以太坊智能合約Hello World示例程序

簡介

以太坊(Ethereum)是一提供個智能合約(smart contract)功能的公共區塊鏈(BlockChain)平臺. 本文介紹了一個簡單的以太坊智能合約的開發過程.

開發環境

在以太坊上開發應用，首先須要安裝其客戶端，本文使用基於Go語言的Geth, 其官網爲https://github.com/ethereum/go-ethereum.

第一步

在命令行環境中輸入如下命令, 鏈接到以太坊測試網絡

geth --testnet --fast --cache=512 console

第二步

在Geth提示符下輸入如下代碼, 建立一個用戶並設置密碼

personal.newAccount()

第三步

在Geth提示符下輸入如下代碼, 確認新用戶的帳戶餘額爲0, 並開始"挖礦"(mine)

eth.getBalance(eth.accounts[0])
miner.start()

第四步

新開一個命令行窗口並輸入如下命令, 將這個窗口鏈接到正在挖礦的窗口

geth attach

第五步

在Geth提示符下輸入如下代碼, 確認新用戶的帳戶餘額有所增加

eth.getBalance(eth.accounts[0])

第六步

使用智能合約的在線編譯器https://ethereum.github.io/browser-solidity/編譯如下代碼

contract HelloWorld
{
    address creator;
    string greeting;

    function HelloWorld(string _greeting) public
    {
        creator = msg.sender;
        greeting = _greeting;
    }

    function greet() constant returns (string)
    {
        return greeting;
    }

    function setGreeting(string _newgreeting)
    {
        greeting = _newgreeting;
    }

     /**********
     Standard kill() function to recover funds
     **********/

    function kill()
    {
        if (msg.sender == creator)
            suicide(creator);  // kills this contract and sends remaining funds back to creator
    }
}

第七步

編譯器生成的代碼以下

var _greeting = /* var of type string here */ ;
var helloworldContract = web3.eth.contract([{"constant":false,"inputs":[],"name":"kill","outputs":[],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_newgreeting","type":"string"}],"name":"setGreeting","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"greet","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"},{"inputs":[{"name":"_greeting","type":"string"}],"type":"constructor"}]);
var helloworld = helloworldContract.new(
   _greeting,
   {
     from: web3.eth.accounts[0],
     data: '606060405260405161044e38038061044e833981016040528080518201919060200150505b33600060006101000a81548173ffffffffffffffffffffffffffffffffffffffff021916908302179055508060016000509080519060200190828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f1061009e57805160ff19168380011785556100cf565b828001600101855582156100cf579182015b828111156100ce5782518260005055916020019190600101906100b0565b5b5090506100fa91906100dc565b808211156100f657600081815060009055506001016100dc565b5090565b50505b506103428061010c6000396000f360606040526000357c01000000000000000000000000000000000000000000000000000000009004806341c0e1b514610052578063a413686214610066578063cfae3217146100c15761004d565b610002565b34610002576100646004805050610141565b005b34610002576100bf6004808035906020019082018035906020019191908080601f0160208091040260200160405190810160405280939291908181526020018383808284378201915050505050509090919050506101d5565b005b34610002576100d36004805050610286565b60405180806020018281038252838181518152602001915080519060200190808383829060006004602084601f0104600302600f01f150905090810190601f1680156101335780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b600060009054906101000a900473ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff163373ffffffffffffffffffffffffffffffffffffffff1614156101d257600060009054906101000a900473ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16ff5b5b565b8060016000509080519060200190828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f1061022457805160ff1916838001178555610255565b82800160010185558215610255579182015b82811115610254578251826000505591602001919060010190610236565b5b5090506102809190610262565b8082111561027c5760008181506000905550600101610262565b5090565b50505b50565b602060405190810160405280600081526020015060016000508054600181600116156101000203166002900480601f0160208091040260200160405190810160405280929190818152602001828054600181600116156101000203166002900480156103335780601f1061030857610100808354040283529160200191610333565b820191906000526020600020905b81548152906001019060200180831161031657829003601f168201915b5050505050905061033f565b9056',
     gas: 4700000
   }, function (e, contract){
    console.log(e, contract);
    if (typeof contract.address !== 'undefined') {
         console.log('Contract mined! address: ' + contract.address + ' transactionHash: ' + contract.transactionHash);
    }
 })

第八步

修改編譯器生成的代碼, 設置顯示的字符串以及減小費用(gas)

var _greeting = "Hello World" ;

gas: 300000

第九步

將修改完的代碼複製到第四步的窗口中, 若是出現Error: account is locked undefined錯誤的話, 則使用personal.unlockAccount(eth.accounts[0], 'password')命令將用戶解鎖.

第十步

等候一段時間以後, geth窗口就會出現Contract mined! address..., 代表合約代碼發佈成功

第十一步

使用helloworld.greet()命令來運行該合約

總結

本文介紹了一個簡單的以太坊智能合約的開發過程.