货币是用来交换、偿还债务的媒介。古代货币为金、银、贝壳等实物。现代中央银行发行的纸币等。相对于古代的一般等价物而言
现在的货币本质上是由政府信用的背书。其本身并没有价值。 同理、比特币与以太币本身并没有价值，但是依托于区块链网络的特性，使得其拥有货币的完美属性。包括：
·便携
·耐用
·可分割
·可识别
·可替代
·稀缺且难以仿冒
如下是一段简单的代币代码。balanceOf映射表存储金额。构造函数，定义了初始化发行与管理者。 transfer函数定义了转账操作。完成了货币存储与转移的功能。 本质上，此货币就是存储在balanceOf映射表中的数字。数字本身并没有价值，只有当你认为他有价值的时候，它才会有价值。所以，数字货币的背后，常常是对应与一定的商业价值。例如公司的股权等。
1234567891011121314151617 | pragma solidity ^0.4.23;contract tokenDemo{ mapping(address=>uint) public balanceOf; address owner; constructor(uint initSupply) public { balanceOf[msg.sender] = initSupply; owner = msg.sender; } function transfer(address _to,uint _value) public { balanceOf[owner] -= _value; balanceOf[_to] += _value; }} |
如上面写好的简单代币demo，有三种缺陷。
1、没有权限的控制，任何人都可以调用transfer进行转账
2、没有防止溢出***
3、功能有限
4、没有统一的规范。
想象一下，如果每一个人或企业都写一个属于自己的代币合约。每一个合约都有自己的查询资金的函数名。都有自己的转账的函数名。那么每一次当我们需要用到其他人的代币，都需要查询，此代币合约中，每一个函数的功能。大大降低了效率。
这就为我们引出了ERC20代币。
ERC是以太坊征求意见( Ethereum Request for Comment-20)的缩写. 20代表它的序号。其规范了代币合约，也就意味着，一旦合约满足了ERC20代币的规范，那么其必然有规范的函数标准。如下，就是ERC20代币协议规定的不同的函数及其功能。ERC20协议只是定义了函数的定义与功能，需要代币设计者自定义的实现函数功能。
1234567891011121314151617 | interface ERC20Interface { //总发行数量 function totalSupply() external returns (uint); //查询数量 function balanceOf(address tokenOwner) external returns (uint balance); //查询授权数量 function allowance(address tokenOwner, address spender) external returns (uint remaining); //转账 function transfer(address to, uint tokens) external returns (bool success); //授权 function approve(address spender, uint tokens) external returns (bool success); //授权转账 function transferFrom(address from, address to, uint tokens) external returns (bool success); event Transfer(address indexed from, address indexed to, uint tokens); event Approval(address indexed tokenOwner, address indexed spender, uint tokens);} |
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198 | pragma solidity ^0.4.18;// ----------------------------------------------------------------------------// '' token contract//// 部署地址 :// 标志 : LOVE// 名字 : LOVE TOKEN// 总供应量 100000000000000000000000000// 精度 : 18// ---------------------------------------------------------------------------// ----------------------------------------------------------------------------// SafeMath安全库// ----------------------------------------------------------------------------contract SafeMath { function safeAdd(uint a, uint b) public pure returns (uint c) { c = a + b; require(c >= a); } function safeSub(uint a, uint b) public pure returns (uint c) { require(b <= a); c = a - b; } function safeMul(uint a, uint b) public pure returns (uint c) { c = a * b; require(a == 0 || c / a == b); } function safeDiv(uint a, uint b) public pure returns (uint c) { require(b > 0); c = a / b; }}// ----------------------------------------------------------------------------// ERC20 代币标准// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md// ----------------------------------------------------------------------------contract ERC20Interface { //总发行数量 function totalSupply() public constant returns (uint); //查询数量 function balanceOf(address tokenOwner) public constant returns (uint balance); //查询授权数量 function allowance(address tokenOwner, address spender) public constant returns (uint remaining); //转账 function transfer(address to, uint tokens) public returns (bool success); //授权 function approve(address spender, uint tokens) public returns (bool success); //授权转账 function transferFrom(address from, address to, uint tokens) public returns (bool success); event Transfer(address indexed from, address indexed to, uint tokens); event Approval(address indexed tokenOwner, address indexed spender, uint tokens);}// ----------------------------------------------------------------------------// 所有者合约// ----------------------------------------------------------------------------contract Owned { address public owner; address public newOwner; event OwnershipTransferred(address indexed _from, address indexed _to); function Owned() public { owner = msg.sender; } modifier onlyOwner { require(msg.sender == owner); _; } function transferOwnership(address _newOwner) public onlyOwner { newOwner = _newOwner; } function acceptOwnership() public { require(msg.sender == newOwner); OwnershipTransferred(owner, newOwner); owner = newOwner; newOwner = address(0); }}// ----------------------------------------------------------------------------// ERC20代币，增加标志、名字、精度// 代币转移// ----------------------------------------------------------------------------contract LOVEToken is ERC20Interface, Owned, SafeMath { string public symbol; string public name; uint8 public decimals; uint public _totalSupply; mapping(address => uint) balances; mapping(address => mapping(address => uint)) allowed; // ------------------------------------------------------------------------ // 构造函数 // ------------------------------------------------------------------------ function LOVEToken() public { symbol = "LOVER"; name = "LOVER Token"; decimals = 18; _totalSupply = 100000000000000000000000000; balances[0x6AFe57C1F589C4744ab9FF4ac8899080695a6f5e] = _totalSupply; Transfer(address(0), 0x6AFe57C1F589C4744ab9FF4ac8899080695a6f5e, _totalSupply); } // ------------------------------------------------------------------------ // 总供应量 // ------------------------------------------------------------------------ function totalSupply() public constant returns (uint) { return _totalSupply - balances[address(0)]; } // ------------------------------------------------------------------------ // 得到资金的数量 // ------------------------------------------------------------------------ function balanceOf(address tokenOwner) public constant returns (uint balance) { return balances[tokenOwner]; } // ------------------------------------------------------------------------ // 转账从代币拥有者的账户到其他账户 // - 所有者的账户必须有充足的资金去转账 // - 0值的转账也是被允许的 // ------------------------------------------------------------------------ function transfer(address to, uint tokens) public returns (bool success) { balances[msg.sender] = safeSub(balances[msg.sender], tokens); balances[to] = safeAdd(balances[to], tokens); Transfer(msg.sender, to, tokens); return true; } // ------------------------------------------------------------------------ // 授权 // ------------------------------------------------------------------------ function approve(address spender, uint tokens) public returns (bool success) { allowed[msg.sender][spender] = tokens; Approval(msg.sender, spender, tokens); return true; } // ------------------------------------------------------------------------ // 和approve连接在一起 // // The calling account must already have sufficient tokens approve(...)-d // for spending from the from account and // - From account must have sufficient balance to transfer // - Spender must have sufficient allowance to transfer // - 0 value transfers are allowed // ------------------------------------------------------------------------ function transferFrom(address from, address to, uint tokens) public returns (bool success) { balances[from] = safeSub(balances[from], tokens); allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens); balances[to] = safeAdd(balances[to], tokens); Transfer(from, to, tokens); return true; } // ------------------------------------------------------------------------ // 返回授权数量 // ------------------------------------------------------------------------ function allowance(address tokenOwner, address spender) public constant returns (uint remaining) { return allowed[tokenOwner][spender]; } // ------------------------------------------------------------------------ // 合约不接受以太币 // ------------------------------------------------------------------------ function () public payable { revert(); } // ------------------------------------------------------------------------ // Owner can transfer out any accidentally sent ERC20 tokens //所有者能够转移任何ERC20代币的接口 // ------------------------------------------------------------------------ function transferAnyERC20Token(address tokenAddress, uint tokens) public onlyOwner returns (bool success) { return ERC20Interface(tokenAddress).transfer(owner, tokens); }} |
本文链接： https://dreamerjonson.com/2018/11/26/solidity-55-token/
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