區(qū)塊鏈是什么？一句話，它是一種特殊的分布式數(shù)據(jù)庫。首先，區(qū)塊鏈的主要作用是儲存信息。Any information that needs to be saved can be written to or read from the blockchain,so it is a database.

　　Secondly,anyone can set up a server,join the blockchain network,and become a node.區(qū)塊鏈的世界里面，沒有中心節(jié)點，每個節(jié)點都是平等的，都保存著整個數(shù)據(jù)庫。你可以向任何一個節(jié)點，寫入/讀取數(shù)據(jù)，因為所有節(jié)點最后都會同步，保證區(qū)塊鏈一致。

　　event DeployMarketEvent();

　　event ChangeMarketStatusEvent(uint8 status);

　　event SetTokenInfoEvent(uint16 tokenCode,string symbol,address tokenAddr,uint64 scaleFactor,uint minDeposit);

　　event SetWithdrawAddrEvent(address trader,address withdrawAddr);

　　event DepositEvent(address trader,uint16 tokenCode,string symbol,uint64 amountE8,uint64 depositIndex);

　　event WithdrawEvent(address trader,uint16 tokenCode,string symbol,uint64 amountE8,uint64 lastOpIndex);

　　event TransferFeeEvent(uint16 tokenCode,uint64 amountE8,address toAddr);

　　//`balanceE8`is the total balance after this deposit confirmation

　　event ConfirmDepositEvent(address trader,uint16 tokenCode,uint64 balanceE8);

　　//`amountE8`is the post-fee initiated withdraw amount

　　//`pendingWithdrawE8`is the total pending withdraw amount after this withdraw initiation

　　event InitiateWithdrawEvent(address trader,uint16 tokenCode,uint64 amountE8,uint64 pendingWithdrawE8);

　　event MatchOrdersEvent(address trader1,uint64 nonce1,address trader2,uint64 nonce2);

　　event HardCancelOrderEvent(address trader,uint64 nonce);

　　event SetFeeRatesEvent(uint16 makerFeeRateE4,uint16 takerFeeRateE4,uint16 withdrawFeeRateE4);

　　event SetFeeRebatePercentEvent(address trader,uint8 feeRebatePercent);

　　function Dex2(address admin_)public{

　　admin=admin_;

　　setTokenInfo(0/*tokenCode*/,"ETH",0/*tokenAddr*/,ETH_SCALE_FACTOR,0/*minDeposit*/);

　　emit DeployMarketEvent();

　　}

　　function()external{

　　revert();

　　}

　　//Change the market status of DEX.

　　function changeMarketStatus(uint8 status_)external{

　　if(msg.sender!=admin)revert();

　　if(marketStatus==CLOSED)revert();//closed is forever

　　marketStatus=status_;

　　emit ChangeMarketStatusEvent(status_);

　　}

　　//Each trader can specify a withdraw address(but cannot change it later).Once a trader's

　　//withdraw address is set,following withdrawals of this trader will go to the withdraw address

　　//instead of the trader's address.

　　function setWithdrawAddr(address withdrawAddr)external{

　　if(withdrawAddr==0)revert();

　　if(traders[msg.sender].withdrawAddr!=0)revert();//cannot change withdrawAddr once set

　　traders[msg.sender].withdrawAddr=withdrawAddr;

　　emit SetWithdrawAddrEvent(msg.sender,withdrawAddr);

　　}

　　//Deposit ETH from msg.sender for the given trader.

　　function depositEth(address traderAddr)external payable{

　　if(marketStatus!=ACTIVE)revert();

　　if(traderAddr==0)revert();

　　if(msg.value<tokens[0].minDeposit)revert();

　　if(msg.data.length!=4+32)revert();//length condition of param count

　　uint64 pendingAmountE8=uint64(msg.value/(ETH_SCALE_FACTOR/10**8));//msg.value is in Wei

　　if(pendingAmountE8==0)revert();

　　uint64 depositIndex=++lastDepositIndex;

　　setDeposits(depositIndex,traderAddr,0,pendingAmountE8);

　　emit DepositEvent(traderAddr,0,"ETH",pendingAmountE8,depositIndex);

　　}

　　//Deposit token(other than ETH)from msg.sender for a specified trader.