代币合约

代币合约

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Coin{
    address public minter;
    mapping(address=>uint) public balances;
    event Sent(address from,address to,uint amount);
    constructor() public{
            minter = msg.sender;
    }
    function mint(address receiver,uint amount) public {
        require(msg.sender == minter);
        balances[receiver] += amount;
    }
    function send(address receiver,uint amount) public {
        require(amount <= balances[msg.sender]);
        balances[msg.sender] -= amount;
        balances[receiver] += amount;
        emit Sent(msg.sender,receiver,amount);
    }
}

1. 说明
   1. mint 铸币
   2. send 转币并没有考虑到uint界限，此处只做简单代币合约的说明
   3. balances 保存各个账户地址的币数
   4. Sent事件（记录，监听）事件是以太坊虚拟机(EVM)日志基础设施提供的一个便利接口。当被发送事件（调用）时，会触发参数存储到交易的日志中（一种区块链上的特殊数据结构）。这些日志与合约的地址关联，并记录到区块链中。
2. 操作
   1. 使用remix进行编译，部署
      
   2. 使用
      

      mint用于手动输入确定自己的代币数并转到自己的账户中

      send用于向其他地址传递代币

      balances用于查询每个地址的代币数

      minter用户确定持有者

3. 改进：确保代币数一定，避免溢出

   // SPDX-License-Identifier: GPL-3.0
   
   pragma solidity >=0.7.0 <0.9.0;
   
   contract Coin{
       mapping(address=>uint) public balances;
       event Sent(address from,address to,uint amount);
       constructor(uint initalSupply) public{
               balances[msg.sender]=initalSupply;
       }
       function send(address receiver,uint amount) public returns (bool success){
           require(amount <= balances[msg.sender]);
           require(balances[receiver] + amount >= balances[receiver]);
           balances[msg.sender] -= amount;
           balances[receiver] += amount;
           emit Sent(msg.sender,receiver,amount);
           return true;
       }
   }
   

4. ERC20标准V神于2015年6月提出此标准，由Fabian Vogelsteller(erc20及erc725作者，也是LUKSO Token 创始人)于2015年11月提交EIP-20。该标准允许开发者在以太坊区块链网络上开发属于自己的代币，该标准定义了开发者可以按照标准要求使用一些简单的功能。ERC20代币标准发行的代币均为同质化代币，与NFT非同质化货币不同。同质化所有代币其价值与属性完全一致，它们之间可以完全等价互换。而非同质化代币NFT则不同，非同质化代币之间不是完全相同的属性，即存在差异，如艺术品，这是非同质化的，存在差异。基于ERC20编写的代币合约例子：

   pragma solidity ^0.4.16;
   contract Token{
       uint256 public totalSupply;
   
       function balanceOf(address _owner) public constant returns (uint256 balance);
       function transfer(address _to, uint256 _value) public returns (bool success);
       function transferFrom(address _from, address _to, uint256 _value) public returns   
       (bool success);
   
       function approve(address _spender, uint256 _value) public returns (bool success);
   
       function allowance(address _owner, address _spender) public constant returns 
       (uint256 remaining);
   
       event Transfer(address indexed _from, address indexed _to, uint256 _value);
       event Approval(address indexed _owner, address indexed _spender, uint256 
       _value);
   }
   
   contract TokenDemo is Token {
   
       string public name;                   //名称，例如"My test token"
       uint8 public decimals;               //返回token使用的小数点后几位。比如如果设置为3，就是支持0.001表示.
       string public symbol;               //token简称,like MTT
   
       function TokenDemo(uint256 _initialAmount, string _tokenName, uint8 _decimalUnits, string _tokenSymbol) public {
           totalSupply = _initialAmount * 10 ** uint256(_decimalUnits);         // 设置初始总量
           balances[msg.sender] = totalSupply; // 初始token数量给予消息发送者，因为是构造函数，所以这里也是合约的创建者
   
           name = _tokenName;                   
           decimals = _decimalUnits;          
           symbol = _tokenSymbol;
       }
   
       function transfer(address _to, uint256 _value) public returns (bool success) {
           //默认totalSupply 不会超过最大值 (2^256 - 1).
           //如果随着时间的推移将会有新的token生成，则可以用下面这句避免溢出的异常
           require(balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]);
           require(_to != 0x0);
           balances[msg.sender] -= _value;//从消息发送者账户中减去token数量_value
           balances[_to] += _value;//往接收账户增加token数量_value
           Transfer(msg.sender, _to, _value);//触发转币交易事件
           return true;
       }
   
       function transferFrom(address _from, address _to, uint256 _value) public returns 
       (bool success) {
           require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value);
           balances[_to] += _value;//接收账户增加token数量_value
           balances[_from] -= _value; //支出账户_from减去token数量_value
           allowed[_from][msg.sender] -= _value;//消息发送者可以从账户_from中转出的数量减少_value
           Transfer(_from, _to, _value);//触发转币交易事件
           return true;
       }
       function balanceOf(address _owner) public constant returns (uint256 balance) {
           return balances[_owner];
       }
   
       function approve(address _spender, uint256 _value) public returns (bool success)   
       { 
           allowed[msg.sender][_spender] = _value;
           Approval(msg.sender, _spender, _value);
           return true;
       }
   
       function allowance(address _owner, address _spender) public constant returns (uint256 remaining) {
           return allowed[_owner][_spender];//允许_spender从_owner中转出的token数
       }
       mapping (address => uint256) balances;
       mapping (address => mapping (address => uint256)) allowed;
   }