基于以太坊的投票系统（Solidity by Example —— Voting）

原文如下

pragma solidity ^0.4.16;

/// @title Voting with delegation.
contract Ballot {
// This declares a new complex type which will
// be used for variables later.
// It will represent a single voter.
struct Voter {
uint weight; // weight is accumulated by delegation
bool voted;  // if true, that person already voted
address delegate; // person delegated to
uint vote;   // index of the voted proposal
}

// This is a type for a single proposal.
struct Proposal {
bytes32 name;   // short name (up to 32 bytes)
uint voteCount; // number of accumulated votes
}

address public chairperson;

// This declares a state variable that
// stores a `Voter` struct for each possible address.
mapping(address => Voter) public voters;

// A dynamically-sized array of `Proposal` structs.
Proposal[] public proposals;

/// Create a new ballot to choose one of `proposalNames`.
function Ballot(bytes32[] proposalNames) public {
chairperson = msg.sender;
voters[chairperson].weight = 1;

// For each of the provided proposal names,
// create a new proposal object and add it
// to the end of the array.
for (uint i = 0; i < proposalNames.length; i++) {
// `Proposal({...})` creates a temporary
// Proposal object and `proposals.push(...)`
// appends it to the end of `proposals`.
proposals.push(Proposal({
name: proposalNames[i],
voteCount: 0
}));
}
}

// Give `voter` the right to vote on this ballot.
// May only be called by `chairperson`.
function giveRightToVote(address voter) public {
// If the argument of `require` evaluates to `false`,
// it terminates and reverts all changes to
// the state and to Ether balances. It is often
// a good idea to use this if functions are
// called incorrectly. But watch out, this
// will currently also consume all provided gas
// (this is planned to change in the future).
require(
(msg.sender == chairperson) &&
!voters[voter].voted &&
(voters[voter].weight == 0)
);
voters[voter].weight = 1;
}

/// Delegate your vote to the voter `to`.
function delegate(address to) public {
// assigns reference
Voter storage sender = voters[msg.sender];
require(!sender.voted);

// Self-delegation is not allowed.
require(to != msg.sender);

// Forward the delegation as long as
// `to` also delegated.
// In general, such loops are very dangerous,
// because if they run too long, they might
// need more gas than is available in a block.
// In this case, the delegation will not be executed,
// but in other situations, such loops might
// cause a contract to get "stuck" completely.
while (voters[to].delegate != address(0)) {
to = voters[to].delegate;

// We found a loop in the delegation, not allowed.
require(to != msg.sender);
}

// Since `sender` is a reference, this
// modifies `voters[msg.sender].voted`
sender.voted = true;
sender.delegate = to;
Voter storage delegate_ = voters[to];
if (delegate_.voted) {
// If the delegate already voted,
// directly add to the number of votes
proposals[delegate_.vote].voteCount += sender.weight;
} else {
// If the delegate did not vote yet,
// add to her weight.
delegate_.weight += sender.weight;
}
}

/// Give your vote (including votes delegated to you)
/// to proposal `proposals[proposal].name`.
function vote(uint proposal) public {
Voter storage sender = voters[msg.sender];
require(!sender.voted);
sender.voted = true;
sender.vote = proposal;

// If `proposal` is out of the range of the array,
// this will throw automatically
ed74
and revert all
// changes.
proposals[proposal].voteCount += sender.weight;
}

/// @dev Computes the winning proposal taking all
/// previous votes into account.
function winningProposal() public view
returns (uint winningProposal_)
{
uint winningVoteCount = 0;
for (uint p = 0; p < proposals.length; p++) {
if (proposals[p].voteCount > winningVoteCount) {
winningVoteCount = proposals[p].voteCount;
winningProposal_ = p;
}
}
}

// Calls winningProposal() function to get the index
// of the winner contained in the proposals array and then
// returns the name of the winner
function winnerName() public view
returns (bytes32 winnerName_)
{
winnerName_ = proposals[winningProposal()].name;
}
}

中文注释：pragma solidity ^0.4.16; //注释Solidity版本//合约名contract Ballot {// 投票者结构体struct Voter {uint weight; // 份额（既拥有多少票）bool voted; // 是否已经投票address delegate; // 委任谁进行投票uint vote; // 第几个投票议案}// 议案机构体struct Proposal {bytes32 name; // 议案名(最多32字节)uint voteCount; // 累计投票数}address public chairperson; //投票主持人// 投票者与其地址的映射mapping(address => Voter) public voters;// 提案指针Proposal[] public proposals;/// Ballot函数，创建新投票，输入多个议案名function Ballot(bytes32[] proposalNames) public {chairperson = msg.sender;voters[chairperson].weight = 1;for (uint i = 0; i < proposalNames.length; i++) {// `Proposal({...})` 创建一个临时Proposal对象proposals.push(Proposal({name: proposalNames[i],voteCount: 0}));}}//输入投票者地址，给予投票者投票权限function giveRightToVote(address voter) public {// require防止函数被错误调用，判断为错误时终止调用// 并恢复到调用前的状态，但是注意会消耗gasrequire((msg.sender == chairperson) &&!voters[voter].voted &&(voters[voter].weight == 0));voters[voter].weight = 1;}/// 输入他人地址，委任他人投票function delegate(address to) public {Voter storage sender = voters[msg.sender];require(!sender.voted);// 不允许委任自己require(to != msg.sender);// 循环委任直至被委任人不再委任他人，// 但注意这种循环是危险的，有可能耗尽gas来进行计算。while (voters[to].delegate != address(0)) {to = voters[to].delegate;// 避免循环委任，形成委任环链require(to != msg.sender);}// 此处sender为voters[msg.sender]sender.voted = true;sender.delegate = to;Voter storage delegate_ = voters[to];if (delegate_.voted) {// 如果被委任人已经投票，直接增加该议案票数proposals[delegate_.vote].voteCount += sender.weight;} else {// 如果被委任人未投票，增加被委任人持有票数delegate_.weight += sender.weight;}}/// 向议案投票function vote(uint proposal) public {Voter storage sender = voters[msg.sender];require(!sender.voted);sender.voted = true;sender.vote = proposal;// 提案超出数组范围时自动中断并恢复所以修改proposals[proposal].voteCount += sender.weight;}/// 返回获得票数最高的议案索引function winningProposal() public viewreturns (uint winningProposal_){uint winningVoteCount = 0;for (uint p = 0; p < proposals.length; p++) {if (proposals[p].voteCount > winningVoteCount) {winningVoteCount = proposals[p].voteCount;winningProposal_ = p;}}}// 返回获得票数最高的议案名function winnerName() public viewreturns (bytes32 winnerName_){winnerName_ = proposals[winningProposal()].name;}}