Questions tagged [blockchain]

The Ethereum blockchain is a distributed database based on the Ethereum whitepaper specification and stores both the full transaction list and the most recent state.

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9 views

Characterization of behavior on the network

I'm starting a new research using characterization and would like some ideas of interesting topics over the Ethereum network that can be achieved by looking at the blockchain data itself. Any ideas ...
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How to change push() method to simple code?

I have this code but it's static and I wanna change it dynamically. function addCandidates(){ if( own == 1 ){ candidate[0].candidate_ID[0] = 1; candidate[0].candidate_ID[1] = 2; ...
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Quorum-maker-node not starting

I have created a node in quorum-maker using my ip address but that node is not starting.If i create a node using local ip(127.0.0.1), node starts.why?
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Arduino Vs Raspberry pi with Ethereuem Blockcain

I already built a smart contract for Ethereum Blockchain by using truffle to track the ownership of IoT devices; Now, I'm looking to connect my smart contract with the IoT environment (node) to detect ...
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Are there any virtual IoT simulators that facilitate the connection with Ethereum Blockchain?

I already built a smart contract for Ethereum Blockchain by using truffle; Now, I'm looking to connect my smart contract with the IoT environment. So are there any IoT simulators (platform, framework,...
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Can we connect custom Ethereum currency through java's web3j library ? If yes then how?

Im trying to create my own new currency using solidity and ethereum platform and also i want to create an Ewallet of my currency using java so that my ewallet could communicate through api .If u ...
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Why do I always get “Returned values are not valid, did it run Out of Gas”?

I'm new on Ethereum blockchain and I'm working on deploy and using smart contract using truffle on my private blockchain. I have followed exactly this guide https://www.trufflesuite.com/docs/...
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Linked contracts not running on go-ethereum

A very simple linked contracts example where A contract has a variable and B contract queries the A contract's variable is running ok on Ropsten+myetherwallet and Remix sandbox, but it fails when ...
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Why my smart contract's function always return 0?

I'm new on Ethereum. I'm trying to deploy my first smart contract in my private blockchain but my function always returns 0. I wrote the simple Smart Contract: pragma solidity^0.5.0; contract ...
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Is QTUM is a coin or a Token?

According to Etherscan Qtum is a Token, holding supply with verified smart contract. But its official site contains its own protocol and integration mechanism. Is it still a token under ETH or it has ...
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How to find out in blockchain ledger the current ownership of asset being transacted

I am new to blockchain and smart contract as well. In smart contract we can only save the current state of any transaction but if we need to know the previously expunged transactional data ie, the ...
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How simulate blockchain and smart contract in VANET?

I am a beginner in the blokchain, I am blocked how I start simulate a blockchain and smart contract in vanet. Can you help me and inform me how I have to simulate blockchain and smart contract in the ...
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validation of data integrity in block

I am learning ethreum dapps development and have developed some dapps. I was thinking about supply chain dapp which i think , is very good application of blockchain as it ensures all the history of a ...
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How Merkle Patricia Trie updates the account balance?

This is my understanding of the Merkle Patricia Trees in Ethereum so far: There are three kinds of merkle trees storing diff info - state, transaction and receipt. When a new block is added it ...
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How to transfer ERC20 token from one account to another account but paying the transaction fee from third account?

I want to transfer token from account A to account B by paying transaction fee from account C.I have tried the following logic but token transfer from contract to contract mean contract transfer token ...
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Failed to read genesis file: open genesis.json: permission denied

First of all I have to say that all this things will work on my windows machine. Today I started to do the same things on a ubuntu machine (with ssh and private key authentication). I've created a ...
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How to build an ethereum based wallet with custom UI?

I have been interested in ethereum for quite some time now and have always wanted to learn ethereum development. I decided to create my custom erc20 tokens i was able to create 2,00,000 tokens. Now i ...
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How to download the blockchain of a single ethereum contract’s address?

The blockchain required to run ethereum is several Terabytes large. This means more than 9 years would be required to download it with my connection speed. In my case, I just want to know if the ...
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Why is PoW needed to confirm transactions and add new blocks

I have read and I vaguely understand about how Proof of Work works and what does it do. But why PoW? Or more bluntly, why do we need any algorithm at all to add new blocks. What would happen if ...
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Exchange ERC20 token with other ERC20 token

I have 2 ERC20 tokens. The contract are designed as standard ERC20. Here are the 2 tokens to take as an example - AUDC --> Contract Address: (0xContractAUDC) Wallet Address: (...
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Blockchain Development [closed]

I want to build a blockchain network such that if one node updates, all the other linked nodes gets update too. Think of it as Centralized Hospital record in multiple cities, if any of the city pushes ...
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web3.exceptions.BadFunctionCallOutput: Could not decode contract function call getEvidence return data b'' for output_types ['string']

Solidity Code: function getEvidence(string memory _evidenceID) view public returns (string memory) { require(evidenceOwner[_evidenceID] == msg.sender); string memory evidenceHash = ...
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Create2 and new contract deploy at used address

Given that it seems possible, using somehow CREATE2, to deploy a new smart contract at a certain address where a different smart contract existed before to be killed... (see @smarx answer here Can ...
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Can you use a private Ethereum blockchain network to deploy an actual application for the public?

I am starting to do some research for my blockchain based project and I was wondering if it is possible that I can deploy my project on my very own private ethereum network for actual public use and ...
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How is Ethereum Virtual Machine (EVM) isolated (sandboxed)?

I always had this question in mind: What are the used technologies, in order to achieve the isolation of the EVM? does it just run as an isolated process in its own namespaces using the linux feature ...
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Is Egretia (EGT) is still Ethereum Token? Or It has been moved as a Coin to its own Blockchain?

Currently Egretia (EGT) is represented as a Token of Ethereum Network, but is there any changes regarding shifting from Token to Coin on its own Chain?
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cannot be able to connect to private blockchain hosted at local VM

I want to use remix IDE and want to connect web3provider which needs to be connected to private blockchain running on VM locally. My system is running on Windows 10 and I am running the VM on my local ...
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Web3 - how to add WEI and ETH values correctly

I'm working on an auction feature in my DApp and having problems correctly adding together two WEI values. The contract stores two important values: 1. A minBidIncrement variable - which I've set to ...
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Useful resources to help understand go-ethereum source code

I am new to ethereum community and I want to study the implementation of Ethereum (e.g. geth) and contribute to the go-ethereum project. However, I find the source code hard to understand by only ...
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160 views

MetaMask - RPC Error: Internal JSON-RPC error

I am getting this error when i trying to use metamask on my local for a simple transaction from one account(say A) to another (say B). code: -32603 data: {originalError: {…}} message: "Internal ...
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22 views

How to match the data in the struct?

If the Set function receives two inputs 1.["0xca35b7d915458ef540ade6068dfe2f44e8fa733c",50,"ROC","park"] 2.["0x14723a09acff6d2a60dcdf7aa4aff308fddc160c",60,"AU","school"] How can I return all the ...
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Can we treat/launch private ethereum chain ethers as a CryptoCurrency in Market?

Warm Greetings! I have a private ethereum blockchain setup on my server with multiple nodes , Also running mining software to mine blocks and earning private ethers (no value in market). Can i ...
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Is there a way to prevent your smart contract from burning ETH, and sending it to your wallet instead?

So I am writing my own smart contract on remix.ethereum.org, and it is for a token, and in the code, I have written a simple ICO: function() public payable { if (totalSupply >= 1000) { ...
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How do I deposit an Ether amount to the smart contract function, namely deposit ? (Metamask version 0.20.7)

I have a problem with using the deposit () function on a smart contract. How do you use metamask 0.20.7 ? const contractInstance = web3.eth.contract(contractAbi).at(contractAddress); contractInstance....
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Can I call someone else's public function/contract

Still new and learning. Forgive me if this is a stupid question. Since all contracts are uploaded to the same blockchain, if I wanted, could I use someone else's public contract in my own front-end ...
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1answer
21 views

Two smart contracts interact can't pass value when I using web3.js

I have two different smart contracts interaction_1 and interaction_2 I input the data(team) from remix ide. What I want to accomplish is when user input team in user_input function at interaction_1,...
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In ethereum network how data structured and is every data stored, is public?

Let's say, 3 companies are using ethereum network. Company A Company B Company C Company A put some data, block01 and block02. So ethereum network looks like, Genesis Block -> block01 -> block02 ...
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How to print the value of a Struct ?(mapping)

If the set function receives two inputs 1.["0xca35b7d915458ef540ade6068dfe2f44e8fa733c",50,"ROC","park"] 2.["0x14723a09acff6d2a60dcdf7aa4aff308fddc160c",60,"AU","school"] How do I display the ...
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35 views

I Call SmartContract Token ERC20, Why Show Hashing Output ? (Web3 + Metamask + Javascript)

I do not know why with this, even though in the previous version (web3 + Metamask) can issue real data. But now used as hashing (output). I took the example in the code and output below (to get the ...
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3answers
119 views

How smart contract transactions work?

I read that smart contracts don’t have a private key, so they can’t sign a transaction. My question is: when a smart contract starts a transaction to an EOA, how are we sure that the smart contract ...
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How to deploy a DAO on Ethereum?

Want to deploy and operate a Decentralized Autonomous Organization (DAO) on Ethereum. What are my options?
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How to build a decentralised Voting Website without using any 3rd party extensions like Metamask, or IDEs like Remix? [closed]

I've gone through various Blockchain Tutorials but everywhere it's one or the other same thing. Download truffle/ganache, from 10 free testrpc account, use one, use metamask, Remix IDE etc, and Voila!...
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Ethereum as a private network is possible? [closed]

can i deploy a private network like the way it does other private blockchains with Ethereum ? and the test networks in Ethereum only work for public right or can i deploy it there ?
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How to build the seamless bridge between two blockchain platform?

How to build the bridge between two different consensus blockchain platform? use case: 1.we need to ensure visibility of the transaction in both platforms to assure its integrity When a smart ...
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1answer
30 views

About send Ethereum Classic (ETC) coin

Need guideline for send ETC coin using web3js,As per documented flow I understand we can access all methods same as ETH but I have query regarding set provider for ETC after that I can connect to ETC ...
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Fatal: Account unlock with HTTP access is forbidden! [duplicate]

I'd been following a tutorial about How to make your own local blockchain, everything was fine until i shoould run the next script: geth --networkid 22773 --mine --minerthreads 1 --datadir "~/home/...
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Migrate Database

I want to migrate my no-SQL dB on-chain. There are two options as far as I know: Store the objects in the form of string using a simple smart contract. Create a structure to implement the dB schema. ...
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Can we pass string values to the contract which holds bytes 32 only in solidity?

My contract can hold only array of type bytes32 only. How can we store string values as well?
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Contract address is not shown in rinkeby testnet etherscan

I am using Getch with truffle framework and i created an account. I have Migrations and Election.sol. After i can migrate, i couldnt see it in etherscan website. Although truffle migrate --reset --...
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Gas required exceeds allowance truffle migrate

Hi i am trying to work truffle migrate and firstly it start to Migration.sol and then Election.sol. When start to deploy ELection.sol it throws following error. What should i write gas:270000 instead ...