使用Mapping实现的以太坊智能合约的代码

• Step 1: 创建一个基础合约

pragma solidity ^0.4.7;

contract Coin {
    address public minter;
    mapping (address => uint) public balances;
}

这里我们定义了一个address 作为key, uint做为value的hashTable balances; 我们还定义了一个address的变量minter;

• Step 2: 添加一个构造函数Coin()

    function Coin() {
        minter = msg.sender;
    }

这里的代码minter = msg.sender; 代表创建这个合约的账户地址，被赋值给变量minter.

• Step 3: 添加一个挖矿合约

    function mint(address receiver, uint amount) {
        if (msg.sender != minter) throw;
        balances[receiver] += amount;
    }
  

这里的核心代码在于，如果调用这个方法的账户，不是minter, 也就是创建合约的账户的话，这个mint()将无法被执行。 只有是创建合约的账户，也就是minter 才可以执行它

• Step 4: 添加一个function send() 也就是从A转移X代币到B账户。代码如下：

    function send(address receiver, uint amount) {
        if (balances[msg.sender] < amount) return;
        balances[msg.sender] -= amount;
        balances[receiver] += amount;
    }
  

这个非常简单的转移货币的代码，也就是说msg.sender减少一定代币，接受者receiver增加一定代币

• Step 5: 定义一个事件 Sent()

    event Sent(address from, address to, uint amount);
  
    function send(address receiver, uint amount) {
        if (balances[msg.sender] < amount) return;
        balances[msg.sender] -= amount;
        balances[receiver] += amount;
        Sent(msg.sender, receiver, amount);
    }
  

完整代码如下：

pragma solidity ^0.4.7;

contract Coin {
    address public minter;
    mapping (address => uint) public balances;

    event Sent(address from, address to, uint amount);

    function Coin() {
        minter = msg.sender;
    }

    function mint(address receiver, uint amount) {
        if (msg.sender != minter) throw;
        balances[receiver] += amount;
    }

    function send(address receiver, uint amount) {
        if (balances[msg.sender] < amount) return;
        balances[msg.sender] -= amount;
        balances[receiver] += amount;
        Sent(msg.sender, receiver, amount);
    }
}