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.

Filter by
Sorted by
Tagged with
0
votes
0answers
4 views

How to create blockchain nodes locally

For educational purposes I am implementing a blockchain from scratch without the use of any frameworks. How would I go about testing my blockchain using multiple nodes when I only have access to one ...
0
votes
0answers
20 views

Migrating 2 contracts in one Contract.sol script using 'truffle migrate'

I have 2 contracts in 1 .sol file and when I run 'truffle migrate', it tells me that it has deployed 1 of the contracts and given me an additional error: Blockquote Invalid number of parameters ...
1
vote
1answer
36 views

How to kill a contract in ethereum?

I'm trying to kill this contract /** *Submitted for verification at Etherscan.io on 2016-08-31 */ //sol Wallet // Multi-sig, daily-limited account proxy/wallet. // @authors: // Gav Wood <g@...
0
votes
2answers
23 views

Token Sale Smart Contract

I am new to Ethereium Block Chain and have been trying some code written in solidity as follows. pragma solidity ^0.5.0; import "./MyERC20Token.sol"; import "./ERC20Burnable.sol"; contract ...
0
votes
2answers
25 views

Etherscan says there is not enough ether, why?

Etherscan says there is not enough ether, why? Arguments, which i enter => requestLoan(3,31,3) and after change account, provideGuarantee(0,3) I have created dApp and how it looks in my code you can ...
0
votes
1answer
15 views

Smart contracts, tokens and ether

I am sending some ethers and tokens to my smart contract. So how will the contract differentiate between ethers and tokens? Code will be helpful
1
vote
0answers
16 views

Are there more important “impossible triangles” aside from CAP theorem, FLP impossibility and Zamfir's triangle?

I have come across CAP theorem, FLP impossibility, and Zamfir's triangle ever since I began to study blockchain. As I interpret CAP theorem as the tradeoff between consistency, Availability, and ...
0
votes
0answers
19 views

Where's a contract storage stored exactly and how does it interact with the blockchain? [duplicate]

From what I've understood a contract is a special account that gets initialized with a 256 bit array and this array is stored as the root hash of a merkle tree, is that correct? But where is this ...
1
vote
1answer
26 views

What happens in a 50% Attack

I thik it is kind of clear to me that of 50%+1 attack, but now i am thinking about something that occurred when i was testing a DAPP in a two node network. Each node had a blockchain (the same ...
0
votes
2answers
31 views

how transaction in block-chain is validated

Please explain complete procedure/journey how transaction in block-chain get validated by miners, From broadcast of transaction to become part of new block.
1
vote
1answer
22 views

Understanding Transaction in Bitcoin [closed]

I read a lecture about Bitcoin Blockchain. As shown in the slide below, a user Alice sends a transaction to BoB. Alice should 1-) Hash(Hash of the transaction of the coin || Bob Public Key || Alice ...
1
vote
1answer
25 views

Solidity error message on compilation (DeclarationError: Identifier not found or not unique. using Address for address;)

I'm trying to compile a code for a crowdsale contract (Timed and with allowance) from openzeppelin library that is based on a deployed token. However during compilation on remix i get a syntax error ...
0
votes
2answers
25 views

Sending data outside the blockchain

Once a transaction is committed to the blockchain is there a way to let an entity outside the blockchain (i.e. An entity that is not a node in the blockchain) know that a particular transaction has ...
0
votes
0answers
33 views

Error: gas required exceeds allowance (8000000) or always failing transaction [duplicate]

I deployed a test ERC20 to a private ethereum blockchain. It deployed fine because I can get the transaction receipt, see the logs and everything looks ok as far as I can tell. However, when I try to ...
0
votes
1answer
29 views

Architectural blockchain adoption possibilities

I am working on a new shipments management project which will need the blockchain technology to certify the app-generated documents. I have no prior experience in blockchain and after a deep browsing ...
1
vote
2answers
23 views

Ethereum Miners and Gas - Analyzing Chain Data

Currently looking at https://medium.com/google-cloud/how-to-query-balances-for-all-ethereum-addresses-in-bigquery-fb594e4034a7 and in the SQL Query to calculate address balances there is a part for ...
0
votes
1answer
36 views

Store and Display the Json file in Blockchain

I have stored my data on firebase, and taken as a JSON file, the JSON should be separated and display into the webpage through the Ethereum blockchain, for example: { product: "Shoes", prize: "85"...
0
votes
2answers
24 views

What triggers a transaction to be recorded on the Blockchain?

I am new to blockchain development. I am trying to understand where, when, and how a transaction is sent to the blockchain to be recorded. Here is the sample code I am studying: pragma solidity ^0.4....
1
vote
1answer
42 views

Why do transaction receipts not include the value of Ether transferred?

I'm writing some logic to identify the currency used in an ethereum transaction, and am wondering the following: web3.eth.getTransaction returns a value field that indicates the value transferred in ...
0
votes
2answers
32 views

How to find the coin/token type of crypto payer in Ethereum blockchain?

I'm new in Ethereum based crypto concepts. I would like to know how can I differ the incomming crypto amounts based on their orginal token type? Imagine I have an address on Ethereum blockchain. ...
0
votes
1answer
48 views

Ropsten Blockchain Size on Disk December 2019?

Hello what is the size of the Ropsten Blockchain, on disk, using Parity with full trace on? (Info required to provision a VPS).
1
vote
1answer
22 views

How can i store a Aces High Pin on the Ethereum blockchain? [closed]

I have a few Aces High Pin's laying around and wanted to know how i can store them on the Eth blockchain.
1
vote
1answer
47 views

How could return events of specific args?

In my solidity contract, I just have one event which is: transferOwnerShip (uint id, address indexed newowner); and I want to filter the events log in order to retrieve only the events that belong ...
0
votes
1answer
19 views

Return a value from send function [duplicate]

Hi guys i have one really big problem. I have this pice of code function showInfo(uint _pesel) public onlyMainPerson(msg.sender) returns (string memory, string memory) { string memory x = ...
3
votes
1answer
40 views

Can not call the solidity smart contract function from web3js

I am trying to call a method in solidity smart contract through angular app, but I am getting this error: TypeError: this.contract.methods.hello is not a function at CertificateContractService.<...
0
votes
1answer
24 views

all erc 721 tokens being collectibles

Considering all NFTs are unique, are all erc 721 tokens collectibles? I'm asking this because on the Etherscan website some NFTs have the collectibles tag and some do not.
-1
votes
2answers
29 views

Why EVM blockchain can't beat the credit card system in E-commerce [closed]

I want to know, is the blockchain really a success? If its a success why are we still using credit cards? Somebody please guide me why blockchain technology can't prosper? Zulfi
2
votes
1answer
33 views

Blockchain overhead - general question

I was reviewing the blockchain technology the other day, Maybe this is not the right place or maybe I should rephrase my question but.. Blockchain is peer to peer, every peer stores the data Data is ...
0
votes
0answers
27 views

Retrieving the first and latest transaction date of a contract

Etherscan offers a time series of ethereum transaction of a contract address. Is there a way to retrieve this data? For example the duration mentioned here https://etherscan.io/address/...
0
votes
1answer
30 views

How to store data on ethereum blockchain WITHOUT IPFS

Hi guys ^^ i want to store PDF file on ethereum blockchain without use of IPFS. I want to do it because i have my own private network where this data will be only stored. That's why i want to store it ...
0
votes
1answer
43 views

Smart Contract deployment failed

I am making my project of BlockChain subject. I am having a problem with deploying smart contracts. Can anyone help me with this error I have tried everything I could but still failed to resolve this ...
0
votes
1answer
16 views

If you need a server to store HTML and java script code, then what is the use of the block chain?

I have been studying block chain for a while, and I came to know that decentralisation of data is its greatest pros. From my understanding, if block chain is massively adopted in the future, we will ...
0
votes
0answers
44 views

Api to get total transfer count of an ERC-721 Token

I want to retrieve the total number of an erc 721 token's transfers/ transactions. I couldn't scrape the transfers value from etherscan as well e.g. given here https://etherscan.io/token/...
4
votes
3answers
273 views

Do testnets ever merge with mainnets?

Does a testnet ever merge with the mainnet? In other words, if I have ETH on a testnet, will I ever have actual ETH or do testnets remain for testing forever? I Googled in multiple ways but could ...
0
votes
1answer
21 views

How can fix in smart contract written in solidity?

TypeError: Invalid type for argument in function call. Invalid implicit conversion from address to address payable requested. selfdestruct(admin); pragma solidity >=0.4.21 <0.6.0; ...
0
votes
2answers
72 views

How can Ethereum sustain short block creation times if the uncle transactions are not counted?

Lower block times are clearly desirable. Why does not Bitcoin reduce block creation times to 15 seconds just like Ethereum in this case? Because it would lead to too many forks. The main problem with ...
0
votes
0answers
50 views

Unable to Unlock Account Even After specifying allow-insecure-unlock

Software: Ubuntu on VirtualBox Update, tried putting two dashes, on allow-insecure-unlock, doesn't work solidity@solidity:~$ geth attach http://127.0.0.1:8545 --allow-insecure-unlock Incorrect Usage:...
0
votes
1answer
41 views

How does the reentrancy attack work?

Consider the following contracts contract Victim{ //... function donate() public payable { credit[msg.sender] += msg.value; } function withdraw(uint amount) public { if (credit[...
0
votes
0answers
35 views

blockchain solidity tracking system

I am trying to make a code in solidity to add items to a blockchain which contains items and their tracking history (like when trace your order online for an item) (which at first are located in "...
1
vote
0answers
33 views

Blockchain Performance Metrics

How can I measure blockchain execution time, latency and throughput? Which API do I use to measure? Anyone suggest any article or book for me to read about the blockchain performance metrics?
-2
votes
1answer
28 views

Contract is failing on approve function in Ethereum with Solidity [closed]

My contract file is this http://prntscr.com/pvvkme. My Test file are these http://prntscr.com/pvvkme & http://prntscr.com/pvvlmg My migration file is this http://prntscr.com/pvvm5b My errors are ...
1
vote
1answer
67 views

error in remix IDE

I am facing this type of Error in 'remix IDE' while connecting it to 'web3.js@0.20.2' Error: Failed to decode output: Error: insufficient data for uint256 type (arg="", coderType="uint256", value="...
0
votes
3answers
72 views

web3.eth.contract not working

I have web3@0.20.2 installed using npm . when I call web3.eth.contract() it says that it is not a function and when I use new web3.eth.contract it says it is neither a constructor. This is my code &...
1
vote
0answers
17 views

IPFS file uploading issue [closed]

I just installed IPFS version 0.4.22 on my Mac. When I try to upload/add a file in TERMINAL - using the following command: ipfs add myLogo.jpg I get this error: Error: ipfs repo needs migration ...
0
votes
1answer
18 views

How to substitute attributes instead of roles in access control coding for solidity?

Say, the role-based access control consists of two roles. But if I want to replace the roles to maybe location and time, how to go about it?
0
votes
1answer
33 views

Does Geth provide a private or public network?

I'm new to the Blockchain world, lacking experience and I'm looking for some assistance. I'm just syncing with ethereum network by using Geth and rinkeby network. by using this command: geth --...
1
vote
1answer
40 views

Ethereum development environment for Windows 10

I am new to Ethereum and Solidity. Currently learning it from youtube videos and some blogs. So far I have been doing stuff in the remix IDE on a browser. Now I want to perform the same things on my ...
0
votes
1answer
35 views

How to write smart contract to check deployed owner is intitiating the contract or not, everytime?

I want to write a smart contract where it would check it is owner of the deployed contract is trying to instantiate the contract or not. And by doing to i want to allow only the owner to call smart ...
0
votes
1answer
32 views

How often Geth/Parity access the archive chain files? Can I store remote?

I'm running a full archive node to receive and send funds (ETH & other tokens also). The size of the blockchain is very large, so I'm thinking about storing it remotely and mount as an sshfs ...
0
votes
1answer
57 views

Consortium vs. Permissioned Blockchains

I hear these two terms interchangeably Consortium Blockchain and Permissioned Blockchain. Are they the same? If not, can you please show the difference between them. P.S. Since there exists no ...

1 2 3 4 5 34