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 make API calls from a .NET Application to an Ethereum Private Network

I'm starting on blockchain development and I have a question: I was wondering if it is possible to make RPC calls to a private ethereum network (handling user private keys is not a problem in our ...
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How can I show on web3j a list of all the instructors added on my blockchain?

I need to show on an html a list of all the instructors that are set up on the list pragma solidity ^0.4.18; contract Owned { address owner; function Owned() public { owner = msg.sender; } ...
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132 views

Unable to send ether to account

I am trying to send ehter using this code web3.eth.accounts.wallet.add(privateKey); web3.eth.sendTransaction({ to:someAddress, from:onwer, value:amount*1, ...
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289 views

Posting data from raspberry pi on blockchain and retrieving it back

I am new to blockchain technology. I just want to know if it is possible to post the data from raspberry pi on blockchain (ethereum) and retrieve the posted data for viewing. My question is if its ...
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signing a transaction on web3js with private key and broadcasting to nodes

I am having an issue with ethereum based project. I made web3 API to communicate to the blockchain. I did this two ways. both call the same function on same address: METHOD 1 (Using Unlocked ...
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Resource allocation and smart contracts

I'm wondering if the following scenario could work with smart contracts. I'm very new to Blockchain so what I'm saying might sound too silly. I have 10 users who are sharing a common resource. There ...
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346 views

How ERC20 Token balance are recovered during Ethereum chain rolling-back

My Answer: Ok, the problem is really with Ganache ... If I use geth, everything is alright. ... ... sorry for your time ... ---------------- The Original Question -------------------- My ...
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has anyone written a nodejs server side component to listen only for Ethereum Events?

I tried the below code to run it using the pm2 module, as nohup command as well. But, this doesn't seem to work. I saw this, but no code is present. so this is what I'm trying to accomplish. I want ...
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2answers
40 views

How can you tell if a mined transaction made permanent changes?

I have set up a private ethereum blockchain and I have defined a new coin. When I send coins from one account to another through the smart contract the transaction is always mined even when the coins ...
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2answers
47 views

Integrate more then one user with one ethereum account

I have many users inside the organization and I want to use same ethereum account for all the users , but with different usernames, so it there anyway to do that ?
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How to automate blockchain transactions of users without having to ask them to enter wallet addresses?

I am working on a game with an in-game currency. The goal would be that when a player buys something, he only have to click on buy, without having to enter the public address and so on. Are smart ...
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371 views

How many tokens are transfered actually when we are using decimals

I have a code below and when I am transferring 1,695,000,000 to a particular address, so actually 0.000000001695 are being transferred. Why is it so? Does that mean to transfer 1.695 billion tokens I ...
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151 views

How can I insert values from web browser Firefox or chrome like html and js to ethereum blockchain?

How to save values from an HTML form into block chain through a browser, I have gone through different tutorials, but it is confusing, how this go-ethereum blockchain and smart contract can access ...
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250 views

Multiple addresses initialization in constructor function

Usually we have one address initialization in constructor function. And that address becomes owner of the contract. While studying erc721 token and going through several examples online i found ceo ...
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240 views

web3 (then property) in ethereum node

Would you please help: When I run the below command in my nodejs console I get the below error: (I am using web3 0.20.0) on Windows 10 web3.eth.getAccounts().then(list => {accts = list}) ...
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Testing Smart Contract

We all know a smart contract is a normal piece of code which can have intended and unintended bugs. DAO attack is such an example where a bug has led to a heavy loss. Suppose I want to check what all ...
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1answer
299 views

What is a standard implementation of upgradable ethereum Token contract

I've readed some code of ethereum Token contracts, such as this one In this code, it does 2 things for upgradable: a contract interface or something like a "abstract contract" called "UpgradeAgent" ...
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1answer
121 views

How my Cryptocurrency Exchange supports Fiat Currency?

Which mechanism is used in Cryptocurrency for converting Fiat currency into Cryptocurrency? Do they maintain stock for particular Cryptocurrency? or they have tie-ups with organisations like (ethereum....
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495 views

Deploying Solidity Contract Using Web GUI and web3

Any guide or step by step Tutorial for deploying a solidity smart using a GUI and accessing the meta mask account ? Please Help
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2answers
384 views

Deploying a smart contract using DApp

I am new to the development of DApps on ethereum blockchain. I want to make a contract Management System in which users can generate their own tokens and crowdsale using my web application. I am able ...
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1answer
313 views

how to connect to a private ethereum testnet with blockcypher

our project uses blockcypher to create eth wallet which can transfer eth now.Blockcypher supports ETH main network and its own testnet. Is there any way to connect the blockcypher node to a custom ...
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1answer
1k views

I sent PRL token to contract address instead of wallet address

I am wondering if i can recover the tokens. I sent PRL tokens to contract address 0x1844b21593262668B7248d0f57a220CaaBA46ab9 instead of myetherwallet address from kucoin exchange wallet. :-( Are ...
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1answer
46 views

Are state changes reversed if the contract “crashes” during execution?

Are state changes reversed if the contract "crashes" during execution? I know that state changes are reversed, if the contract runs out of gas during execution. However, are state changes also ...
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1answer
45 views

Restricting payment from one account only

I am a beginner in ethereum DApp development and I am testing my Contracts in Remix IDE. My question is that can I restrict only one account to pay for all the transactions happening on my application ...
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2answers
59 views

Who are the miners?

In blockchain there are some miners who calculate hash and get reward but my question is who are the miners or how can I be a miner (assume). If there are then I can be connected to a miner? I am ...
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how to get the hash address of previous block while adding a block into blockchain?

In blockchain every block is having three things, Hash address of the previous block Hash of the all the transactions those are part of the current block Nonce, a random value which can be got ...
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1answer
57 views

The value of my variable change

I have two contracts (A and B) in the same smart contract. When I access from B to a A's variable the value is different that I can see from A. For instance, when I access from A to that variable ...
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1answer
260 views

Where does geth store data except for the AppData\Roaming\Ethereum folder?

The AppData\Roaming\Ethereum folder on my computer weighs 5GB, but geth has reduced my disk space by a lot more than 5GB. Where else does it store data?
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1answer
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Can I access last mined block if my node is not there yet?

This might be a stupid question, but I'll ask anyway... I'm currently connected to Ropsten and when I execute eth.blockNumber it says 1853682 (I'm like 300000 blocks away from current last mined ...
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2answers
394 views

how does digital signature functionality in blockchain fulfil the requirement of user identification?

As we are aware that blockchain is a decentralized application and it is tough to implement user identity mechansim in decentralized application so we use digital signature to verify the identity of a ...
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2answers
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Is Merkle tree applicable at block level also?

As per my understanding, Merkle tree is applied in case of transactions. Through Merkle tree we generate root hash transaction from all the transaction present in a block. So does it work the same way ...
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1answer
97 views

testing the hello world application on a different computer when the compute crashes/node not working

I am new to the blockchain technology. I want to test the blockchain functionality of a decentralized ledger. I have created a hello world smart contract(on solidity, geth, mist browser) on computer ...
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3answers
256 views

Unlocking Ethereum wallet using Geth JSON-RPC

When I use ETH with JSON-RPC I have error "message": "authentication needed: password or unlock» and If I manually unlock I have other error "message": "insufficient funds for gas * price + value" Any ...
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Why the maximum number of transactions in a block is 221?

I made a private network with only one node in it, then I sent 2000 transactions like so: var amount = 1; var sender = personal.listAccounts[0] var receiver = personal.listAccounts[0] for (i = 0; i ...
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1answer
104 views

Problems funding Ethereum Wallet

Tried making three separate transactions from two separate wallets (Coinme and Coinbase) each in relatively small amounts (less than $50) to fund my Ethereum Wallet 8.0 for Mac. None have appeared ...
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1answer
790 views

Ethereum Pending Transaction

I am trying to send 2 transactions. eth.sendTransaction({from: eth.accounts[0], to: eth.accounts[1], value: web3.toWei(5, "ether")}) eth.sendTransaction({from: eth.accounts[0], to: eth....
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1answer
239 views

Ethereum mist wallet not synchronising, not showing Ethereum and folder

I am a beginner at setting this up and I used a youtube tutorial to download Mist. The problem is it's not syncing the blockchains. I've tried to debug this by going to users/appdata and inside the ...
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1answer
1k views

Can't compile contract - pragma error and Cannot read property 'interface' of undefined

I am trying to compile this simple contract: pragma solidity ^0.4.18; contract Tasks { struct TaskOwner { address TaskOwnerAddress; bytes32 TaskOwnerName; } mapping (address ...
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1answer
32 views

Smart contract to strore and retrieve address and ID in blockchian using mapping

I want to store some address and their ids in blockchain using mapping and i want to know how to get the stored addresses when searching with their respective IDs.
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1answer
324 views

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
62 views

Interacting with Ethereum smart contract that has been deployed via address

I'am total beginner in Ethereum so how to interact with smart contract via address ? here is the address : 0x259a065256212183490b3ee3f4702c900c37d712 ABI: [{"constant":true,"inputs":[],"name":"...
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1answer
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How to store blockchain data in database

I am new in blockchain. I want to know that which database should I use to store blockchain data? How can i store blockchain data in codeigniter?
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1answer
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I got this problem in my private ethereum blockchain(Node is not syncing, Node data write error ,Synchronisation failed, retrying)

I am new to ethereum and right now getting the ethereum blockchain using geth with geth --port 3000 --networkid 58342 --rpc --rpcport 8545 --rpcaddr 10.0.0.2 --rpccorsdomain "*" console INFO [03-...