyer, numTokens);
        return true;
    }
}

library SafeMath { 
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
      assert(b <= a);
      return a - b;
    }
    
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
      uint256 c = a + b;
      assert(c >= a);
      return c;
    }
}

Answer 1

一个非常基本的买卖示例:

pragma solidity ^0.8;

contract ERC20Basic{
    uint256 public constant tokenPrice = 5; // 1 token for 5 wei
    
    function buy(uint256 _amount) external payable {
        // e.g. the buyer wants 100 tokens, needs to send 500 wei
        require(msg.value == _amount * tokenPrice, 'Need to send exact amount of wei');
        
        /*
         * sends the requested amount of tokens
         * from this contract address
         * to the buyer
         */
        transfer(msg.sender, _amount);
    }
    
    function sell(uint256 _amount) external {
        // decrement the token balance of the seller
        balances[msg.sender] -= _amount;
        increment the token balance of this contract
        balances[address(this)] += _amount;

        /*
         * don't forget to emit the transfer event
         * so that external apps can reflect the transfer
         */
        emit Transfer(msg.sender, address(this), _amount);
        
        // e.g. the user is selling 100 tokens, send them 500 wei
        payable(msg.sender).transfer(amount * tokenPrice);
    }
}

这将允许任何用户从您的合约买卖代币。您的合约需要拥有这些代币才能将它们出售给用户。此外，您的合约需要有足够的 ETH 才能从用户那里 repo 代币。

你可以扩展这段代码来实现

• 有权更改价格的契约(Contract)所有者
• 买卖价格不同
• 费用
• 最小/最大金额(每笔交易、每位用户、每天……)
• 根据 msg.value 计算代币数量(用户不必知道确切数量)
• 等...

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请注意，我的代码片段使用的是 Solidity 0.8，其中会自动防止整数溢出。问题是使用已弃用的 Solidity 0.4，因此您需要使用 SafeMath，使用 require/assert 检查值或升级到 Solidity 0.8 以获得相同的结果。