Linked Questions

68
votes
2answers
27k views

Solidity: What is the difference between `view` and `constant`?

Solidity 0.4.16 introduced the view and constant function modifiers. The documentation says: constant for functions: Same as view. Does this mean view is just an alias for constant? If so, why do ...
27
votes
3answers
29k views

How to get return values when function with argument is called?

I am writing below a simple contract which stores all results of questionnaires for each ID. contract answer{ mapping(address => mapping(string => bool)) voters; struct qList { uint ...
11
votes
2answers
5k views

View/Pure Gas usage - Cost gas if called internally by another function?

I know similar questions have been asked before however I could not find an good explanation for the following, In one of the tutorial it says: Pure and View functions don't cost any gas to call ...
9
votes
3answers
5k views

Who pays gas for smart contracts?

I'm currently writing my first smart contract and I'm trying to figure out how to inject gas into the contract, of course, if it's possible. I'm not sure If I got it correctly. With every transaction ...
5
votes
2answers
3k views

Solidity Invalid implicit conversion from string memory to bytes memory requested

pragma solidity ^0.5 contract ProofOfExistence { // ... some code here function proofFor(string memory document) public view returns(bytes32) { return sha256(document); } //...
1
vote
2answers
324 views

Contract returns default value

I'm trying to create a contract which calls boolean method on another contract. However, for some reason it doesn't work. Here is an example: pragma solidity ^0.4.23; contract Season { address[...
0
votes
2answers
70 views

Making contract compatible with newer solidity compiler

I have a simple timelock contract however it doesn't work with modern solidity compilers, Could anyone make my contract compatible with solidity newer than 0.5.16? Thanks. Here is the code, it only ...
0
votes
1answer
31 views

return array is not showing pushed value

This must be silly question but as a new learner i am trying to understand array in solidity and run this code in remix, compiled and deployed the contract on ropsten platform. I want to see the array ...
0
votes
1answer
31 views

Why this function doesnt need Gas for execution?

pragma solidity ^0.4.17; contract Lottery{ address public manager; address[] public players; function Lottery() public { manager = msg.sender; } function enter() ...
1
vote
1answer
25 views

Function which only reads data still using gas/tx fee

I have a function call which only reads data from contract but it still costs gas to execute: function foo(int256 x) public returns (bool) { if(tuna[x].validOnce == true){ if(dog[x] == ...