All Questions

5
votes
1answer
34 views

What is WETH and why can't we just use ETH?

can someone explain why we need WETH? what's the purpose of WETH, can't we just use plain ETH? it's not like it removes the tx fees or something. Hopefully someone can shed light on the concept.
0
votes
0answers
12 views

Load smart contracts in Java application without having the java wrapper class for Web3j (only the address of the contract)

I use web3j to interact with my local Ethereum node (created with geth), and I was wondering how should I handle smart contracts created at runtime. I know that in order to deploy a smart contract ...
1
vote
1answer
30 views

Invalid Opcode opcode error

I keep getting Invalid Opcode opcode in my constructor when deploying my smart contract in both truffle and remix IDE mapping(address => bool) isMintApprover; uint minApprovers = 0; address ...
0
votes
0answers
69 views

ETH wallet error

I want to download the ETH wallet and make light synchronization on my PC. I downloaded ethereum wallet, but after launch, the Checksum mismatch in downloaded node crashes! MD5: 308 ... Please install ...
0
votes
0answers
14 views

- does not trigger a Solidity `revert` statement

My Smart contact was running smoothly .I was smoothly executing the function successfully . MinterFunction(address account, uint256 value) public { value = value.mul(1 finney); require(...
2
votes
3answers
35 views

How to generate an ethereum address?

How an EOA, contract address can be achieved? What is an mechanism for generating these?
1
vote
1answer
97 views

How to prevent selfdestruct from another contract

I have a contract A calling another contract B Contract A contract A { function sendValue(B _externalContract, uint _value) { _externalContract.acceptValue(_value); } } contract B { ...
1
vote
1answer
25 views

How to save new account in ganache-cli

I use ganache-cli --db to create a private test chain and save it on my computer, and the result is below: I use web3py w3.personal.newAccount('1') to add a new address, and I use print(len(w3....
1
vote
0answers
23 views

How long did a transaction spend in the mempool?

I'm trying to create some statistics on how long a transaction spends in the mempool before being included in a block, so I can reason about future gas prices. It would appear transactions in Ethereum ...
1
vote
1answer
14 views

Return each struct value from a key inside a mapping, where the key is also a value from array inside another mapping

I have a project that I'm working on and I'm trying to figure out a way to do as the title says. I'm looking for the easiest and/or cheapest way(gas wise) and since I'm stuck I'm open to better ways ...
1
vote
1answer
18 views

Listen smart contract event

I use parity --light geth --syncmode "light" I would like to listen smart contract Event. Do I need to download all blockchain on local PC or light mode will be enough?
1
vote
0answers
8 views

Invalid JSON RPC response on IOS build with Infura

I am developing a mobile DAPP using ionic frame work, everything was fine when I testing on the browser. However I try to build my app on IOS, and run it on my Iphone7, the web3 doesn't work(did't ...
0
votes
1answer
18 views

This declaration shadows an existing declaration

When i try to run migration from truffle, i got this problem, here my contract code: pragma solidity ^0.5.0; contract DappToken { uint256 public totalSupply; function DappToken () public ...
0
votes
0answers
7 views

Is it possible to do vote and participate in crowd-sale using Forwarder address?

Currently, I am using Metamask (Ropsten TestNet). And I want to implement one voting cum crowd-sale process, the scenario is given below: Want to make the voting process in this if Voter is voted to ...
1
vote
2answers
26 views

Decentralized Exchange on Ethereum?

Is a decentralized exchange basically a smart contract that includes all the exchange functionality? Where is the engine?
0
votes
0answers
14 views

Send ether from one wallet to another

I have two metamask accounts and what I want to do is send ether between those accounts. For the interaction between those accounts, use infura, I give the address of both accounts but in the end the ...
0
votes
0answers
12 views

Etherscan apikey error in laravel

Etherscan apikey returns an error This is my code: namespace App\Http\Controllers; use Illuminate\Http\Request; use App\Models\AdminSettings; use App\Models\User; use Auth; define('APIURL', 'http:/...
2
votes
1answer
14 views

Any other provider instead of Oraclize

Are there any other providers for calling external APIs in Solidity other than Oraclize?
-1
votes
0answers
35 views

How does a smart contract make block chain?

My question is about the procedure in which a smart contract makes blockchain. I mean if the hash chain is made just by actions in a smart contract or all actions in Ethereum platform? If T(1) is the ...
2
votes
1answer
20 views

What is the purpose of Görli Testnet?

Görli testnet is started with the goal of being widely usable across all client implementations supporting Clique PoA engine (EIP-225) (see Comparison of the different TestNets) Since it exists ...
0
votes
1answer
18 views

Etherscan how to get latest transactions?

I am using this api to get all transactions at an address, however I see it returns the last 1000 transactions, is there any way to make it return first 1000 transactions by date?
0
votes
1answer
22 views

How to assign value to function(transfer) 's parameter

I use these codes(@Lauri Peltonen ) however I tried 5 ether and 500, but I found it had an error in remix " like I need to add payable to constructor, but I already added". What does that mean? ...
1
vote
2answers
39 views

Decode transaction input INSIDE contract with solidity? [duplicate]

I would like to know if it is possible to read blockchain transactions from a smart contract. How web3 has the possibility to scroll, read and decrypt the input data of the transactions, does solidity ...
0
votes
1answer
17 views

Problem in contract verification through EtherScan API

Contract source verification through these APIs is putting it 'pending in queue' and not getting confirmed. This interface is also behaving same. I tried it with rinkeby and kovan. Here it works ...
2
votes
2answers
24 views

Create multiple tokens and manage multiple wallets from the platform

I'm new to blockchain and Ethereum, I currently started researching about to work on a new project. I wanted to ask for advice on what should I use or what it will fits better for my use case: In my ...
1
vote
1answer
20 views

Will ERC223 Tokens work after Serenity Update?

Trying to understand what we should expect after External Owned Accounts will be treated as Contracts after second Serenity update will be live. How does it influence ERC223 Tokens, will they break ...
-1
votes
0answers
29 views

VM Exception while processing transactions

I am testing a smart contract with three contracts, an escrow, another for processing entities called industry and another for consumers.Everything works. However, when testing with truffle, I ...
0
votes
1answer
28 views

web3.js - cannot interact with smart contract

I want to write a simple js script. I follow many tutorial available from Youtube, forums and website but i seem that i cannot interact from the smart contract. i can interact it from remix. btw the ...
1
vote
1answer
22 views

Why gas price so high in erc20 tx?

I know normal gas price is 1gwei(https://etherscan.io/tx/0x4b0aaea87288a1080288187d99c666749577801014535f879d5d85719866ddeb). But why transaction in erc20 is 6gwei or 30gwei (https://etherscan.io/tx/...
0
votes
0answers
13 views

Is S of the signature(R,S) invalid when it is larger than N/2 in Ethereum?

In ECDSA, both signature(r,s) and (r,-s) are valid. However, in Bitcoin, it seems that the signature fails to be verified when s-part in the signature is bigger than half of the group order from this ...
3
votes
0answers
9 views

Create a slightly customized version of ethereum and run it as a node on a public ethereum blockchain

I might need a small modification to ethereum virtual machine but I still want to run it as a node on the public blockchain not private, if that makes sense. I assume its doable? Since I will not be ...
1
vote
2answers
20 views

Constructor should be payable error on adding money

pragma solidity ^0.4.17; contract supplyChain { address public state; uint public unitCost = 10; uint public totalAmount = 0; function supplyChain() payable public{ state = ...
0
votes
1answer
25 views

Why Ether balance is 0 after 5 airdrops?

I created an ether wallet to join some airdrops and 5 of this airdrops sent me tokens but in my ether wallet the balance is 0 (zero). I don't understand why. I was searching tutorials but I could not ...
0
votes
0answers
24 views

How do I call my smart contract functions through web3 js?

So I am very new to Blockchain development so sorry in advance! I have deployed a very basic Smart Contract to the Ropsten testnet. I am developing a front-end and from here, I want to withdraw ether/...
1
vote
1answer
24 views

How to have users sign transactions on an ethereum based platform without giving up their Private Keys to the platform?

How to have users sign transactions on an ethereum based platform without surrendering their Private Keys to the platform? Need the process to be automated, while users not giving up their private ...
0
votes
1answer
11 views

Solidity, how to cast SmartContract type to address

I am currently a bit stuck with my contract, the issue is following: I define a smartcontract type which is used for another address (aka address is smartcontract that provides the specified interface)...
0
votes
0answers
25 views

How to create an ethereum private network with proof of authtority without gas cost or gas price zero?

I want to create a private network but I don't need to use ether or gas, only I want to run smart contracts and the blockchain using ethereum technology. I find this tutorial Private proof of ...
1
vote
1answer
27 views

How to prevent the code of my contract being used in a CALLCODE?

Simple question but I couldn’t find the answer anywhere. How to know if the code of my contract is used in a CALLCODE or DELEGATECALL by third party sinceaddress(this)returns the address of the caller ...
0
votes
1answer
9 views

ERC1820 interfaces State variable

I have a question related to ERC1820 : Pseudo-introspection Registry Contract in the offical link (http://eips.ethereum.org/EIPS/eip-1820) in ERC1820Registry implementation contract what is the ...
0
votes
0answers
17 views

Facing issue in starting geth client

I am using geth client(private network). When I try to start my network it shows "segmentation fault". Can you guide how to solve this issues? go-ethereum/build/bin/geth --mine --nodiscover --...
0
votes
0answers
16 views

what is the standard server configuration for hosting own kovan validator node?

What is the recommended hardware specifications ( CPU, RAM, Network ) to host my own validation node for kovan testnet and what is the average data transfer out from validation node?
1
vote
1answer
105 views

Zepplin Proxy Code Pattern

I am trying to understand the Zepplin proxy code pattern so i deployed two contracts using remix Token.sol (logic contract - basic ERC20 contract) AdminUpgradeabilityProxy.sol (From zepplin) https://...
2
votes
0answers
11 views

Most efficient way to get all non-zero storage locations for a smart contract?

I'm looking at a mainnet smart contract and want to figure out all storage positions/slots where the storage has a non-zero value. Is there a way to do this other than replaying and tracing all ...
0
votes
1answer
40 views

invalid opcode “0x1c” during smart contract method execution

I have written a smart contract to test event from java project using web3j I have prepared the web3j wrapper java class using solc compiler version "0.5.7+commit.6da8b019.Linux.g++" I am using a ...
3
votes
1answer
38 views

How do I extract the v, r, s values from a signed transaction

If I have a signed transaction such as ...
0
votes
1answer
25 views

Externally Owned Account use Contrast account to transfer ether

can I use a Externally Owned Account to call contract account function to transfer ether to other Externally Owned Accounts, and the ether is from contract account.
1
vote
1answer
22 views

Truffle Ropsten Deployment Issues

I just made some updates to my contracts and tried to redeploy them - but I'm getting this message, over and over again. Its not even attempting any of the migrations - it just goes right to this ...
0
votes
1answer
23 views

Using AbiEncoderV2 for encoding data in raw transactions

I've come across a use-case to need to pass a struct into a Solidity function. I know this can be done via tuples. However, I need to sign and send this transaction from my node.js back-end using ...
0
votes
0answers
15 views

call() returning BadFunctionCallOutput in web3.py

Have a very basic ERC721 contract based on OpenZeppelin-Solidity, as follows: pragma solidity ^0.5.7; import 'openzeppelin-solidity/contracts/token/ERC721/ERC721Mintable.sol'; import 'openzeppelin-...
1
vote
1answer
18 views

Database connection with smart contract

I am developing a Dapp, which has a smart contract in solidity and uses truffle framework. My smart contract has a constructor that takes a value as an argument I want to initialize this smart ...

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