什么是以太坊的ERC20标准代币

归根结底就是大伙儿一起约定一段代码的变量和函数命名和所代表的东西

在这套标准中核心的是以下几个部分

1. totalSupply [代表的是token的总量]
2. balanceOf [这个为一个数组,数组的key为地址,value为这个地址持有的token数量]
3. transfer(address _to, uint256 _value) returns (bool success) [判断发送数量是否正确]
4. transferFrom(address _from, address _to, uint256 _value) returns (bool success)[发起交易]

事件:

1. Transfer(address indexed _from, address indexed _to, uint256 _value). [当发起交易的时候调用]

以下为XXXChain,简称XC,总量为1亿的代码

pragma solidity ^0.4.8;
contract tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData); }

contract XXXChain {
    /* Public variables of the token */
    string public standard = 'XXXChain 0.1';
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;

    /* This creates an array with all balances */
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    /* This generates a public event on the blockchain that will notify clients */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /* This notifies clients about the amount burnt */
    event Burn(address indexed from, uint256 value);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    function GlobalBusinessChain() {
        balanceOf[msg.sender] =  100000000 * 1000000000000000000;              // Give the creator all initial tokens
        totalSupply =  100000000 * 1000000000000000000;                        // Update total supply
        name = "XXXChain";                                   // Set the name for display purposes
        symbol = "XC";                               // Set the symbol for display purposes
        decimals = 18;                            // Amount of decimals for display purposes
    }

    /* Send coins */
    function transfer(address _to, uint256 _value) {
        if (_to == 0x0) throw;                               // Prevent transfer to 0x0 address. Use burn() instead
        if (balanceOf[msg.sender] < _value) throw;           // Check if the sender has enough
        if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
        balanceOf[msg.sender] -= _value;                     // Subtract from the sender
        balanceOf[_to] += _value;                            // Add the same to the recipient
        Transfer(msg.sender, _to, _value);                   // Notify anyone listening that this transfer took place
    }

    /* Allow another contract to spend some tokens in your behalf */
    function approve(address _spender, uint256 _value)
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    /* Approve and then communicate the approved contract in a single tx */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    /* A contract attempts to get the coins */
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        if (_to == 0x0) throw;                                // Prevent transfer to 0x0 address. Use burn() instead
        if (balanceOf[_from] < _value) throw;                 // Check if the sender has enough
        if (balanceOf[_to] + _value < balanceOf[_to]) throw;  // Check for overflows
        if (_value > allowance[_from][msg.sender]) throw;     // Check allowance
        balanceOf[_from] -= _value;                           // Subtract from the sender
        balanceOf[_to] += _value;                             // Add the same to the recipient
        allowance[_from][msg.sender] -= _value;
        Transfer(_from, _to, _value);
        return true;
    }

    function burn(uint256 _value) returns (bool success) {
        if (balanceOf[msg.sender] < _value) throw;            // Check if the sender has enough
        balanceOf[msg.sender] -= _value;                      // Subtract from the sender
        totalSupply -= _value;                                // Updates totalSupply
        Burn(msg.sender, _value);
        return true;
    }

    function burnFrom(address _from, uint256 _value) returns (bool success) {
        if (balanceOf[_from] < _value) throw;                // Check if the sender has enough
        if (_value > allowance[_from][msg.sender]) throw;    // Check allowance
        balanceOf[_from] -= _value;                          // Subtract from the sender
        totalSupply -= _value;                               // Updates totalSupply
        Burn(_from, _value);
        return true;
    }
}