Recently, i read smart contracts of compound finance.
In PriceOracleProxy.sol(https://etherscan.io/address/0xe7664229833AE4Abf4E269b8F23a86B657E2338D#code)
line 3863 shows:
address constant usdcOracleKey = address(1);
i'm confusing of this address(1), what's meaning of it.
/**
* #notice address of the cUSDC contract, which we hand pick a key for
*/
address public cUsdcAddress;
/**
* #notice address of the USDC contract, which we hand pick a key for
*/
address constant usdcOracleKey = address(1);
last used:
return v1PriceOracle.assetPrices(usdcOracleKey);
Its just another way to write 0x0000000000000000000000000000000000000001,
by the same logic address(0) is 0x0000000000000000000000000000000000000000
Related
I'm learning how the Uniswapv2 contracts work but I can't seem to wrap my mind around the swap() function.
Reference: https://github.com/Uniswap/v2-core/blob/master/contracts/UniswapV2Pair.sol#L173
Lines 173-174 contain:
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
My question is, when & whose balances are these?
A. These are the same as _reserve0 & _reserve1 after the most recent swap and will be used to synchronize reserves.
B. These are the quantities of each token the user making the swap currently possesses.
C. None of the above. It's something else. Please explain the flow of this function. I cannot find a clear and concise definition anywhere.
answer is "C" :)
balanceOf is a mapping in ERC20 implementation to return the amount that given address holds:
// address => holds uint amount
mapping(address => uint) public balanceOf;
Since current contract is inheriting from UniswapV2ERC20:
contract UniswapV2Pair is IUniswapV2Pair, UniswapV2ERC20{}
it can access to UniswapV2ERC20.sol
Since the mapping balanceOf is public, solidity assigns getters to the public variables
In the functions:
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
address(this) refers to the current contract which is UniswapV2Pair. So balance0 is how much the current contract owns _token0 and balance1 is how much the current contract address owns _token1. token0 and token1 are contract addresses and each ERC20 token contract, keeps track of addresses and their balances. so you are visiting each token contract and getting how much balance the current contract has.
Think ERC20 contract like a bank. you have token0 bank and token1 bank. Each bank keeps track of the balances of their users. balancesOf is where ERC20 tokens store those balances. Your current contract also owns some of those tokens so you just want to get how much tokens the current contract holds
swap function will be called by the user. Before executing the swap, contract checks if it has enough funds
uint amount0In = balance0 > _reserve0 - amount0Out ? balance0 - (_reserve0 - amount0Out) : 0;
uint amount1In = balance1 > _reserve1 - amount1Out ? balance1 - (_reserve1 - amount1Out) : 0;
require(amount0In > 0 || amount1In > 0, 'UniswapV2: INSUFFICIENT_INPUT_AMOUNT');
the Error being specified is
revert
The transaction has been reverted to the initial state.
Note: The called function should be payable if you send value and the value you send should be less than your current balance.
Debug the transaction to get more information.
//SPDX-License-Identifier:MIT
pragma solidity 0.8.8;
contract Giftcard{
event UniqueCardId(uint indexed Id,address indexed owner);
//Enter The Giftcard amount
//Pay the gift card by making multiple transations
//require(giftcard owner should approve the withdrawl )
address[] Giftcardowners;
mapping(address => uint) amountUploaded;
function Addamount() external payable{
require(msg.value >= 1 ether,"Gift card amount to small");
amountUploaded[msg.sender] = msg.value;
Giftcardowners.push(msg.sender);
emit UniqueCardId(Giftcardowners.length-1,msg.sender);
}
function GetGiftcard(uint _cardId) payable external {
require(Giftcardowners.length > _cardId,"Id doesnot exits");
address owner = Giftcardowners[_cardId-1];
uint amount = amountUploaded[owner];
require(amount >= 1 ether,"transfered is less than 1 ether");
// (bool successs,) = payable(msg.sender).call{value:amount}("");
//require(successs,"transaction reverted");
payable(msg.sender).transfer(1 ether);
}
function getBalance() external view returns(uint balance){
return address(this).balance;
}
}
Firstly I called the Addamount function by paying more than 1 ether to the smart contract
now after that when the GetGiftcard function is called the transaction is reverted. I am unable to find a solution
unable to understand the concept
Error is here
address owner = Giftcardowners[_cardId-1];
should be
address owner = Giftcardowners[_cardId];
When you call addAmount, this line executes
Giftcardowners.push(msg.sender);
in the Giftcardowners array you have only 1 item
Giftcardowners=[0x7EF2e0048f5bAeDe046f6BF797943daF4ED8CB47]
when you call the GetGiftcard, you need to pass _cardId=0, you are actually assigning the index of the array as the id. when you pass 0, index will be -1 here
address owner = Giftcardowners[_cardId-1];
You cannot pass 1 to get 1-1=0, because you have this condition
require(Giftcardowners.length > _cardId,"Id doesnot exits");
I am writing a solidity smart contract in which users would be able add a string (eg. one line joke), and other users should be able to vote on these jokes. If there are for example a million jokes in the contract (all with a different vote count), Would it be possible to rank these jokes by vote count? Eg. display the highest voted 10 of the million jokes? I know it is possible on a small scale, but on a larger scale I'm not so sure.
A variant of the contract that implements the main functionality you need is attached below:
registration of "jokes" records
registration of voting without repeats
definition of the top 10 (I hope I was not mistaken in the sorting algorithm).
The hash from its text is used as the identifier of the "joke".
However, in order to provide users with quality functionality, you need an external application that will monitor the events JokeCreated and JokeVoted of this contract and maintain an external database of "jokes" records.
This is because Ethereum contracts are ineffective for iterative operations with large arrays and you need an external service to:
providing users with a common list of "jokes"
providing users with a general rating list of "jokes"
When using an external application, you can also exclude the function of determining the top 10 from the contract (in function VotesForJoke), which will significantly reduce the cost of the voting transaction.
In addition, you need to keep in mind the problem of identifying users to avoid re-voting, since in general it cannot be solved at the level of Ethereum itself.
pragma solidity ^0.5.8;
contract Jokes
{
struct Joke
{
string text ;
address sender ;
bytes32 author ;
uint256 votes ;
mapping (bytes32=>bool) voters ;
}
mapping (bytes32 => Joke) JokesList ;
bytes32[10] Top10 ;
event JokeCreated(bytes32 hash, string text, address sender, bytes32 author) ;
event JokeVoted (bytes32 hash, bytes32 voter) ;
constructor() public
{
}
function NewJoke(string memory text_, bytes32 author_) public
{
bytes32 hash ;
hash=keccak256(abi.encodePacked(text_)) ;
if(JokesList[hash].author!=0x00) require(false) ;
JokesList[hash] =Joke({ text: text_,
sender: tx.origin,
author: author_,
votes: 0 }) ;
emit JokeCreated(hash, text_, tx.origin, author_) ;
}
function VotesForJoke(bytes32 hash_, bytes32 voter_) public
{
uint256 votes ;
uint256 i ;
// Check for existance
if(JokesList[hash_].author==0x00) require(false) ;
// Check for re-voting
if(JokesList[hash_].voters[voter_]==true) require(false) ;
JokesList[hash_].voters[voter_]=true ;
JokesList[hash_].votes++ ;
// Ordering top 10
votes=JokesList[hash_].votes ;
for(i=9 ; i>=0 ; i--)
if(votes>=JokesList[Top10[i]].votes)
{
if(i!=9 && Top10[i]!=hash_) Top10[i+1]=Top10[i] ;
}
else
{
break ;
}
if(i!=9) Top10[i+1]=hash_ ;
// Emit event of voting
emit JokeVoted(hash_, voter_) ;
}
function GetJoke(bytes32 hash_) public view returns (string memory, address, bytes32,uint256 retVal)
{
return(JokesList[hash_].text, JokesList[hash_].sender, JokesList[hash_].author, JokesList[hash_].votes) ;
}
function GetTop10() public view returns (bytes32[10] memory retVal)
{
return(Top10) ;
}
}
Aloha.
Web3 version is 0.20, and, according to documentation:
web3.eth.sendTransaction
web3.eth.sendTransaction(transactionObject [, callback])
Sends a transaction to the network.
Parameters
Object - The transaction object to send:
from: String - The address for the sending account. Uses the web3.eth.defaultAccount property, if not specified.
to: String - (optional) The destination address of the message, left undefined for a contract-creation transaction.
value: Number|String|BigNumber - (optional) The value transferred for the transaction in Wei, also the endowment if it's a contract-creation transaction.
gas: Number|String|BigNumber - (optional, default: To-Be-Determined) The amount of gas to use for the transaction (unused gas is refunded).
gasPrice: Number|String|BigNumber - (optional, default: To-Be-Determined) The price of gas for this transaction in wei, defaults to the mean network gas price.
data: String - (optional) Either a byte string containing the associated data of the message, or in the case of a contract-creation transaction, the initialisation code.
nonce: Number - (optional) Integer of a nonce. This allows to overwrite your own pending transactions that use the same nonce.
Number|String - (optional) If you pass this parameter it will not use the default block set with web3.eth.defaultBlock.
Function - (optional) If you pass a callback the HTTP request is made asynchronous. See this note for details.
I have function placeBet() which accepts multiple parameters:
function placeBet(uint8 _outcome, uint desiredMatchIndex, uint _amount) public payable{
// find a way to store a bid in order to be easily searchable, in order to easily send money to winners;
// require(!roundEnd, "Interactions with contract are locked, be careful next time!");
// require(state == State.Active, "Betting is over, game have already started!");
require(msg.value > 0, "It isn't possible to place a bet without a money ");
if(!isDuplicate(msg.sender)) addressIndices.push(msg.sender);
testina(msg.sender, _outcome, desiredMatchIndex);
existingBets[msg.sender].push(Bet({
bettor: msg.sender,
// name: name,
amount: _amount,
bet: desiredMatchIndex,
outcome: _outcome
}));
//emit event, finally;
}
, so my question is how should I include needed additional parameters (outcome, desiredMatchIndex, amount ) [maybe last one is reduntant ] alongside
transactionObject using web3.js?
Thanks : )
Oh, i am sorry, there was an example in documentation, just not adequately referenced.
/ Explicitly sending a transaction to this method
myContractInstance.myMethod.sendTransaction(param1 [, param2, ...] [, transactionObject] [, callback])
I am trying to create a smart contract using Solidity 0.4.4.
I was wondering if there is a way to set a mapping with some values already entered to an empty one?
For example:
This initailises a new mappping
mapping (uint => uint) map;
Here I add some values
map[0] = 1;
map[1] = 2;
How can I set the map back to empty without iterating through all the keys?
I have tried delete but my contract does not compile
Unfortunately, you can't. See the Solidity documentation for details on the reasons why. Your only option is to iterate through the keys.
If you don't know your set of keys ahead of time, you'll have to keep the keys in a separate array inside your contract.
I believe there is another way to handle this problem.
If you define your mapping with a second key, you can increment that key to essentially reset your mapping.
For example, if you wanted to your mapping to reset every year, you could define it like this:
uint256 private _year = 2021;
mapping(uint256 => mapping(address => uint256)) private _yearlyBalances;
Adding and retrieving values works just like normal, with an extra key:
_yearlyBalances[_year][0x9101910191019101919] = 1;
_yearlyBalances[_year][0x8101810181018101818] = 2;
When it's time to reset everything, you just call
_year += 1