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This article mainly explains "Solidity programming development example analysis", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let Xiaobian take you to learn "Solidity programming development example analysis"!

Solidity Programming Examples

The smart contract tutorial that follows is very complex, but shows a lot of Solidity's programming features. It implements an introductory voting contract. The main problem with electronic voting, of course, is how to endow the right to vote with the right people and prevent manipulation. We can't solve all the problems, but at least we'll show how delegated votes can be counted automatically and transparently.

Voting Votes

The idea is to create a contract for each vote, giving each voting option a short name. The contract creator as president will give each voting participant their own address voting rights.

The people behind the address can choose to vote for themselves or entrust trusted representatives to vote for them. After voting, winningProposal() returns the proposal with the most votes.

/// @title Voting with delegation. /// @title Authorize voting contract Ballot { //complex type declared here //will be used in later arguments //represents an independent voter. struct Voter { uint weight; //cumulative weight. bool voted; //If true, the voter has voted. address delegate; //delegate's voting delegate uint vote; //Vote for proposal index number } //This is a type of independent proposal struct Proposal { bytes32 name; //Short name (32 bytes) uint voteCount; //Total votes received } public address chairperson; //Declare a state variable that holds the Voter structure for each individual address mapping(address => Voter) public voters; //A dynamic array that stores the `Proposal` structure Proposal[] public proposals; //Create a new vote for a proposal name `proposalNames`. function Ballot(bytes32[] proposalNames) { chairperson = msg.sender; voters[chairperson].weight = 1; //Create a new proposal for each proposal name provided //objects added to the end of the array for (uint i = 0; i

< proposalNames.length; i++) //`Proposal({...})` 创建了一个临时的提案对象， //`proposal.push(...)`添加到了提案数组`proposals`末尾。 proposals.push(Proposal({ name: proposalNames[i], voteCount: 0 })); } //给投票人`voter`参加投票的投票权， //只能由投票主持人`chairperson`调用。 function giveRightToVote(address voter) { if (msg.sender != chairperson || voters[voter].voted) //`throw`会终止和撤销所有的状态和以太改变。 //如果函数调用无效，这通常是一个好的选择。 //但是需要注意，这会消耗提供的所有gas。 throw; voters[voter].weight = 1; } // 委托你的投票权到一个投票代表 `to`。 function delegate(address to) { // 指定引用 Voter sender = voters[msg.sender]; if (sender.voted) throw; //当投票代表`to`也委托给别人时，寻找到最终的投票代表 while (voters[to].delegate != address(0) && voters[to].delegate != msg.sender) to = voters[to].delegate; // 当最终投票代表等于调用者，是不被允许的。 if (to == msg.sender) throw; //因为`sender`是一个引用， //这里实际修改了`voters[msg.sender].voted` sender.voted = true; sender.delegate = to; Voter delegate = voters[to]; if (delegate.voted) //如果委托的投票代表已经投票了，直接修改票数 proposals[delegate.vote].voteCount += sender.weight; else //如果投票代表还没有投票，则修改其投票权重。 delegate.weight += sender.weight; } ///投出你的选票（包括委托给你的选票） ///给 `proposals[proposal].name`。 function vote(uint proposal) { Voter sender = voters[msg.sender]; if (sender.voted) throw; sender.voted = true; sender.vote = proposal; //如果`proposal`索引超出了给定的提案数组范围 //将会自动抛出异常，并撤销所有的改变。 proposals[proposal].voteCount += sender.weight; } ///@dev 根据当前所有的投票计算出当前的胜出提案 function winningProposal() constant 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; } } Possible improvements

Now, assigning voting rights to all voting participants requires many transactions. Can you think of a better way?

blind beat

In this section, we will show how easy it is to create a complete blind-beat contract on ether. We start with a public auction where everyone can see the bids, and then expand the contract into a blind auction where the actual bids cannot be seen until the auction ends.

Simple public auction

Usually a simple open auction contract is one in which everyone can send their bid during the auction. In order to bind bidders to their auction, bidding involves sending an amount/ether. If a new highest bid is made, the previous highest bidder gets his money back. At the end of the auction phase, the beneficiary needs to manually invoke the contract to collect his money-the contract does not activate itself.

contract SimpleAuction { //auction parameters. //time is either unix absolute timestamp (seconds since 1970-01-01), //or is the block time in seconds address public beneficiary; uint public auctionStart; uint public biddingTime; //current auction status address public highestBidder; uint public highestBid; //set to true at the end to reject any changes bool ended; //Events that will be triggered when changed event HighestBidIncreased(address bidder, uint amount); event AuctionEnded(address winner, uint amount); //Here's a special comment called natspec, //Marked by 3 consecutive slashes, displayed when asking the user to confirm the transaction. ///Create a simple contract using `_biddingTime` to represent the auction time, ///Address `_beneficiary`. Represents the actual auctioneer function SimpleAuction(uint _biddingTime, address _beneficiary) { beneficiary = _beneficiary; auctionStart = now; biddingTime = _biddingTime; } ///Auction margin for the auction is sent with the transaction, ///will only be returned if the auction fails function bid() { //No parameters required, all information is already part of the transaction if (now > auctionStart + biddingTime) //Undo this call when the auction ends throw; if (msg.value = _time) throw; _ } modifier onlyAfter(uint _time) { if (now = value) if (placeBid(msg.sender, value)) refund -= value; //Guaranteed that the sender will never be able to retrieve the deposit twice bid.blindedBid = 0; } msg.sender.send(refund); } //This is an internal function, //means that only contracts (or contracts inherited from them) can be invoked function placeBid(address bidder, uint value) internal returns (bool success) { if (value

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