Questions tagged [solidity-0.5.x]

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. Solidity version 0.5.0 is a specific version that includes a number of changes to the language and introduce new features.

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Is the primary reason keccak256(a, b, c) was changed to keccak256(abi.encodePacked(a, b, c)) because of the forgery attack vector?

I am/have been a noob developer attempting to develop dApp. When keccak256(a, b, c) was suddenly deprecated years ago, it seemed to me like it just added unnecessary complexity. In hindsight, I have ...
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Why is array.length giving "length" not found or not visible after argument-dependent lookup in mapping?

Here's how I defined an array of my struct: struct FoodItem { string name; uint price; bool available; } mapping(uint => FoodItem) public foods; Now I want to delete an ...
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47 views

How to tell how much money executing something will cost

I understand the difference between transaction costs and execution costs, but I don't understand two things: What does the "gas" readout in Remix refer to? How do I create an estimate of ...
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Include library function without function body

Using solc 0.5.0 it's possible to compile a contract that has a library function implemented with no body. For example: library Hasher { function MiMCSponge(uint256 in_xL, uint256 in_xR) external ...
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Error HH411: The library openzeppelin-solidity is not installed. Try installing it using npm (for old 0.5.0 solidity code)

I have solidity project with files like pragma solidity ^0.5.0; import "openzeppelin-solidity/contracts/ownership/Ownable.sol"; When I try to compile, I get error on not installed library ...
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24 views

Compiler version not recognized

Anyone have any ideas how to fix this? Compiler version is there. $ solc --optimize --abi ./contracts/MySmartContract.sol -o build ./contracts/MySmartContract.sol:1:1: Warning: Source file does not ...
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90 views

What is the logic by which tokens are ordered when creating a new Uniswap V2 pair?

When creating a new pair contract via the UniswapV2Factory contract, the order in which tokens get assigned in storage (that is, the token0 and token1 vars) cannot be arbitrarily set by the caller: (...
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Ethereum DApp with user authentication

I'm creating a healthcare DApp and how can I create user authentication ( For Doctor and Patient). I'm using JavaScript and HTML for most of my UI.
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I can't compile my solidity contract, can someone help correct the code. i've been trying for about 24 hours now

This is my smart contract: pragma solidity ^0.5.0; contract Agent { struct patient { string name; string dob; address[] doctorAccessList; uint[] diagnosis; ...
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OpenZepplin contracts, is it good to go back to old contracts for solc 0.5

I am trying to use an existing contract which only works with pragma 0.5. I also use openZepplin contracts and I want to know if it is okey to go back to the old openZepplin contract that utilizes the ...
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28 views

call method in compiler 0.8

how can i change this for older compiler versions like 0.4.24? (bool success, ) = transaction.to.call{value: transaction.value}(transaction.data); and if you have time please explain to me the call ...
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Storing constants in Storage vs Creating a view function? (Solidity 0.5.17)

So, which would be gas efficient? Reading a storage variable in a state-changing function? OR Reading from a pure function in a state-changing function? Example: contract Test { uint256 public a = ...
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I need to understand a line of code inside a contract => startTime: _startTime == 0 ? currentTime() : _startTime

I am reading a contract from this location : https://gist.github.com/rstormsf/7cfb0c6b7a835c0c67b4a394b4fd9383 I am not able to understand the logic in the code line 72 startTime: _startTime == 0 ? ...
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15 views

Function overloading problem

As we know, it's possible to distinguish between two functions have same names. Different number of the functions arguments is a way for that. If the number of arguments is the same but the set of the ...
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1answer
39 views

Contract pay the rest of gas fee

This is my payable public method1 : //Do sth if (condition) method2(); and as you know, if method2 is called, the user should pay the gas fee for it as well. How can call method2 from inside the ...
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Truffle test is failling with transferFrom.call

When I run tests with the following code, I get the following error: Error Error: Returned error: VM Exception while processing transaction: revert Tests it('Handles delegated token transfers', () =...
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18 views

How to add data to an array inside a struct?

I have made a struct which contains an array . Now when I am adding data to the struct, I'm not able to add data to the array . struct User { uint256 limit; // spending limit uint256 ...
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92 views

How can a contract accept some ether and send a stablecoin in return

My contract has to take ETH as a collateral and send some stablecoins ( like USDC) to user. How can I use any stablecoin into my contract , assuming contract has an infinite supply of USDC ? I too ...
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40 views

Member "owner" not found or not visible after argument-dependent lookup in type

pragma solidity ^0.5.0; contract reeler{ uint public id; string public name; string public addres; string public state; string public pincode; uint public yarncount = 0; mapping(uint =&...
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61 views

how to get array that contain certain value

I'm new in solidity, I want to ask, in my case I want to store a data that may contain the same user ID but different value inside it each transaction, here is my smart contract: pragma solidity 0.5; ...
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116 views

Transfer ether in solidity 0.5.16 with truffle

I am currently working with Truffle and Ganache, therefore I use Solidity compiler version 0.5.16. With that version I have some problems to send ethers. I want to transfer ether to a specific address....
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How to ensure that a string parameter to a function is not empty?

Lets say that I have a function which needs two string parameter , function data(string memory _firstname, string memory _lastname) public { buyer[msg.sender] = Buyer(_firstname, _lastname); } Now, I ...
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298 views

Gas fee optimization questions [duplicate]

Can some recommend a way to save gas fees? a = a + 1; a++; I heard about this; Pack struct tightly Mine looks like this. I am not sure about size of address, ENUM variables and array without length. ...
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100 views

Validation of integers on solidity

I have this function and require the _price variable to be positive, But when I pass a negative int, it accepts the integer! How can I validate the input? The Contract : function createProduct(string ...
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error when I run truffle test

TypeError: Cannot read property 'call' of undefined at Context. (test/TdetayProofTest.js:18:74) here my test: var TdetayProof = artifacts.require("./TdetayProof.sol"); contract('TdetayProof',...
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What is the purpose of EVM tags, their haphazard arrangement and their relationship to functions?

I want to understand the purpose of tags in EVM assembly and their relationship with Solidity function. pragma solidity ^0.5.1; import './Mod.sol'; contract MOFTest{ ModifiedBank mb; ...
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95 views

How to I initialise an array inside the contructor in solidity?

I'm using the remix IDE.I want to define the size of the array at the time constructor is called. Someone please help. This is what I tried : pragma solidity >=0.7.0 <0.8.0; contract Vote { ...
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372 views

What's wrong with my buyToken function?

Here is my solidity interface IERC20 { function decimals() external view returns (uint8); function totalSupply() external view returns (uint); function balanceOf(address owner) external ...
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124 views

require(msg.sender.call("")): No matching declaration found after argument-dependent lookup

I am trying to compile the following Solidity program: pragma solidity ^0.5.9; contract Mutex { bool locked; modifier noReentrancy() { require(!locked); locked = true; ...
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602 views

Remix: ParserError: Expected pragma. import directive, or contract/library/interface definition

I'm trying to use Remix to interact with a suite of contracts. One of the contracts being used is OpenZeppelin's Ownable contract. I copied from the link above, and pasted it into Remix, with a few ...
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Issuing 1-1 eth for token problem

pragma solidity 0.6.6; // import "./XYZToken.sol"; contract Vault { mapping(address => uint256) balanceOf; mapping(address => bool) hasDepositedEther; mapping(...
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49 views

Transfer funds to inherited smart contracts [closed]

How would I make this work - the balanceOf[Pool, System + Cube] doesn't seem to work ;-; // SPDX-License-Identifier: GPLv2 pragma solidity ^0.7.0; import "./Pool.sol"; import "./Cube....
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303 views

Using inherited constructor in Solidity >=0.5.0

I want to use a contract inherit from another contract and use the parent constructor after using another commands in inherited constructor. So I wrote: pragma solidity ^0.5.10; contract A { ...
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170 views

How to call the super contract function where msg.sender should be same in solidity?

I am trying to call contract A.fun_A() via Contract C contract A{ function fun_A(address tenant, uint itemId){ //Here the msg.sender should be msg.sender in C require(msg.sender == ...
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39 views

Get a blank address

I have a little problem with my code. I'm trying to follow who are the current sender and the previous sender of a transaction respectively with the variable currentSender and lastSender, and then ...
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1answer
68 views

Getter of mapping inside a struct

I wanted to create a getter function to access a mapping nested inside a struct. But the function that I made required me to use the expiremental version (I'm on Remix). So I used the expiremental ...
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1answer
35 views

Else if structure gives the wrong output

I have a little problem with a else if struture that doesn't give out the right result. Here is the code: pragma solidity >=0.5.16; contract SupChain{ enum StateType {A, B, C} ...
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26 views

Negative integer function

I have the following problem, one of my function has a variable where the uint can be negative but I don't know of that before the user enter in the form the integer. How do I settle this problem ? ...
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1answer
1k views

Warning! Error encountered during contract execution [execution reverted]

I have an ERC20 Mintable+Burnable Token created on solidity 6.11 and a sale contract on solidity 5.0 I am getting error when i send ETH to the sale contract. https://rinkeby.etherscan.io/tx/...
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154 views

Flashloan callFunction being called internally

I had a chance to look at this contract. contract Flashloan is DyDxFlashLoan { uint256 public loan; constructor() public payable { (bool success, ) = WETH.call.value(msg.value)("&...
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321 views

Different compiler versions in OpenZepplinn ERC721 folder

We have created a contract by inheriting ERC721Burnable, Ownable contract from openzepplin. The compiler version we are using in our smart contract is 0.6.0. I flattened the smart-contract by using ...
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442 views

How to get require() error message?

I can see the error message on Etherscan. But I can't find it in getTransactionRecept(). Is there any special settings that I need set in my Genesis.json before I can see it?
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158 views

Is it true that we can't make multiple Transfer() to the same address within a single transaction now?

The code below is for illustrative purposes only. Not the actual production code. function payCommission(address[] payee) public payable { for (uint i = 0; i < payee.length; i++) payee[...
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2answers
25 views

Couldn't understand the logic behind code for mulitdeed payout contract

While searching on the web I came across this page the user has created multiple examples of solidity smart contract On multiple payout deed smart contract I can't understand this line duePayouts = ...
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1answer
32 views

Compilation Eror: One contract accessing the variable of another contract

I am trying to compile two contracts. I am getting 'balance' variable error in "HoneyPotCollect.sol" contract. Is balance not a global contract variable? Somebody please guide me how to ...
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427 views

Why solidity doesn't use " Null " and "undefined"?

Like Python or any other language why does Solidity avoid having the Null and undefined properties?
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46 views

Why does Solidity not use the years keyword?

Solidity has keywords like seconds, minutes, hours, days and weeks that are used to specify units of time. Why do they not have years?
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79 views

How to make my contract balance as private in Ethereum?

Suppose there are two contracts, A and B. Obviously, balance of A is public and B can read it with address_of_A.balance. Is there a way to make balance of A as a private data and B can't read it with ...
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1k views

Data location can only be specified for array, struct or mapping types, but "memory" was given

I am new to solidity. I was trying to compile the following code in chrome browser with Remix. I am getting the following error "Data location can only be specified for array, struct or mapping types, ...
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Problem: Payment between smart contracts without reducing the balance of the sender contract

I work on Truffle. I have two smart contracts A and B. Codes of them are same. A should transfer some ether to B and store some information about this payment. I funded A with METAMASK. But, whenever ...