solidity实战练习2--ERC20实现

//SPDX-License-Identifier:MTT
pragma solidity ^0.8.24;
 
interface erc20{
    function name()external view returns (string memory);//查看代币的名称
    function symbol() external view returns(string memory);//查看代币简称
    function totalSupply()external view returns(uint);//查看代币的总供应量
    function decimal()external view returns(uint8);//查看代币的精度
    function balanceOf(address account)external view returns(uint);//查看某账户的余额
 
    function transfer(address recipient ,uint amount) external payable returns(bool);//合约的调用者向某地址发送代币
    function approve(address spender ,uint amount) external returns(bool);//合约调用者向某一地址指定代币数量
    function allowance(address owner,address spender) external view returns(uint);//查看转账授权的金额
    function transferDirect(address _form,address _to,uint amount) external returns(bool);//直接执行转账操作
    function transferByApproves(address _to,uint amount) external returns(bool);//通过approve执行转账操作
}
 
contract erc20tokens{//定义需要的状态变量
        string public  _name;
        string public _symbol;
        uint public _totalSupply;
        uint8 public  _decimal;
        mapping(address=>uint)public balances;
        mapping(address=>mapping(address=>uint)) public approves;
        constructor(//给状态变量进行赋值操作，在构造函数里面赋值时候仅仅会进行一次
            string memory _name_,
            string memory _symbol_,
            uint _totalSupply_,
            uint8 _decimal_
        ) {
            _name=_name_;
            _symbol=_symbol_;
            _totalSupply =_totalSupply_;
            _decimal=_decimal_;
        }
        event Transfer(address _from,address _to,uint amount);//定义事件，记录转账操作
        event Approves(address _from,address _to,uint amount);//定义事件，记录授权操作，以及授权的余额
 
//实现interface接口的函数
    function name()external view returns (string memory)//查看代币的名称
    {
        return _name;
    }
    function symbol() external view returns(string memory)//查看代币简称
    {
        return _symbol;
    }
    function totalSupply()external view returns(uint)//查看代币的总供应量
    {
        return _totalSupply;
    }
    function decimal()external view returns(uint8)//查看代币的精度
    {
        return _decimal;
 
    }
    function balanceOf(address account)external view returns(uint)//查看某账户的余额
    {
        return balances[account];
    }
 
    function transfer(address recipient ,uint amount) external  returns(bool)//合约的调用者向某地址发送代币
    {
        require (balances[msg.sender]<=amount,"Sorry,you have no enough amount to send");
        return _transfer(msg.sender,recipient,amount);
    }
 
 
    function approve(address spender ,uint amount) external returns(bool)//合约调用者向某一地址授权指定数量代币
    {
        require(approves[msg.sender][spender]==0,"reapproved");
        approves[msg.sender][spender]=amount;
        return true;
 
    }
    function allowance(address owner,address spender) external view returns(uint)//查看转账授权的金额
    {
        return approves[owner][spender];
    }
    function transferByApproves(address _to,uint amount) internal returns(bool)
    {
        address _from=msg.sender;
        require(approves[_from][_to]>=amount,"You hava no right to send too much");
        emit Approves(_from,_to,amount);
        approves[_from][_to]-=amount;
        return _transfer(_from,_to,amount);
    }
    function transferDirect(address _from,address _to,uint amount) external returns(bool)//执行转账操作
    {
        require(balances[_from]>=amount,"You have no enough monay");
        return _transfer(_from,_to,amount);
 
    }
    function _transfer(address _from,address _to,uint amount) internal  returns (bool)//转账操作集成于_transfer函数，通过其他需要用到转账的函数只需要通过调用_transfer函数就可以
    {
        require(balances[_from]>=amount,"Sorry, the amount is too low");//只要调用_transfer 函数就会触发事件
        balances[_from]-=amount;
        balances[_to]+=amount;
        emit Transfer(_from,_to,amount);
        return true;
    }
}

ps:
授权转账的主要用途包括：

• 代理转账：允许另一个地址代表你进行转账操作，这在复杂的合约交互中特别有用。例如，允许某个合约在你的代币余额中进行交易，而无需事先将代币转移到合约地址。

• 限制额度：通过 approve 函数授权一个特定的地址可以转移的代币数量，可以帮助减少合约中的风险，因为授权的数量通常是有限的。

• 灵活性：授权机制允许你动态地管理你的资金，可以随时修改授权的地址和数量，这为复杂的合约逻辑提供了更大的灵活性和安全性。