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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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How to search through blockchain?

I m doing project for document verification using blockchain in which we don't have to carry documents everywhere, hash key of block will fetch data of doc from blockchain.I m not getting how to ...
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Transferring funds from a contract to an account using adresses

I had been trying for a long to transfer the complete fund with one of my contracts to a specific account. But nothing seems to be working. pragma solidity >= 0.4.22; contract reg{ address ...
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How to execute a smart contract only if there are some particular tokens?

i created an erc20 token and i'm trying to create a smart contract that stores some informations in a blockchain and at the same time send a bit of my tokens to a wallet. Is it possible to do? Have i ...
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How do we extract the content of a hash manifest generated by swarm after a download?

As far I know, whenever we upload a file or a directory using: swarm up File we get back a hash that is the manifest containing the uploaded file. However, I am not sure I do understand how to ...
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How Ethereum stores its data in the blockchain

I am new to ethereum and the blockchain, but I am wondering about blockchain databases. Mainly I am wondering how exactly the database data and the blockchain merge. For instance, in a database you ...
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What is the current state of integrating sharding into ethereum? [on hold]

I recently found articles about the topic 'sharding' and how it could help scale ethereum to make it faster in the end. Can anyone tell me what is the current state of integrating sharding into the ...
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Is there multiple chains of block in ethereum network?

Since blockchain is a chain of blocks, In ethereum, 1. is there only one chain of blocks 2. are there multiple chains of blocks.
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How does number of miners impact in processing the business logic(smart contract) in Blockchains

Does a number of validating devices/miners have an impact on processing business logic? If I understand correctly, as the number of validating devices increases, the time it takes to reach the ...
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Saving the actual data vs. hash of the data - which one is better?

I am new to etheruem, I would like to create a smart contract for keeping document data. From 2 designs below, can I know the pro and con of each one, please? put the array of raw JSON data to the ...
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What filesystem should I use for geth and leveldb?

I used old LGA775 machine for running geth node. Its mobo has older sata 3gb/s (benchmark showed that ssd bottlenecked there) and only 4gb of DDR2, with windows installed. So syncing is a real pain ...
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Is it possible to provide some manual data to create private key for the ethereum account?

We were trying to provide some manual data to create the private key if I want to create a new ethereum account using this private key.
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How to store private data on blockchain to be readable from a contract?

I'm writting DApp on Ethereum (Solidity) and I need to find a solution how to store a private data on blockchain, when I also need to proceed them somehow. If it is only about storing, I can use some ...
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Questions about blockchain

I am a newbie with blockchain and I have a few questions please, I've already googled but I have misunderstood some points: How data is stored in the block in blockchain? in bit format, text or other?...
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How to return the struct data

How to return the struct data struct Transaction { address from; address payable to; uint amount; } I am returning like this function transactionDetails() external view returns(...
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Does the ethereum ecosystem exist out of one or multiple blockchains?

Most of my knowledge is based on BTC which doesn't have the concept of (ERC-20) 'Tokens' so I have a question related to that: Does the Ethereum 'ecosystem' with its hundreds or even thousands of ...
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1answer
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How an Ethereum Node stores data?

How an Ethereum client stores the blockchain data in the disk? I know two of the major Ethereum clients is go-ethereum and parity, so I'm also asking if they store data in a different way or if there ...
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Can anyone please help me how can I start with blockchain testing,Deploy application and testing app [closed]

I am completely new to blockchain testing.Can someone please help me with how can I start with blockchain testing and procedure from where I should start and material for the same if possible.
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How secured are private data stored on blockchain?

I'm quite new in Ethereum world and I'm still little bit confused about this: If I store any data on blockchain, is it readable from anyone? Let's say I have this is Solidity: ... string private ...
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is data structures necessary for a blockchain developer?

I want to know if i had to study data structures and algorithms for being a blockchain developer or a smart contract developer
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Transaction submitted through Infura, but not from local node

So, I have a Rinkeby fast sync on my server. When I try to interact with my contract and transfer something, geth says "Submitted transaction", but then I can't find it using its hash on etherscan. ...
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19 views

part of private blockchain disapear

I have a private blockchain, mined by one ec2 instance. When I restart the instance, significant part of the chain disappear with all transaction and contracts on it. How can I prevent this?
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What actually a block contains, is the data inside it a virtual or physical entity?

My understanding of a block in blockchain is that it is a data structure that contains information like Block Size, Block Header, Transaction Counter and then Transactions. Deeper in the Block Header ...
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For Recipient how do I store Sender's account address and Password of Recipient's own account in hashed from?

How to check following things using Solidity: Password matching (hash formed) if password matches then transfer take place
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1answer
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How to prevent modifying blockreward in geth code?

I found below variables in geth file 'consensus/ethash/consensus.go' var ( FrontierBlockReward = big.NewInt(5e+18) //.. ByzantiumBlockReward = big.NewInt(3e+18) //....
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2answers
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What is the main use of approveAndCall() function and _extraData?

function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) { allowed[msg.sender][_spender] = _value; Approval(msg.sender, _spender, _value); if(!...
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1answer
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how to validate and execute an ethereum transaction

I'm confused about how to validate a transaction in Ethereum. In fact, according to my simple knowledge, I know that the transaction row is signed and then the signature of the transaction is ...
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Who hosts IPFS?

I'm trying to get my head wrapped around how IPFS actually stores files. There is no IPFS coin, so who is hosting these files and are they getting paid to host them?
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what is the form of the block stored in ethereum?

I really wonder the form of the block when it stored in Ethereum. Is it the binary file or text file?
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25 views

Key-value immutable storage: on-chain vs IPFS

I'm currently working on a D-App for a client. It's basically a temper-proof immutable storage of 'objects', each object being defined with 8 key-value pairs (strings) and a collection of pictures. ...
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How blockchain verifies the chain's data with the underline implementation of database?

Suppose I have a merkle tree containing the blockchain implementation of a system and I have used databases along with it to do search operations on it. So my question is that how does blockchain ...
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1answer
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What is the main use and purpose of Upgraded Standard Token?

contract StandardToken is BasicToken, ERC20 { mapping (address => mapping (address => uint)) public allowed; uint public constant MAX_UINT = 2**256 - 1; function transferFrom(address _from, ...
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In Tether Token issue() and redeem() functions belongs to which Standard?

function issue(uint amount) public onlyOwner { //_totalSupply + amount must be greater than the _totalSupply value require(_totalSupply + amount > _totalSupply); //balance of owner + ...
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1answer
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Sending Ether between two separate ethereum blockchain [duplicate]

is there any possible way to send ether (preferably other cryptos too) between two separate ethereum (also any other blockchains) blockchains ? also is HTLC support is needed for this to be achieved?.....
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1answer
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Performance Analysis of Ethereum Clients Geth and Parity

I want to do performance analysis of Geth and Parity. I want to run 1000 transactions serially on each client and want to get transaction processing time for each transaction. How can i get these ...
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1answer
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How to concatenate string array into a single string

I am trying to concatenate a whole array of string into a single array for printing purpose. function getArray() public view returns (string) { arr.push("Max"); arr.push("good"); arr....
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1answer
22 views

How can I execute transferFrom function in node js

There is solidity erc865 code function transferFromPreSigned( bytes _signature, address _from, address _to, uint256 _value, uint256 _fee, uint256 _nonce ) public ...
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1answer
25 views

Dataset for Ethereum applications

i am searching for public available datasets from projects, in which the blockchain technology would be "useful". For example projects like supply chainys or trading (e.g. in the energy market). I ...
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What is BlackList and why it is used in Tether Token Smart Contract? And what is the use of Pause and Unpause in Tether?

contract BlackList is Ownable, BasicToken { function getBlackListStatus(address _maker) external constant returns (bool) { return isBlackListed[_maker]; } function getOwner() external constant ...
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Trying to figure if blockchain has finished downloading.

I am working on the text, Mastering Ethereum and working on the part where one has to download the blockchain. Now I elected to use geth because parity seemed to be getting stuck on blocks for almost ...
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1answer
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How do miners claim gas from an invalid transaction?

Suppose a transaction T changes the state from S to an invalid state S'. For example, say, it ran an long loop of no operations (no_op), and attempted a double spend. Since this T transforms the state ...
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1answer
51 views

Asset based transfer Solidity Contract

I am trying to create asset based transfer Smart contract by solidity language. i'm using ethereum. functions are Create assets (land_id, land_size, land_price) with a ownership of contract owner. ...
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Gas estimation failed

whenever I want to run this code I get this error "Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending? VM ...
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1answer
25 views

ERC20- Error encountered during contract execution [Reverted] Transfer Already Created Token

I have created contract on Ropston TestNet which will send any already created tokens. Unfortunately its giving me error Transaction Details Available at: https://ropsten.etherscan.io/tx/...
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1answer
77 views

Solidity Getter and Setter Error [duplicate]

I started my first code in solidity . when i was implemented getter and setter i have face some error . The Following code, pragma solidity ^0.5.0; contract MyFirstContract{ string private name;...
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1answer
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How Ethereum consensus validates same transaction from different miners? [duplicate]

In an Ethereum node, my brief understanding regarding transaction flow is below. When a client initiates a transaction, all mining nodes receives this request. Based on gas price, miner choose to ...
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1answer
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is there any method convert mutiple params to one bytes in web3js ,and then get these original data from bytes in solidity?

eg: the params in js code below,how to convert to one bytes var min=100; var max=100000000000; var price=1000000000000000000000000000; var name="john"; in solidity code below,how to get original ...
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1answer
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Will Eth 2.0 be implemented in geth (go-ethereum) or will it run on a new client?

Geth is the official implementation of Ethereum based on the coding language Go. Currently, there are 8 teams that are building Eth 2.0 https://www.coindesk.com/next-gen-buidlers-the-8-teams-working-...
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1answer
46 views

Data availability in Ethereum/Hyperledger-fabric (Blockchain)

I have a use-case like there is an admin who creates application and invites several user to use that application. Now, i need to audit trail over the activities done by the user. Users no need to ...
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1answer
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Event not visible on Etherscan transaction list

I have a BuyToken event when user send ether to smart contract they will receive tokens based on ether amount. For ex: 1 ETH = 1000 Token. /// This notifies clients about the Buy Token event BuyToken(...
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1answer
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Inspecting IPFS files

Is it possible to store / catalogue every file which is being published over IPFS ? Is only encryption the viable way to securely publish files over the internet ?