以太坊ERC20合约Token生成

怎么生成以太坊ERC20合约Token？

所需工具

1. Chrome扩展metamask
2. 以太坊合约在线编译工具 remix

示例合约

注意保存好自己的合约源代码，留待验证时使用！！！

pragma solidity ^0.5.17;

contract Token {

    uint256 public totalSupply;

    function balanceOf(address _owner) public view returns (uint256 balance);

    function transfer(address _to, uint256 _value) public returns (bool success);

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);

    function approve(address _spender, uint256 _value) public returns (bool success);

    function allowance(address _owner, address _spender) public view returns (uint256 remaining);

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

contract StandardToken is Token {

    function transfer(address _to, uint256 _value) public returns (bool success) {
        //Default assumes totalSupply can't be over max (2^256 - 1).
        //If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
        //Replace the if with this one instead.
        //if (balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
        if (balances[msg.sender] >= _value && _value > 0) {
            balances[msg.sender] -= _value;
            balances[_to] += _value;
            emit Transfer(msg.sender, _to, _value);
            return true;
        } else { return false; }
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        //same as above. Replace this line with the following if you want to protect against wrapping uints.
        //if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
        if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
            balances[_to] += _value;
            balances[_from] -= _value;
            allowed[_from][msg.sender] -= _value;
            emit Transfer(_from, _to, _value);
            return true;
        } else { return false; }
    }

    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);
        return true;
    }

    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
      return allowed[_owner][_spender];
    }

    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;
}

contract Test is StandardToken {
    string public name;                   //fancy name
    uint8 public decimals;                //How many decimals to show. ie. There could 1000 base units with 3 decimals.
    string public symbol;                 //An identifier
    string public version = "1.0";       // 0.1 standard. Just an arbitrary versioning scheme.
    function TokenInit() public{
        balances[msg.sender] = 1000000000000;               // Give the creator all initial tokens
        totalSupply = 1000000000000;                        // Update total supply
        name = "Test";                                   // Set the name for display purposes
        decimals = 4;                            // Amount of decimals for display purposes
        symbol = "Test";                               // Set the symbol for display purposes
    }
}

修改的内容是最后一个类， 合约名称、初始量、给合约生成者的量等，注意初始量和给合约生成者的量是实际总量乘以10的精度次方。

步骤

1. 安装Chrome的metamask扩展
2. 生成账号并充值ETH，整个流程下来大约需要0.02~0.04个ETH
3. 打开remix，新建Solidity文件，复制以上合约到编辑框中并做相应的修改
4. 选择合适的编译器版本，这里用的是0.5.17，点击compile
5. 编译完成后切换到Run选项卡，点击Deploy，并在metamask弹出的窗口中确认
6. 合约生成完成后，调用TokenInit初始化
7. 调用transfer方法，将初始化好的Token转移给自己或另一个地址。
8. 结束。

Update 2020.6.8

旧版代码在使用0.5+的编译器编译时，会报如下错误

The state mutability modifier "constant" was removed in version 0.5.0. Use "view" or "pure" instead

相比旧版只兼容到0.4.12的合约代码，新代码兼容0.5.17，主要是修改了constant修饰符为view，以及添加public emit。

0.5以上的Solidity什么时候用view或pure？

如果是往存储里写东西，则什么标签也不用加；如果只读不写，用view；如果和读写存储没关系，比如1+1，则用pure。