4.2 合约实战-实现标准代币接口这一节我们来看一下以太坊设置的标准的代币接口ERC-20：https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
有了标准之后，例如钱包，交易所，就可以有一个统一的接口来支持所有的代币。- pragma solidity ^0.4.20;contract ERC20Interface{string public name; // 代币的名字string public symbol; // 代币的一个简写uint8 public decimals; // 返回代币的小数点位。最基本单位。uint public totalSupply; // 总供应量function balanceOf(address _owner) view returns (uint256 balance); // 查看余额，必须实现function transfer(address _to, uint256 _value) returns (bool success); // 转账，必须实现function transferFrom(address _from, address _to, uint256 _value) returns (bool success); // 从一个地址，转移到另一个地址function approve(address _spender, uint256 _value) returns (bool success); // 授权某一个地址可操作指定数量的代币function allowance(address _owner, address _spender) view returns (uint256 remaining); // 查看一个地址，可操纵另一个的地址的剩余金额event Transfer(address indexed _from, address indexed _to, uint256 _value); // 转账操作触发的事件event Approval(address indexed _owner, address indexed _spender, uint256 _value); // 授权操作触发的事件}
- pragma solidity ^0.4.20;contract ERC20Interface{string public name;string public symbol;uint8 public decimals;uint public totalSupply;function transfer(address _to, uint256 _value) returns (bool success);function transferFrom(address _from, address _to, uint256 _value) returns (bool success);function approve(address _spender, uint256 _value) returns (bool success);function allowance(address _owner, address _spender) view returns (uint256 remaining);event Transfer(address indexed _from, address indexed _to, uint256 _value);event Approval(address indexed _owner, address indexed _spender, uint256 _value);}contract ERC20 is ERC20Interface{mapping (address => uint256) public balanceOf;// 这个映射用来保存一个账户被其他账号授权可操作的代币余额mapping (address => mapping (address => uint256)) internal allowed;constructor() public{name = "GWF FIRST TOKEN";symbol = "XIANGSHI";decimals = 0;totalSupply = 10000;balanceOf[msg.sender] = totalSupply;}function transfer(address _to, uint256 _value) returns (bool success){require(_to != address(0));require(balanceOf[msg.sender] >= _value);require(balanceOf[_to] + _value >= balanceOf[_to]);balanceOf[msg.sender] -= _value;balanceOf[_to] += _value;emit Transfer(msg.sender, _to, _value);}function transferFrom(address _from, address _to, uint256 _value) returns (bool success){require(_to != address(0));require(balanceOf[_from] >= _value);require(allowed[_from][msg.sender] >= _value);require(balanceOf[_to] + _value >= balanceOf[_to]);balanceOf[_from] -= _value;balanceOf[_to] += _value;emit Transfer(msg.sender, _to, _value);success = true;}function approve(address _spender, uint256 _value) returns (bool success){allowed[msg.sender][_spender] = _value;emit Approval(msg.sender, _spender, _value);success = true;}function allowance(address _owner, address _spender) view returns (uint256 remaining){return allowed[_owner][_spender];}event Transfer(address indexed _from, address indexed _to, uint256 _value);event Approval(address indexed _owner, address indexed _spender, uint256 _value);}
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