什麼是以太坊的ERC20標準代幣

歸根結底就是大夥兒一塊兒約定一段代碼的變量和函數命名和所表明的東西

在這套標準中核心的是如下幾個部分

1. totalSupply [表明的是token的總量]
2. balanceOf [這個爲一個數組,數組的key爲地址,value爲這個地址持有的token數量]
3. transfer(address _to, uint256 _value) returns (bool success) [判斷髮送數量是否正確]
4. transferFrom(address _from, address _to, uint256 _value) returns (bool success)[發起交易]

事件:

1. Transfer(address indexed _from, address indexed _to, uint256 _value). [當發起交易的時候調用]

 

如下爲XXXChain,簡稱XC,總量爲1億的代碼

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;
    }
}