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June 13, 2018 06:28
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pragma solidity ^0.4.11; | |
contract SimpleAuction { | |
// Parameters of the auction. Times are either | |
// absolute unix timestamps (seconds since 1970-01-01) | |
// or time periods in seconds. | |
// final state of the auction | |
address public beneficiary; | |
uint public auctionEnd; | |
bool ended; | |
// current state of the auction | |
address public highestBidder; | |
uint public highestBid; | |
// Allowed withdrawls of previous bids | |
mapping(address => uint) pendingReturns; | |
event HighestBidIncreased(address bidder, uint amount); | |
event AuctionEnded(address winner, uint amount); | |
/// Three slash comments will be shown when a user is asked to confirm a transaction. | |
/// These are known as natspec comments | |
/// Create a simple auction with `_biddingTime` | |
/// seconds bidding time on behalf of the | |
/// beneficiary address `_beneficiary`. | |
function SimpleAuction(uint _biddingTime, address _beneficiary) public { | |
beneficiary = _beneficiary; | |
auctionEnd = now + _biddingTime; | |
} | |
/// Bid on the auction with the value sent | |
/// together with this transaction. | |
/// The value will only be refunded if the | |
/// auction is not won. | |
function bid() public payable { | |
require(now <= auctionEnd); | |
require(msg.value > highestBid); | |
if (highestBidder != 0) { | |
pendingReturns[highestBidder] += highestBid; | |
} | |
highestBidder = msg.sender; | |
highestBid = msg.value; | |
HighestBidIncreased(msg.sender, msg.value); | |
} | |
function withdraw() public returns (bool) { | |
uint amount = pendingReturns[msg.sender]; | |
if (amount > 0) { | |
// its important to set to 0 first because the recipient can call this function again as part of the receiving call | |
pendingReturns[msg.sender] = 0; | |
if (!msg.sender.send(amount)) { | |
// no need to call throw here,just reset the amount owing | |
pendingReturns[msg.sender] = amount; | |
return false; | |
} | |
} | |
return true; | |
} | |
/// End the auction and send the highest bid to the beneficiary | |
function auctionEnd() public { | |
// It is a good guideline to structure functions that interact | |
// with other contracts (i.e. they call functions or send Ether) | |
// into three phases: | |
// 1. checking conditions | |
// 2. performing actions (potentially changing conditions) | |
// 3. interacting with other contracts | |
// If these phases are mixed up, the other contract could call | |
// back into the current contract and modify the state or cause | |
// effects (ether payout) to be performed multiple times. | |
// If functions called internally include interaction with external | |
// contracts, they also have to be considered interaction with | |
// external contracts. | |
// 1. Conditions | |
require(now >= auctionEnd); | |
require(!ended); | |
// 2. Effects | |
ended = true; | |
AuctionEnded(highestBidder, highestBid); | |
// 3. Interactions | |
beneficiary.transfer(highestBid); | |
} | |
} |
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