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如果你想在以太坊ETH上发行一个ERC20的代币,你需要了解ERC20代币合约,通读本文以后,你将获得一个比较厉害的技能,希望你能学会。下图是基于ETH发行的ERC20版的USDT,你可以大概了解一下一个基本的ERC20代币的一些信息: https://cn.etherscan.com/token/0xdac17f958d2ee523a2206206994597c13d831ec7
什么是ERC20
可以把ERC20简单理解成以太坊上的一个代币协议,所有基于以太坊开发的代币合约都遵守这个协议。遵守这些协议的代币我们可以认为是标准化的代币,而标准化带来的好处是兼容性好。这些标准化的代币可以被各种以太坊钱包支持,用于不同的平台和项目。说白了,你要是想在以太坊上发行代币融资,必须要遵守ERC20标准。
ERC20的标准接口是这样的:
contract ERC20 {
function name() constant returns (string name)
function symbol() constant returns (string symbol)
function decimals() constant returns (uint8 decimals)
function totalSupply() constant returns (uint totalSupply);
function balanceOf(address _owner) constant returns (uint balance);
function transfer(address _to, uint _value) returns (bool success);
function transferFrom(address _from, address _to, uint _value) returns (bool success);
function approve(address _spender, uint _value) returns (bool success);
function allowance(address _owner, address _spender) constant returns (uint remaining);
event Transfer(address indexed _from, address indexed _to, uint _value);
event Approval(address indexed _owner, address indexed _spender, uint _value);
}
下面对上面的内容做一个简单的解释:
name
返回ERC20代币的名字,例如”My test token”。
symbol
返回代币的简称,例如:MTT,这个也是我们一般在代币交易所看到的名字。
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。
totalSupply
返回token的总供应量
balanceOf
返回某个地址(账户)的账户余额
transfer
从代币合约的调用者地址上转移_value的数量token到的地址_to,并且必须触发Transfer事件。
transferFrom
从地址_from发送数量为_value的token到地址_to,必须触发Transfer事件。transferFrom方法用于允许合同代理某人转移token。条件是from账户必须经过了approve。这个后面会举例说明。
approve
允许_spender多次取回您的帐户,最高达_value金额。 如果再次调用此函数,它将以_value覆盖当前的余量。
allowance
返回_spender仍然被允许从_owner提取的金额。
后面三个方法不好理解,这里还需要补充说明一下: approve是授权第三方(比如某个服务合约)从发送者账户转移代币,然后通过 transferFrom() 函数来执行具体的转移操作。
举例说明,如果账户A有1000个ETH,想允许B账户随意调用他的100个ETH,过程如下:
1. A账户按照以下形式调用approve函数approve(B,100)
2. B账户想用这100个ETH中的10个ETH给C账户,调用transferFrom(A, C, 10)
3. 调用allowance(A, B)可以查看B账户还能够调用A账户多少个token
发行ERC20代币步骤
MetaMask是钱包的一种,在chrome浏览器中,安装MetaMask插件即可,安装完成后,右上角会出现一个“狐狸头”的标志,点击该标志,打开钱包,第一步,创建账户,(创建账户只需要输入面密码即可,名称创建后可以随便改,该账户就是一个hash值,如何给自己创建的账户冲以太币呢,你可以通过在交易所买入一些ETH,然后转入即可)创建成功后,记住密码还有产生的几个随机单词(一定要记录下来)。
pragma solidity ^0.4.12;
contract IMigrationContract {
function migrate(address addr, uint256 nas) returns (bool success);
}
contract SafeMath {
function safeAdd(uint256 x, uint256 y) internal returns(uint256) {
uint256 z = x + y;
assert((z >= x) && (z >= y));
return z;
}
function safeSubtract(uint256 x, uint256 y) internal returns(uint256) {
assert(x >= y);
uint256 z = x - y;
return z;
}
function safeMult(uint256 x, uint256 y) internal returns(uint256) {
uint256 z = x * y;
assert((x == 0)||(z/x == y));
return z;
}
}
contract Token {
uint256 public totalSupply;
function balanceOf(address _owner) constant returns (uint256 balance);
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) constant returns (uint256 remaining);
event Transfer(address indexed _from, address indexed _to, uint256 _value);
event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}
/* ERC 20 token */
contract StandardToken is Token {
function transfer(address _to, uint256 _value) returns (bool success) {
if (balances[msg.sender] >= _value && _value > 0) {
balances[msg.sender] -= _value;
balances[_to] += _value;
Transfer(msg.sender, _to, _value);
return true;
} else {
return false;
}
}
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
balances[_to] += _value;
balances[_from] -= _value;
allowed[_from][msg.sender] -= _value;
Transfer(_from, _to, _value);
return true;
} else {
return false;
}
}
function balanceOf(address _owner) constant returns (uint256 balance) {
return balances[_owner];
}
function approve(address _spender, uint256 _value) returns (bool success) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}
function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
return allowed[_owner][_spender];
}
mapping (address => uint256) balances;
mapping (address => mapping (address => uint256)) allowed;
}
contract BliBliToken is StandardToken, SafeMath {
// metadata
string public constant name = "BliBli";
string public constant symbol = "BCoin";
uint256 public constant decimals = 18;
string public version = "1.0";
// contracts
address public ethFundDeposit; // ETH存放地址
address public newContractAddr; // token更新地址
// crowdsale parameters
bool public isFunding; // 状态切换到true
uint256 public fundingStartBlock;
uint256 public fundingStopBlock;
uint256 public currentSupply; // 正在售卖中的tokens数量
uint256 public tokenRaised = 0; // 总的售卖数量token
uint256 public tokenMigrated = 0; // 总的已经交易的 token
uint256 public tokenExchangeRate = 625; // 625 BILIBILI 兑换 1 ETH
// events
event AllocateToken(address indexed _to, uint256 _value); // 分配的私有交易token;
event IssueToken(address indexed _to, uint256 _value); // 公开发行售卖的token;
event IncreaseSupply(uint256 _value);
event DecreaseSupply(uint256 _value);
event Migrate(address indexed _to, uint256 _value);
// 转换
function formatDecimals(uint256 _value) internal returns (uint256 ) {
return _value * 10 ** decimals;
}
// constructor
function BliBliToken(
address _ethFundDeposit,
uint256 _currentSupply)
{
ethFundDeposit = _ethFundDeposit;
isFunding = false; //通过控制预CrowdS ale状态
fundingStartBlock = 0;
fundingStopBlock = 0;
currentSupply = formatDecimals(_currentSupply);
totalSupply = formatDecimals(10000000);
balances[msg.sender] = totalSupply;
if(currentSupply > totalSupply) throw;
}
modifier isOwner() { require(msg.sender == ethFundDeposit); _; }
/// 设置token汇率
function setTokenExchangeRate(uint256 _tokenExchangeRate) isOwner external {
if (_tokenExchangeRate == 0) throw;
if (_tokenExchangeRate == tokenExchangeRate) throw;
tokenExchangeRate = _tokenExchangeRate;
}
/// @dev 超发token处理
function increaseSupply (uint256 _value) isOwner external {
uint256 value = formatDecimals(_value);
if (value + currentSupply > totalSupply) throw;
currentSupply = safeAdd(currentSupply, value);
IncreaseSupply(value);
}
/// @dev 被盗token处理
function decreaseSupply (uint256 _value) isOwner external {
uint256 value = formatDecimals(_value);
if (value + tokenRaised > currentSupply) throw;
currentSupply = safeSubtract(currentSupply, value);
DecreaseSupply(value);
}
/// 启动区块检测 异常的处理
function startFunding (uint256 _fundingStartBlock, uint256 _fundingStopBlock) isOwner external {
if (isFunding) throw;
if (_fundingStartBlock >= _fundingStopBlock) throw;
if (block.number >= _fundingStartBlock) throw;
fundingStartBlock = _fundingStartBlock;
fundingStopBlock = _fundingStopBlock;
isFunding = true;
}
/// 关闭区块异常处理
function stopFunding() isOwner external {
if (!isFunding) throw;
isFunding = false;
}
/// 开发了一个新的合同来接收token(或者更新token)
function setMigrateContract(address _newContractAddr) isOwner external {
if (_newContractAddr == newContractAddr) throw;
newContractAddr = _newContractAddr;
}
/// 设置新的所有者地址
function changeOwner(address _newFundDeposit) isOwner() external {
if (_newFundDeposit == address(0x0)) throw;
ethFundDeposit = _newFundDeposit;
}
///转移token到新的合约
function migrate() external {
if(isFunding) throw;
if(newContractAddr == address(0x0)) throw;
uint256 tokens = balances[msg.sender];
if (tokens == 0) throw;
balances[msg.sender] = 0;
tokenMigrated = safeAdd(tokenMigrated, tokens);
IMigrationContract newContract = IMigrationContract(newContractAddr);
if (!newContract.migrate(msg.sender, tokens)) throw;
Migrate(msg.sender, tokens); // log it
}
/// 转账ETH 到BILIBILI团队
function transferETH() isOwner external {
if (this.balance == 0) throw;
if (!ethFundDeposit.send(this.balance)) throw;
}
/// 将BILIBILI token分配到预处理地址。
function allocateToken (address _addr, uint256 _eth) isOwner external {
if (_eth == 0) throw;
if (_addr == address(0x0)) throw;
uint256 tokens = safeMult(formatDecimals(_eth), tokenExchangeRate);
if (tokens + tokenRaised > currentSupply) throw;
tokenRaised = safeAdd(tokenRaised, tokens);
balances[_addr] += tokens;
AllocateToken(_addr, tokens); // 记录token日志
}
/// 购买token
function () payable {
if (!isFunding) throw;
if (msg.value == 0) throw;
if (block.number < fundingStartBlock) throw;
if (block.number > fundingStopBlock) throw;
uint256 tokens = safeMult(msg.value, tokenExchangeRate);
if (tokens + tokenRaised > currentSupply) throw;
tokenRaised = safeAdd(tokenRaised, tokens);
balances[msg.sender] += tokens;
IssueToken(msg.sender, tokens); //记录日志
}
}
到此为止,ERC20的合约已经部署完成!
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