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1500 questions
133
votes
6 answers
What is a DApp?
There are new terms in Ethereum like smart contract. What is a DApp and how is it different from smart contracts?
eth
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126
votes
3 answers
Which cryptographic hash function does Ethereum use?
Many sources refer to the use of the "SHA3" cryptographic hash function within Ethereum, but the Ethereum project began before the SHA3 standard was finalised, and there was some confusion/controversy around the final parameters selected for the…
Jeff Coleman
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118
votes
11 answers
How would I explain Ethereum to a non-technical friend?
I've recently attempted to explain Ethereum to several non-techy friends.
My explanation usually involves starting with a comparison to Bitcoin, but this quickly becomes complicated as I then have to explain the backstory of how the Bitcoin…
Richard Horrocks
- 37,835
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117
votes
6 answers
Difference between CALL, CALLCODE and DELEGATECALL
CALL and CALLCODE take the same number of operands (in the execution stack). For the exception flag being pushed on top of the stack: 0 means exception, 1 means successful execution. CALL is easy to understand, but I could not digest the subtle…
Loi.Luu
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116
votes
2 answers
What does the indexed keyword do?
What does the "indexed" keyword do in the below line of code? I'm guessing it just tells the event object that the following input should be logged? Can we use it other places ie outside of events?
event Transfer(address indexed from, address…
jyapx
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115
votes
8 answers
Ethereum block architecture
Where can I find a description (preferably a diagram like below) showing the block structure in an Ethereum blockchain?
Credits: Wikipedia
zanzu
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112
votes
6 answers
What is the difference between Swarm and IPFS?
IPFS seems a little slow on existing dapps. will Swarm load content more quickly? Also- is there a roadmap for swarm?
bamos
- 1,944
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111
votes
4 answers
What is Geth's "fast" sync, and why is it faster?
One of the answers to this question suggested using Geth's --fast flag to help quickly synchronise the block data.
How does the flag work, and how does using it speed up the synchronisation? Are we syncing less data, or are we in some way performing…
Richard Horrocks
- 37,835
- 13
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- 144
108
votes
7 answers
How can an Ethereum contract get data from a website?
What is the process/workflow behind the process where an Ethereum contract gets some data from a website?
Dawny33
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108
votes
2 answers
What's the difference between 'msg.sender' and 'tx.origin'?
If either are used in the body of a Solidity function that may change the state of a contract (write call), what's the primary difference and/or benefit of using one over the other. For example:
function setOwner() {
owner = msg.sender;
…
dbryson
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104
votes
5 answers
Difference between require and assert and the difference between revert and throw
I was looking at the docs and I'm looking for clarification on the difference between require and assert and throw and revert.
assert(bool condition): abort execution and revert state changes if
condition is false (use for internal…
Daniel Kobe
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101
votes
3 answers
What is an uncle/ommer block?
The Ethereum blockchain is described as containing "ommer" blocks, usually called "uncle" blocks by the general public. What is an ommer/uncle block, and why are they needed?
Jeff Coleman
- 22,059
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96
votes
12 answers
Common useful JavaScript snippets for geth
In Geth you can loadscript any javascript file.
I discovered this one on the wiki which I like a lot:
function checkAllBalances() {
var i =0;
eth.accounts.forEach( function(e){
console.log(" eth.accounts["+i+"]: " + e + " \tbalance: " +…
euri10
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95
votes
7 answers
How to concatenate strings in solidity?
I'm trying to concatenate two strings in solidity.
I tried with + or . but neither option works. There is not much documentation on string concatenation yet. Is it even possible?
If not, can I insert variables into strings?
q9f
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91
votes
9 answers
Can contracts pay the gas instead of the message sender?
Is it possible for a contract to pay the gas costs (or part of it) that result from the contract being called? Or does the sender of a message always pay the resulting gas costs no matter what?
mKoeppelmann
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