I'm trying to create a function that destroys tokens in an address.
The remix has the error
DeclarationError: Undeclared identifier
mostly for totalSupply.
Can anyone check what the error is in the syntax and how to solve it?
Is this the best function, or is it better to remove the tokens and send them to the dead address, or to the contract itself, or even to leave it in the wallet of the holder and block their movement in the wallet forever? I would like advice (and mainly how to solve this code).
/**
#dev removes tokens from an account and decreases the token supply
can only be called by the contract owner
_from account to remove the amount from
_amount amount to decrease the supply by
*/
function removeTokens(address _from, uint256 _amount) public onlyOwner
{
balanceOf[_from] = sub(balanceOf[_from], _amount);
totalSupply = sub(totalSupply, _amount);
Transfer(_from, this, _amount);
Destruction(_amount);
}
Sub is the subtraction function of values (SafeMath)
Related
I am experimenting with solidity and I faced an issue for what I could not find a solution.
The program should let addresses buy ticket at a preset price, and the owner can start the "roll the dice" function which randomly selects the winner and transfer the funds to that address.
I beleive that this program would be easier with mapping instead of array, but getting experience with array was the main purpose of this program.
The error happens when the user calls buyTicket function. Based on the response I beleive the contract comsumes too much gas. Can someone tell me why it doesnt work? I appreciate any other helping comment regarding the rest of the code:)
Thanks in advance!
// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;
contract Lottery {
constructor () {
owner = msg.sender;
}
address[] public Players;
address private owner;
uint public ticketPrice;
uint public price;
uint public nonce;
uint public variations;
address payable winner;
bool hasTicketAnswer;
event Winner(address _winner);
event PriceSet(uint _setPrice);
event TicketBought();
function setTicketPrice(uint _ticketPrice) public {
require(msg.sender == owner, "Only Owner...");
ticketPrice = _ticketPrice;
emit PriceSet(_ticketPrice);
}
function hasTicket(address _sender) private returns(bool) {
hasTicketAnswer = false;
for (uint i = 0; i < Players.length; i++) {
if (Players[i] == _sender) hasTicketAnswer = true;
}
return hasTicketAnswer;
}
function buyTicket() external payable {
require(ticketPrice > 0, "Price did not set, be patient...");
require(hasTicket(msg.sender) == false, "You cannot have two tickets...");
require(msg.sender.balance <= ticketPrice, "Insufficient funds...");
payable(address(this)).transfer(ticketPrice);
Players.push(address(msg.sender));
price += msg.value;
emit TicketBought();
}
function checkBalance() public view returns(uint) {
return address(this).balance;
}
function rollTheDice() public payable {
variations = Players.length;
winner = payable(Players[uint(keccak256(abi.encodePacked(msg.sender, nonce, block.timestamp))) % variations]);
winner.transfer(price);
emit Winner(winner);
}
receive () external payable {
}
}
Besides probably finding the problem, I've read some things that I'd like to comment on.
Your problem
The reason why you're getting the "Insufficient funds" error is because the condition is returning false. You're asking the msg.sender balance to be less than or equal (<=) to ticketPrice, when it should be more than or equal (>=).
Let's say Alice has a balance of 0.05 ETH and interacts with the contract whose ticket price is 0.001 ETH...
require(0.05 ETH <= 0.001 ETH) // Reverting...
Observations
I'm curious if you're intentionally coding the buyTicket function in that way. What it actually does is checking if the msg.sender has enough ETH to buy a ticket in its wallet, which doesn't mean that the user is effectively sending ETH in the transaction (the amount of wei sent in the transaction can be checked with msg.value, you can read more about it here).
My last observation is the payable(address(this)).transfer(ticketPrice) line of code, because it's not necessary to do so, once a payable function receives ETH, it is saved into the contract... In that line you're just making the Bob's contract to send ETH to the Bob's contract, which just wastes gas without reason
I hope I've helped with you and if I wasn't completely clear in any thing I've said don't doubt in asking me
I trying to understand how crowdsale work in this way of buying tokens.
The part of send ether to a contract is ok, but the part of token transfer is still dark for me.
I have a ERC20Mintable token, in the latest version of openzeppelin.
My crowdsale contract will have thousands and thousands of buyers. In most tutorials, they teach transfering tokens with transferFrom, but that requires the approval of ERC20 owner correct ? Is what most of tutorials show. I can mint either, probably because only owner can mint tokens.
My question is: there is a method that users can buy tokens without any action of the ERC20 owner?
Thanks!
Owner approval is needed for transferFrom function. Because with this function you are allowing third-party account transfer from your account to someone.
Let's say I want to transfer token from your account to my brother's account. To be able to do this, you have to give permission first and this permission is stored in a mapping. If you allow me to transfer a specific amount from your account, you first add my account into this mapping
// my address is allowed to transfer token to other address
mapping(address=>mapping(address=>uint256)) allowed;
with approve function.
function approve(address _spender, uint256 _value) public override returns (bool success){
// you are calling this. so you are the msg.sender
// first we are checking if you have enough token to be transferred
require(tokenBalances[msg.sender]>=_value,"insufficient token");
// then you register my account with the _value
allowed[msg.sender][_spender]=_value;
// if in the future there is a dispute, we can check those events for verification
emit Approval(msg.sender,_spender,_value);
return true;
}
This where owner approval used. If you want to transfer money from your account to another account, you use the transfer function:
function transfer(address _to, uint256 _value) public override returns (bool success){
require(tokenBalances[msg.sender]>=_value,"you do not have enough tokens");
tokenBalances[msg.sender]-=_value;
tokenBalances[_to]+=_value;
emit Transfer(msg.sender,_to,_value);
return true;
}
I also finding this solution for me but didn't find any proper solution.
however find a solution for now.
create a function that is payable and pass amount(how much buyer buy) and make a keccak hash with (sender , value and amount) and store in a map and send transfer receive eth to _admin address.
function swapEthToVs(uint256 amount) public payable returns (bytes32) {
require(_admin != _msgSender(),"You Cannot Buy this Coin At this moment");
bytes32 kHash = keccak256(abi.encodePacked(msg.value,amount,_msgSender()));
swapHash[_origin()] = kHash;
payable(address(_admin)).transfer(msg.value);
return kHash;
}
then create api that take (sender , amount ,contractOwner) and call another function with contractOwnerSigner
function verifySwapHash(uint256 eth,address to,uint256 amount) public returns (bool) {
require(swapHash[to] == keccak256(abi.encodePacked(eth, amount, to)),"Invalid hash no trace found");
transfer(to, amount);
delete swapHash[to];
return true;
}
I know this is risky but i didn't found any solution. if you found any solution please describe solution.
Here are the steps I follow on Remix:
Deploy my ERC20Basic token and my DEX contract.
DEX.buy > Buy ERC20Basic tokens in exchange of ETH (works fine).
ERC20Basic.approve(contractAddress, tokenAmount) (works fine).
ERC20Basic.allowance > Works fine, function returns the amount of the allowance.
The problem comes when I try to sell tokens with this function from my DEX contract:
function sell(uint256 amount) public {
uint256 allowance = token.allowance(msg.sender, address(this));
require(allowance >= amount, "Check the token allowance");
token.transferFrom(msg.sender, address(this), amount);
payable(msg.sender).transfer(amount);
emit Sold(amount);
}
I still get "Check the token allowance".
When I log the allowance I get 0.
When I log msg.sender and address(this), I get the same addresses I used on the Remix interface to get the value of the allowance manually.
It feels like the allowance is reset to 0 when I call the sell function or that the sell function can't reach the value of the allowance. Maybe this is something about memory and storage?
My allowance function inside of ERC20Basic contract is:
function allowance(address owner, address delegate)
public
view
override
returns (uint256)
{
return allowed[owner][delegate];
}
Approval function:
function approve(address delegate, uint256 numTokens)
public
override
returns (bool)
{
allowed[msg.sender][delegate] = numTokens;
emit Approval(msg.sender, delegate, numTokens);
return true;
}
Allowance structure:
mapping(address => mapping(address => uint256)) allowed;
How are you calling the approve function?
In your code you aren't passing the require statement because your approval wasn't successful. If it was your allowance wouldn't be 0.
You are probably calling the approve function from the contract which won't work because then the msg.sender would be address of the contract not your accounts address.
You have to approve the amount manually outside of the contract for it to work.
I'm really really inexperienced with contracts and need your help. I created a contract with remix and sent some bnb to it. I want to retrieve it but I can't seem to make it happen.
pragma solidity ^0.8;
interface IERC20 {
function transfer(address _to, uint256 _amount) external returns (bool);
}
contract MyContract {
function withdrawToken(address _tokenContract, uint256 _amount) external {
IERC20 tokenContract = IERC20(_tokenContract);
// transfer the token from address of this contract
// to address of the user (executing the withdrawToken() function)
tokenContract.transfer(msg.sender, _amount);
}
}
This is the code that I'm using from another post but I don't understand it. Do I have to change the "_to" "and "_amount" with the numbers or do I just copy the code and compile it?
I'm really sorry but I have no idea what I did so I just want to take the tokens back.
Thanks
Sorry but you can't withdraw your bnb, bnb isn't a token, bnb is like the ether in ethereum, the native chain currency and the contract doesn't have a function to let you withdraw it, the only way is if you send wbnb, in that case you can look the address of the contract of the wbnb and call the function withdraw of the contract you made
As Jhonny said, BNB is not an actual token, and so your implemented logic won't work to withdraw BNB. But just for you to know, you could create a function which only allows withdrawing BNB (which is the native currency). It would be something like this:
function withdraw(uint _amount) external {
payable(msg.sender).transfer(_amount);
}
Hope you find this useful.
What would cause my reclaim function that was working before to suddenly stop working as I add other functionality to the the contract?
DeclarationError: Undeclared identifier. Did you mean "_balance"?
uint256 _balance = balances[this];
^^^^^^^^^^
It is flagging on every "balances" in this fragment:
function reclaimPAXG() external onlyOwner {
uint256 _balance = balances[this];
balances[this] = 0;
balances[owner] = balances[owner].add(_balance);
emit Transfer(this, owner, _balance);
}
with balances mapped:
mapping(address => uint256) internal balances;
This is Solidity 0.8.4 and I am interfacing IERC20 into the token contract and I tried several potential fixes.
Attempted to move it into the Ownable contract and it kept the error. The closest other search result is a grammatical error so I don't know what's happening.
Was able to get past the balances error by moving the IERC20 interface into the token contract where its mapping is. Ended up deleting an extra "balanceOf" function which may have been causing the problem.