一 主要完成以下功能1.自己转账给他人(transfer)2.自己帮别人转账给另外一个人(transferFrom)3.我委托你帮我管理我的代币，使用权给你,但是币还在我这(approve)4.查看一下我还有多少币委托你在管理(allowance)二 规范地址: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md三 方法 function name() public view returns(string) 返回代币名称 function symbol() public view returns (string) 返回代币符号 function decimals() public view returns (uint8) 返回代币的精度(代币可以被分为几份,常用的为8) function totalSupply() public view returns (uint256) 返回总供应量 function balanceOf(address _owner) public view returns (uint256 balance) 返回某个账号里的代币余额 function transfer(address _to, uint256 _value) public returns (bool success) 自己转账给他人(transfer) function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) 自己帮别人转账给另外一个人(transferFrom) function approve(address _spender, uint256 _value) public returns (bool success) 我委托你帮我管理我的代币，使用权给你,但是币还在我这(approve) function allowance(address _owner, address _spender) public view returns (uint256 remaining) 查看一下我还有多少币委托你在管理(allowance)四 事件 event Transfer(address indexed _from, address indexed _to, uint256 _value) 转账时发生 event Approval(address indexed _owner, address indexed _spender, uint256 _value) 委托时发生五 例子一 /* Implements EIP20 token standard: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md .*/ pragma solidity ^0.4.21; import "./EIP20Interface.sol"; contract EIP20 is EIP20Interface { uint256 constant private MAX_UINT256 = 2**256 - 1; mapping (address => uint256) public balances; mapping (address => mapping (address => uint256)) public allowed; /* NOTE: The following variables are OPTIONAL vanities. One does not have to include them. They allow one to customise the token contract & in no way influences the core functionality. Some wallets/interfaces might not even bother to look at this information. */ string public name; //fancy name: eg Simon Bucks uint8 public decimals; //How many decimals to show. string public symbol; //An identifier: eg SBX function EIP20( uint256 _initialAmount, string _tokenName, uint8 _decimalUnits, string _tokenSymbol ) public { balances[msg.sender] = _initialAmount; // Give the creator all initial tokens totalSupply = _initialAmount; // Update total supply name = _tokenName; // Set the name for display purposes decimals = _decimalUnits; // Amount of decimals for display purposes symbol = _tokenSymbol; // Set the symbol for display purposes } function transfer(address _to, uint256 _value) public returns (bool success) { require(balances[msg.sender] >= _value); balances[msg.sender] -= _value; balances[_to] += _value; emit Transfer(msg.sender, _to, _value); //solhint-disable-line indent, no-unused-vars return true; } function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) { uint256 allowance = allowed[_from][msg.sender]; require(balances[_from] >= _value && allowance >= _value); balances[_to] += _value; balances[_from] -= _value; if (allowance < MAX_UINT256) { allowed[_from][msg.sender] -= _value; } emit Transfer(_from, _to, _value); //solhint-disable-line indent, no-unused-vars return true; } function balanceOf(address _owner) public view returns (uint256 balance) { return balances[_owner]; } function approve(address _spender, uint256 _value) public returns (bool success) { allowed[msg.sender][_spender] = _value; emit Approval(msg.sender, _spender, _value); //solhint-disable-line indent, no-unused-vars return true; } function allowance(address _owner, address _spender) public view returns (uint256 remaining) { return allowed[_owner][_spender]; } } 六 例子二 pragma solidity ^0.4.24; import "./IERC20.sol"; import "../../math/SafeMath.sol"; /** * @title Standard ERC20 token * * @dev Implementation of the basic standard token. * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md * Originally based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol */ contract ERC20 is IERC20 { using SafeMath for uint256; mapping (address => uint256) private _balances; mapping (address => mapping (address => uint256)) private _allowed; uint256 private _totalSupply; /** * @dev Total number of tokens in existence */ function totalSupply() public view returns (uint256) { return _totalSupply; } /** * @dev Gets the balance of the specified address. * @param owner The address to query the balance of. * @return An uint256 representing the amount owned by the passed address. */ function balanceOf(address owner) public view returns (uint256) { return _balances[owner]; } /** * @dev Function to check the amount of tokens that an owner allowed to a spender. * @param owner address The address which owns the funds. * @param spender address The address which will spend the funds. * @return A uint256 specifying the amount of tokens still available for the spender. */ function allowance( address owner, address spender ) public view returns (uint256) { return _allowed[owner][spender]; } /** * @dev Transfer token for a specified address * @param to The address to transfer to. * @param value The amount to be transferred. */ function transfer(address to, uint256 value) public returns (bool) { require(value <= _balances[msg.sender]); require(to != address(0)); _balances[msg.sender] = _balances[msg.sender].sub(value); _balances[to] = _balances[to].add(value); emit Transfer(msg.sender, to, value); return true; } /** * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. * Beware that changing an allowance with this method brings the risk that someone may use both the old * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 * @param spender The address which will spend the funds. * @param value The amount of tokens to be spent. */ function approve(address spender, uint256 value) public returns (bool) { require(spender != address(0)); _allowed[msg.sender][spender] = value; emit Approval(msg.sender, spender, value); return true; } /** * @dev Transfer tokens from one address to another * @param from address The address which you want to send tokens from * @param to address The address which you want to transfer to * @param value uint256 the amount of tokens to be transferred */ function transferFrom( address from, address to, uint256 value ) public returns (bool) { require(value <= _balances[from]); require(value <= _allowed[from][msg.sender]); require(to != address(0)); _balances[from] = _balances[from].sub(value); _balances[to] = _balances[to].add(value); _allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value); emit Transfer(from, to, value); return true; } /** * @dev Increase the amount of tokens that an owner allowed to a spender. * approve should be called when allowed_[_spender] == 0. To increment * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol * @param spender The address which will spend the funds. * @param addedValue The amount of tokens to increase the allowance by. */ function increaseAllowance( address spender, uint256 addedValue ) public returns (bool) { require(spender != address(0)); _allowed[msg.sender][spender] = ( _allowed[msg.sender][spender].add(addedValue)); emit Approval(msg.sender, spender, _allowed[msg.sender][spender]); return true; } /** * @dev Decrease the amount of tokens that an owner allowed to a spender. * approve should be called when allowed_[_spender] == 0. To decrement * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol * @param spender The address which will spend the funds. * @param subtractedValue The amount of tokens to decrease the allowance by. */ function decreaseAllowance( address spender, uint256 subtractedValue ) public returns (bool) { require(spender != address(0)); _allowed[msg.sender][spender] = ( _allowed[msg.sender][spender].sub(subtractedValue)); emit Approval(msg.sender, spender, _allowed[msg.sender][spender]); return true; } /** * @dev Internal function that mints an amount of the token and assigns it to * an account. This encapsulates the modification of balances such that the * proper events are emitted. * @param account The account that will receive the created tokens. * @param amount The amount that will be created. */ function _mint(address account, uint256 amount) internal { require(account != 0); _totalSupply = _totalSupply.add(amount); _balances[account] = _balances[account].add(amount); emit Transfer(address(0), account, amount); } /** * @dev Internal function that burns an amount of the token of a given * account. * @param account The account whose tokens will be burnt. * @param amount The amount that will be burnt. */ function _burn(address account, uint256 amount) internal { require(account != 0); require(amount <= _balances[account]); _totalSupply = _totalSupply.sub(amount); _balances[account] = _balances[account].sub(amount); emit Transfer(account, address(0), amount); } /** * @dev Internal function that burns an amount of the token of a given * account, deducting from the sender's allowance for said account. Uses the * internal burn function. * @param account The account whose tokens will be burnt. * @param amount The amount that will be burnt. */ function _burnFrom(address account, uint256 amount) internal { require(amount <= _allowed[account][msg.sender]); // Should https://github.com/OpenZeppelin/zeppelin-solidity/issues/707 be accepted, // this function needs to emit an event with the updated approval. _allowed[account][msg.sender] = _allowed[account][msg.sender].sub( amount); _burn(account, amount); } }