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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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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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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1answer
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How to upgrade this Crowdsale contract (from DappUniverse)

i'm trying to compile this code (from DappUniversity: https://github.com/dappuniversity/ico_irl/blob/master/contracts/DappTokenCrowdsale.sol) but with the new version of OpenZeppelin, that's use at ...
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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 ...
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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2answers
143 views

Metamask injects one account in web3, but calls contracts using another account

Building a React app, MetaMask injects web3, I get accounts[0] from getAccounts(), then pass it to my contract functions together with other parameters. I want my modifiers to lock incoming function ...
2
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1answer
47 views

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
120 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
98 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?...
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2answers
281 views

Reset all values in a mapping

I am trying to figure out how to have the balance of all players reset to (amount) when a certain condition happens. This is the function that will update a specific player balance. How do I make it ...
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0answers
78 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
47 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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76 views

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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74 views

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
31 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
27 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
27 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
65 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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30 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
173 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
39 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 ...
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55 views

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 ...
2
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45 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
33 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
238 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 "../../...
2
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0answers
107 views

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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0answers
27 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
291 views

Remix: Gas required exceeds allowance or always failing transaction

I have a contract which has transferFrom function mapping(address => uint) balances; mapping(address => mapping(address => uint)) allowed; mapping (address => bool) public ...
2
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1answer
199 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 ...
2
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0answers
65 views

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
35 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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100 views

Can I call a library function from a payable function?

I seem to get a revert each time I try this. I'm unable to get any useful revert message from truffle, so any assistance there might also help solve this. I have a library: library LibInterface { ....
2
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1answer
61 views

Transaction execution and interacting with truffle

pragma solidity ^0.4.23; contract Hotelbooking{ address receiver; function deposit(uint256 _amount) payable public { require(msg.value == _amount); // nothing else to do! ...
2
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2answers
132 views

Truffle interaction with my smart contract getting Vm exception

pragma solidity ^0.4.23; contract Hotelbooking { event Transfer( address indexed _from, address indexed _to, uint256 _value ); mapping(address => uint256) public ...
2
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0answers
81 views

STOP after RETURN in bytecode generated by solidity

I am currently analyzing the code generated by the solidity compiler. Let's take this simple example: pragma solidity^0.4.24; contract test { constructor() public { } } The code generated with ...
2
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1answer
120 views

Transmit array as first parameter in web3.js

When I develop in solidity combined with web3.js, I face some problem recently. I create a contract code below //setContractDetail(index,bool isConsentItem,uint8[] detailItems) function ...
2
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1answer
252 views

Geth Sync Problems | Rinkeby, Ropsten | Deploy contracts

Get Geth to sync --> Rinkeby test network. For the love of god I just want to deploy a contract. I have deployed it to Ganache-cli, GUI, remixIDE, deployed with truffle/Infuria.io...I keep failing to ...
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40 views

What is the command PUSH29 010..00 in solidity compiled bytecode?

If you take a look to the bytecode of several contracts compiled from solidity you can notice that in the first ".data" basic block there is this command: PUSH29 ...
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Interacting with a complex deployed contract from my other contract

For example, I want to call a create market function from augur in my contract. I'm using the recommended pattern, but there are additional contracts that this function brings in, ex ICash, IMarket ...
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449 views

Contract too large

I am sure this has already been answered but I could not find a clear answer. I get the following error: Contract creation initialization returns data with length of more than 24576 bytes. The ...
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0answers
44 views

How does createProxyImpl work in ProxyFactory Contract?

function createProxyImpl(address _target, bytes _data) internal returns (address proxyContract) { assembly { let contractCode := mload(0x40) // Find empty storage location using "...
2
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1answer
25 views

Contract - Demo - Identifier - Only 3 Lines for my contract to work - ¿does somebody know how to fix this?

pragma solidity ^0.4.23; contract Owned { address owner; function owned() public { owner = msg.sender; } modifier onlyOwner { require(msg.sender == owner); ...
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2answers
306 views

Error when running Truffle Test in Terminal

I am trying to use truffle to test my smart contracts and have written some test files. I am getting an error on the terminal trying to run the test and am unsure what the reason is. I access my ...
2
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1answer
297 views

How can we compile multiple smart contracts by compile.js file?

My compile.js file is below const path = require('path'); const fs = require('fs'); const solc = require('solc'); const ballotPath = path.resolve(__dirname, 'contracts', 'blocktitans_ballot.sol'); ...
2
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1answer
238 views

call other contract's external function , the error: The contract code couldn't be stored, please check your gas amount

when I deploy a contract, the truffle frame told me this error :“The contract code couldn't be stored, please check your gas amount”。 the solidity code is: 1) Base.sol pragma solidity ^0.4.22; ...
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0answers
27 views

msg.sender is not showing corect value

I am facing a strange issue. Please read the below case craefully and assit me to geth this issue resolved. I have ERC20Token created by Zeppling templates. [Please ignore syntaxes, I am just trying ...

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