All Questions

There are a lot of tools to prepare JavaScript/CSS code for production, e.g. to minimize, to convert ES8 code to ES5. Is there a tool to automatically apply SafeMath library to a .sol file? The ...

New to blockchain.. havent a clue.. I managed to create a new contract with Eth. I moved money from MyEtherum Wallet to Metamask and into a contract, somehow? I have no coding experience but need ...

I wrote code to buy DAI using ETH on Uniswap V2 as follows: function buyCryptoOnUniswap(uint256 etherCost , address cryptoToken) public payable returns(uint256){ //address cryptoToken = ...

function isOwner(address _owner) public view returns (bool isOwner) { return owners[_owner]; } function isOwnerChoice(address _owner, address _newOwner) public view returns (bool ...

Hi guys I got this error when I try to compile using truffle develop. truffle(develop)> compile Compiling your contracts... Compiling ./contracts/StarNotary.sol /mnt/d/Blockchain/...

I want to install solc 0.4.24 but the commands given below installs the new version. sudo add-apt-repository ppa:ethereum/ethereum sudo apt-get update sudo apt-get install solc Or sudo snap install ...

Is Absolute/ Immediate Finality a goal in blockchain consensus or does some areas work better under probabilistic finality such as Ethereum's Pow and to be PoS? (I know that some networks using BFT ...

In Solidity, what's the difference between funtion type and funtion? And what can they be used for and how respectively? Thanks!

So, I recently created a standard ERC20 token but I need to implement "mint" and "owner" functionality. I see that in older implementations but openzeppelin no longer has contracts ...

I have below smart contract and a test program to test transfer ETH out of contract address, but contract’s ETH balance not changed. I tested withdrawAmount(uint256 amount) but the assertion error ...

I am learning blockchain, but it has been impossible to pass from this error: Fatal:account unlock with HTTP access is forbidden. I am using Ubuntu in a virtual machine. Please help me

I am currently developing a Dapp in vue.js/node.js which will use MetaMask to interact with the Ethereum Network. I have the following code implemented in a JavaScript module. import web3 from 'web3';...

I want to write a contract that uses USDT (Tether) for payment. How can I use the ERC20 token as an ERC777 token, for example: Use a fallback function that executes when we receive USDT token. Or use ...

So Im having some trouble with sending ETH from one account to another trough web3 with an erc20 smart contract and I`m using Infura RPC. So, my process is to send 0.2 ETH from account 1 to account 2 ...

First of all, excuse me if this is not the section to ask. I'm trying to find out what information can be encrypted inside the blockchain, i.e. should all the information written in the blocks be (...

https://feeds.chain.link/ - link for reference. Let's take the LINK/USD feed for example: From my understanding, the aggregation contract fetches the price of LINK in USD from the node operators who ...

I'm learning how to build a smart contract that is able to receive ETH and, if certain conditions are met, send ETH back to the address from which it received it. My understanding currently is that a ...

I'm trying to use a mapping inside a struct: struct PoolStruct { uint currentUserID; uint activeUserID; uint price; uint minimalReferrals; mapping(uint => address) poolUserList; ...

I am trying to create a simple function that buys a token from uniswap (v1) and then immediately sells the token back to ether. I am able to buy successfully but when adding the calls to the sell ...

Here's an example contract: Nobody.sol pragma solidity ^0.4.17; contract Nobody { function die() public { selfdestruct(msg.sender); } } The solc JSON specification to compile the ...

I had the experience of losing a Geth server due to some unknown software issues and whatever I could do for that time was moving keystore files to a new server. But it was a Geth server in fast mode. ...

let Event = artifacts.require("./Event.sol"); const field= { nameOfEvent : "Music", ticketCount : 100, ticketCharge :10000, durationInMinute :1200 } module....

Making a react native app and I'm using drizzle. I'd like to instantiate the Drizzle object with the logged in user's accounts. Currently it's taking the accounts from my ganache testchain described ...

I just got access to a old ether wallet with all my DAO tokens. Is it too late, no way to convert them back to Ether? any way at all?

I've heard a lot about Chainlink recently -- how Synthetix, Aave and other top Defipulse projects are using them. How exactly does Chainlink solve the oracle problem from a technical perspective?

Anybody used WalletConnect in react-native? How do you genreate a topic and key for the URI? From the docs: Android has the easiest integration as it's operating system is designed to handle multiple ...

I've been reading a lot about how smart contracts work, and I'm a little new to the area, but why do we need decentralized oracles? It feels like I can just make an API call from wherever and it's OK?

I tested the gas consumption of a contract in the jsVM, which showed consistent outputs. I then deployed it to mainnet, and the function calls consume much different amounts of gas. Is the jsVM ...

I am trying to do the reverse action of what I did in this question: Basically sell/swap some arbitrary token and receive ether on Uniswap V2 using IUniswapV2Router02. Here is what I have done: ...

I read over few website, tutorials and answered question here on SE. There is a huge warning about deploying new contract just to store datas. i.e. : bad uint256 public amount; bool public isAdmin;...

I am getting the following error: Error: PollingBlockTracker - encountered an error while attempting to update latest block: Error: project ID is required at C:\Users\myuser\Code Projects\sdfsd\...

I have two libraries: A and B as well as contract C using them. Library B, in one of its functions, needs to call a couple of functions defined for A.Storage. The code below compiles, tests are ...

I'm running a Geth mainnet node. As the size of chaindata is rapidly rising, I moved ancient to an auxiliary HDD plugged in to the same system. Some time afterwards (not sure when, maybe days?) I ...

I am using web3.py. Given a transaction hash, is there any way to determine if a transaction was dropped and replaced by another transaction with the same nonce? Currently i am looping w3.eth....

I am trying to monitor pending transactions with python web3 and an infura node. I am currently using web3.eth.getBlock(block_identifier='pending', full_transactions=True) on a loop to fetch pending ...

I get this error, even though I do specify the transaction sender.Here is my code: for(let a=1; a<TEST_ORACLES_COUNT; a++) { await config.flightSuretyApp.registerOracle({from: accounts[a], ...

I work in a Ropsten testnet. I have a Python application that sends a transaction and returns the transaction's txHash. It is possible to send a maximum of 500 transactions in one request. The ...

Currently I am trying to build private dapp using ganache-cli as a blockchain backend with aws ec2 instance. I get the expected result when ssh from another shell. request: curl -X POST --data '{"...

I want to initialise a two-dimensional dynamic array. For a one-dimensional array it looks like that: function verify(uint[50] memory input){ uint[] memory input_values = new uint[](input.length); ...

I have searched a lot but maybe I am looking in the wrong places. Please how can I get the token addresses for USDC , WBTC and DAI that work with Uniswap Router02 on mainnet and kovan. Thanks

I have been working on a project, where I would like to trace all transactions from a block and for this reason I have been using a fast-syncing node. It works well, the only issue is that querying ...

I created a Factory Contract which can create new ERC20 tokens with the parameters passed to it. Address of the contract: (Goerli Testnet) 0x482829Ba989fBC368F9A89dFf56cdF4036F39F28 I tested the ...

As far as I've known, Ethereum used Proof of Work as its consensus protocol. In the initial stage, the hash power of the Ethereum Network was small, so how Ethereum prevented 51% attack at that time?

I know the logic of using an escrow contract in which 2 or more users send their wagered ETH to a smart contract acting as escrow proxy, and then after some decision contract executes we release the ...

I've a contract that uses an event and I want to share it with a library without having a duplicated definition. The event is in the library, and contract uses it from the library. It works but the ...

Noob here. Was reading this: https://karl.tech/learning-solidity-part-2-voting/ From my basic understanding, a hash function: Receives an input (like x) and spits some result (like y) y is ...

Hello everyone please kindly help me out. I have researched on the error above associated with this block of code. But please is there a way to revise this code so that i can get all the data of a ...

I am trying to buy DAI tokens from my smart contract using IUniswapV2Router02 contract BuyExample{ IUniswapV2Router02 usi = IUniswapV2Router02(...

Im trying to figure out the best way to deploy a contract programatically using ethers.js with web3 I can just do: const contractInstance = new this.web3.eth.Contract(contractObject.abi) var ...

I'm extremely new to Blockchain and mining, and I've followed this tutorial to create my first private blockchain. I am stuck when it comes to mining and I'm afraid I'm quite lost. Afte I've started ...