Questions tagged [solidity]

Solidity is a contract-oriented, high-level language whose syntax is similar to that of JavaScript and it is designed for writing smart contracts in Ethereum to run on the EVM. Solidity is statically typed, supports inheritance, libraries and complex user-defined types among other features.

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Difference between “decoded input” and “input” in Remix?

What is the difference between "decoded input" and "input" in the remix output? If these functions were to be called in an actual blockchain, would the "decoded input" be saved in a block, and thus ...
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In solc 0.4.x assembly, how can I check if a non-constant function returns 'bool' or nothing?

I know how to do it for a constant function, for example: pragma solidity 0.4.25; contract Callee0 {function func() external pure returns (bool) {return false;}} contract Callee1 {function func() ...
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Web3 Ethereum log subscriptions - removed field?

I am trying to subscribe to Ethereum events (via Infura) but I'm a bit confused. I am following this documentation: https://web3js.readthedocs.io/en/v1.2.0/web3-eth-subscribe.html#subscribe-logs ...
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1answer
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Modifying simple function with inline assembly

I'm trying to write a super simple contract that's gas efficient utilizing inline assembly in solidity. All this function needs to do is create a child smart contract with one function, self destruct....
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Performing a C-like pointer increment in Solidity

I have a memory or calldata struct with an attribute of type byte[]. I want to have a memory variable with that data, except for the first n Bytes. In C, you'd just write typename variablename = ...
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Is there any particular reason the position of the public/private keywords change depending on whether it's a function or variable?

I fear it will be difficult for me to remember if this quirk of the language is arbitrary...
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Ethereum Smart Contracts/dApp’s open source license?

Can a smart contract in which it’s source was released be GPLv3/GNU licensed? I.e. if a company were to release the source code to a smart contract, can that smart contracts source code be GPLv3/GNU ...
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Combine two addresses into one

I want Solidity code to define a function f that would map two Ethereum addresses A, B into a new address X = f(A,B) such that there is nearly zero probability that X is an already taken address (an ...
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How Can You Map a Struct Twice With Different Keys?

I have a struct mapped with an address as the key. I want to iterate through all values of that mapping with another key value, in this case a nonce that I generate in the contract. Is this possible? ...
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Increasing the difficulty/cost of manipulating an on-chain PRNG?

well, from what I understand since everything on-chain is deterministic so theoretically there's no way of having a real cryptograhically secure random number generator that cannot be manipulated by ...
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Name Styling Best Practices Internal/External variables/functions etc

The solidity docs clearly specify how to style function order, types etc. However, are there an appropriate way to also separate between internal/external variables, functions etc. I see some people ...
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0answers
38 views

Nested usage of interfaces?

Using solidity ^4.x, it seems I can use an interface as a parameter type in a function from a different interface. Example: interface IERC20 { function transfer() external; } import "./IERC20....
2
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1answer
125 views

Using 'call' from a constant function

I am trying to determine the behavior of call when executed from a constant function. Of course, the compiler issues a warning on that: Warning: Function declared as view, but this expression (...
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Oraclize ethereum bridge : Notifying __callback tx error to frontend

I have called API dynamically using Oraclize with the delay of 10 minutes. The code is shown below and it works well. uint256 constant DELAY = 60*10; event Log(string result); function ...
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2answers
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To transfer tokens from owner address to an address, if latter address moves some other tokens to a given particular address

I am writing a contract for an ERC20 token (say ABC). Is it possible to airdrop some of these newly minted ABC tokens to those ERC20 addresses, every time, if they transfer a different token (named ...
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How the following pairing equality be verified in Etherum Smart contracts?

I have found available precompiled contracts in solidity. For example, this answer enter link description here points out a precompiled contract that can verify BLS signature. However, looking to the ...
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1answer
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Use uint40 for time in Solidity?

My question is: Should I use uint40 for time in Solidity? All the examples I've seen use uint256 for time, however, I think it's too wasteful -- while using uint32 is maybe a little aggressive due to ...
2
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1answer
36 views

Ethereum linking library with contract not working as accepted…returning any state variable returns just the default value

my library pragma solidity ^0.5.8; library SafeMath { function add(uint256 a,uint256 b) public pure returns (uint256) { return a+b; } } My contract pragma solidity ^0.5.8; import ...
2
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1answer
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bn256 and Boneh-Boyen digital signature in solidity

I am looking to have a full-fledged implementation of bn256 in solidity. And Boneh-Boyen digital signature. Is there is any available built-in libraries or implementation in solidity to bn256 and ...
2
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1answer
168 views

Unable to deploy the smart contract using solc compiler in mac

I am trying to deploy the Lottery contract using solc compiler of verison 0.4.17 but it's showing me nothing. But the same contract is working good in the remix ide. I providing you the the Solidiy ...
2
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1answer
301 views

openzeppelin,VM Exception while processing transaction: revert

using openzeppelin-solidity to create crowdsale. Then I use this statement to Buy Token: MyCrowdsaleInstance.sendTransaction({ from: purchaser[1], value: web3.utils.toWei("0.5", "ether"), ...
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2answers
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Hashnot matching generated from solidity contract and web3js

I want to make hash same as generating by solidity contract from web3 or ether's js. In solidity contract hash generation by below : sha256(abi.encodePacked(no of parameters)). Kindly help for it. ...
2
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2answers
138 views

Best way to create identity contracts for organisations

What is the best way to create identity contracts for organisations based on their information like name, address, organisation type(buyer/seller) etc. I have tried using factory pattern to create ...
2
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2answers
164 views

How could Compound's interest accruing every block? How's that implemented?

Here I'm referring to https://compound.finance, which is quite an awesome product. One thing inspires me most is that the interests accrued in Compound are updated per block. How's that even possible?...
2
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1answer
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Problem on returning fields of a struct inside a mapping

I have the above code mapping(string => Owner) public Owners; function addOwner( string memory name, string memory surname, string memory fathername, string memory mothername, string memory ...
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0answers
95 views

What happens when some files use the ABIEncoderV2 and some don't

The version 2 of the ABIEncoder used by solidity can be enabled with: pragma experimental ABIEncoderV2; What happens if I compile with truffe a project that has some files with that pragma and some ...
2
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1answer
71 views

How to return values from dynamic array push function?

How to fetch value from dynamic array push function? Below is the code of pushing function, but how will I fetching that array values? contract PushStruct { struct MyStruct { uint field1; ...
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Solidity get return variable from a send method in React

I'm trying to call a method that pushes data to my Blockchain and then returns back the ID of the new struct I created. This is how I'm calling the method in my React code: const documentId = await ...
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Why truffle deploy fail with address value=0 after I upgrade to version 5.0.5?

I have a truffle 2_deploy_contracts.js something like this : const sample = artifacts.require('./Sample.sol'); module.exports = function(deployer) { deployer .then(()=>deployer.deploy(...
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Why I can't use two functions with same name, but different parameters

I have a function which returns address but it gives me error if I try to read it. I'll explain by a quick example: Solidity: contract TestOneReturn { mapping(uint => uint) m_Data; ...
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Function call always returns 0

Working with a simple contract to get the hang of this. I can't seem to get the correct value back from my contract function. It always outputs 0. Truffle version: 4.1.15 Contract: pragma solidity ...
2
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1answer
39 views

How to implemet condition for constructor?

Looking to learn solidity so need your support for this I have made a constructor in my contract where maxAvailableNumber = 1; What I want to do is if the balance of user is more than certail limit ...
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0answers
33 views

Can I import a Library from a Library?

Is it possible to import a library into another library? I give a simplified example below of what I'd like to achieve: library structLib { struct Point { uint X; uint Y; } } ...
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0answers
30 views

How to change prefix of signature in Javascript?

Is it possible to change the signature prefix, which by default: "\x19Ethereum Signed Message:\n32" Can I change it to another prefix? I need to get a signature in solidity in this way: bytes32 ...
2
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1answer
78 views

Trying to understand why my test.js fails

I have a function that is not passing my tests in JS but the function works as expected in Remix. Can you help me contract.sol function test1 () public view returns(bool){ return(true); } ...
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33 views

How does the Solidity compiler translate the `using .. for` statement?

I'm trying to figure out how using [Library] for [type] is compiled by the solc compiler. I noticed that address placeholders are not in the bytecode as with other library references. So what ...
2
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1answer
202 views

Call a payable contract's function from another contract via an interface

I have two contracts, they are connected via an interface. When user calls contract1 function, it uses an interface to call contract2 function which updates it's storage. My problem is that I can ...
2
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1answer
49 views

How to get the return type of a function of an already deployed contract?

I am currently working on a real estate blockchain project. Now I have 2 contracts user.sol and property.sol. The person who is registered on the website through user.sol can only buy or sell property ...
2
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1answer
103 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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0answers
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Can I send transaction to a view|pure function?

This is the contract: uint public result; address public owner; constructor() public { owner = msg.sender; } function add(uint a, uint b) public returns(uint) { result = a + b; return ...
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0answers
103 views

Unable to call setter function in solidity using Infura

Solidity code contract Greeter { string public greeting; function Greeter() public { greeting = 'Hello'; } function setGreeting(string _greeting) public { greeting = _greeting; } function ...
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49 views

How to add function buy to buy button that need array index

I am new to this smart contract and blockchain. I'm trying to do simple selling goods dapps. But i'm stuck at the buy button. I have array for the products. constructor() public { goods[0].owner =...
2
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1answer
40 views

mapping data is not returned from SmartContract during the first time add operation

I have the below given SmartContract and the test. Please note that, when i try to execute the test, only after the second call to the grantAccess method, I am able to get the mapped value. pragma ...
2
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1answer
322 views

Passing one contract instance as an argument to the constructor of another contract

I need to use the functions of the ERC20 contract in another contract. The ERC20 contract is from the openZeppelin contract library. I found the following code on a website: import "../../...
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Using OpenZeppelin's increaseTime.js

I'm writing a test for a time-dependent solidity function. I'd like to use the increaseTime.js helper from v1.12.0 of OpenZeppelin's library. When I try to call this helper inside my test, I get an ...
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web3 - get all contract public variables?

I have an abstract worker contract and few that inherit from it. Those contracts have some public variables, each one different. I want to display them on my website. Is there any way to return all ...
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30 views

One time catastrophic solidity bug suddenly vanished

I'm writing a Blackjack game in solidity. In the following function, the player ended up winning one time with a hand strength of 30 after doubling down even though they should have busted. ...
2
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1answer
261 views

How to implement percentage deposit function to smart contract

I need to implement on the deposit function when the ownerAddress is doing a deposit a 10% to be freeze in the smart contract and and if the ownerAddress want's to call the returnDeposit function by ...
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0answers
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Why is putting data to storage more expensive during the deployment of contract than storing the same data by a method?

I am working with truffle and solidity (v0.4.23) and found out that when I pass in an argument of constructor some bigger amount of data (16kB) that are saved to storage of a smart contract, it is ...
2
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1answer
44 views

Why use different gas?

I have this contract with this functions, why each use different gas amount? pragma solidity 0.4.24; contract Foo { //transaction cost: 21471 gas //execution cost: 199 gas //total cost: 21670 ...

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