All Questions

I am following a tutorial to use oracle from Provable, so I have to import "https://github.com/provable-things/ethereum-api/blob/master/provableAPI_0.6.sol". I notice that the contract is very big but ...

To monitor my contracts during development and test in a private blockchain I’ve written an event explorer that encodes beside other parameter the ABI in an URL parameter. The ABI will be compressed ...

I have a method in contract to increase totalSupply and only owner can call it. function addTokenToTotalSupply(uint _value) onlyOwner public { require(_value > 0); balances[owner] = ...

I would like to sign a transaction from a wallet which is derived from a seed, and sign it, with it's parent first address and private key derived from the seed, can I sign any tx of any derived ...

pragma solidity ^0.4.24; contract test{ uint[] public array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]; function removewithgap(uint index) returns(uint[]) { if (index >= array.length) ...

Need to convert BigEndian to LittleEndian or vice versa.

I have the following code: // SPDX-License-Identifier: MIT pragma solidity >=0.4.22 <0.7.0; pragma experimental ABIEncoderV2; contract VenueRegistry{ struct Queue{ uint head; ...

I have read several articles of off-chain definition and come to know that they are use for scale the ethereum blockchain. but my question is what is actually mean by off-chain word in ethereum ...

I have setup my own private eth network. I wanted to connect to this. So first I have run geth --datadir ./tolotolo --networkid 1115 --port 30304 console 2>>myEth.log It generated geth.ipc ...

Take the transfer function of the DAI contract as example. It allows only two arguments: dst and wad. This is how the decoded data input looks like on a sample transaction: Function: transfer(...

I'm getting the following error during the testing in Truffle: Error: Returned error: VM Exception while processing transaction: revert It simply says "revert" without the contingency message, ...

To create a token on Ethereum, we use ERC20 token interface to design our token smart contract that captures functions required like mint(), tranfer(), balanceOf(), etc. Similarly, do we have any ...

I am reading this article to understand the storage in Solidity/EVM https://programtheblockchain.com/posts/2018/03/09/understanding-ethereum-smart-contract-storage/ It says that each smart contract ...

I know for sure I have enough eth on account. Some prelims: I am signing a raw transaction with web3.py, like so: transaction = { 'to': '0xSENDHEREFINALLYPLEASE', 'value': 1000, 'gas': ...

If I understood correctly, when I want send a token using wallet (e.g., ERC20 token), I will: create a transaction (using send button on my wallet interface) with "to" address containing token ...

I am new to solidity. I was trying to compile the following code in chrome browser with Remix. I am getting the following error "Data location can only be specified for array, struct or mapping types, ...

I am new to web3j and smart contract deployment. Consider a scenario where a user is too scared to give his wallet credential file or username/password or private key in a piece of code(the code is ...

I am trying to create a simple role based access control system for the contracts I have created. I have two smart contracts, one named Users that stores all of the users details as well as the type ...

I am doing a research project which requires me to implement a blockchain with pBFT consensus algorithm. The blockchain would be very simple - A client should be able to send 2 values, the validators ...

I'm running testrpc on the default port 7545. I run truffle console and test with: web3.eth.getAccounts().then( function (result) { return result[0] }); This works fine. According to docs the ...

I created ERC20 compliant token on Ropsten testnet. I set in constructor that all of the token supply is added to my wallet address. When I open the metamaks I see that I have the tokens. Here's the ...

I am working on the elliptic curve and pairing stuff in Ethereum smart contract. How can I compute pairing such e(p1,p2)? I know that we have a pre-compile pairing check in Ethereum client which is ...

Could you please enlighten me on how approve and allowance functions work using a usecase? I dont understand the underlying operations of these functions. Especially, when a token owner delegates the ...

Firstly, thank you for helping me out in understand this. Suppose, if I have an ERC20 token contract (with all the required functions implemented including Transfer() function) deployed on the ...

When sending eth_call to get erc20 token WETH name and symbol I get hex response padded with bunch of zeros and a mysterious digit '2'. for symbol I get response: "...

I'm developing an application on a private Ethereum chain and trying to listen to some events. I wrote a basic indexer script for listening to events and writing them in a database. To listen to the ...

The ERC721 standard contract requires a token name and symbol in its constructor. I have inheritance pattern that looks likes Contract A is B and Contract B is ERC721. If I want to set my token name ...

It took 2 days to get to 200gb on geth fast synch mode. But now im moving with approx 5gb a day with a decent internet speed around 100mb/s in Lan. I disconnected and now running on 25mb/s with wifi....

The following code is part of a Smart Contract I'm working with: [...] function noComplain() allowed(receiver, stage.keyRevealed) public { selfdestruct(sender); } // function ...

The Schlesi testnet was the first multiclient testnet for ETH2 clients. Lighthouse, Prysm, Teku were in consensus before it forked. What were the causes of the forks? Is there a technical post ...

I have set these paths but not working C:\Program Files\Ethereum-Wallet and C:\Program Files\Geth I have made a private network using Geth, but when I installed the Ethereum Wallet, it is not ...

when implementing ERC721, why it is necessary to use ERC165 standard? `pragma solidity ^0.6.6; interface ERC165 { function supportsInterface(bytes4 interfaceID) external view returns (...

I am trying to install and use python solidity parser by ConsenSys I keep on getting the following error File "<stdin>", line 1, in <module> File "/home/seed/.local/lib/python3.5/site-...

As far as I understand, a private key in the context of Ethereum is simply 256 random bits. The actual application of secp256k1 comes in when converting this to the public key, signing, etc. Based on ...

Let's say I have two light nodes on a chain and I want them to exchange data ~3KB without appending anything to the chain. They are not on local network. How can I achieve it?

Below is a contract that i have commented on, hoping to understand the logic of the arguments. Below in bold is the question in question. The .sol currently works fine. pragma solidity ^0.5.11; ...

would like to build a blockchain simulator with web3 interface. I use ganache and solidity. my simulator is a microgrid simulator (autonomous energy community) where a house is represented by an eth ...

i'm doing some research about Ethereum 2.0 for university. I think i understand the way it works, but i have a perplexity about the proposer selection in a slot, especially after reading the codes ...

I am trying to generate a bytecode to deploy a contract to ethereum. I have included node.exe as resource and try to install solcjs programmatically in node, but unfortunately i am stuck. My current ...

How to determine the uniqueness of an internal transaction Example is this transaction: https://rinkeby.etherscan.io/tx/0xc756517a69239bddffe3e0cb07eba98d3ad0fae1b44fc936a0119dbaf7008942#internal ...

I have a smart contract with a custom token which holds some data. The Token data is defined in a struct and stored in an array: struct Token { string text; uint256 value; } Token[] public ...

News Chainlink announced a randomness oracle via VRF: https://blog.chain.link/verifiable-random-functions-vrf-random-number-generation-rng-feature/. Question What is the advantage of an VRF over a ...

Does Ethereum 2.0 (Sharded Ethereum) only use PoS (Proof-of-stake) for consensus mechanism ? Or Does it use a combination of PoW + PoS ?

I deployed an ERC-20 Token contract and would like to now verify it on etherscan.io My contract utilizes Open-Zeppelin's library of contracts - which means it's importing one of their contracts into ...

This question is regarding the bytecode-optimizer of the solidity-compiler, not the yul-optimizer: Is there any way to separately optimize bytecode? Normally the solidity-compiler optimizes the ...

I have an error when building a private blockchain on my computer. The code that I run is like this (Simply my concept make it without mining and only focus on smart contract): genesis.json file { ...

I have a program that can get me the first part of registered blockchain domains, but not the suffix (.eth, .zil, etc.) and am not sure how to associate suffixes with names. I know that in some cases, ...

I just started dabbling in running my own light node and it seems like the biggest challenge is finding peers. rfikki on GitHub posts these peer lists (https://gist.github.com/rfikki/...

What is the has() function in Solidity? struct Role { mapping (address => bool) bearer; } function add(Role storage role, address account) internal { require(account != address(0), "...

I am able to get gas price data as follows from some oracles (i.e., ethgasstation.info, etherscan.io): { "fast":50.0, "fastest":200.0, "safeLow":10.0, "average":20.0, "block_time":13....