return array is not showing pushed value

Question

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 value which i am returning in the end.But calling that getA function gives nothing. I'm doing the transaction in metamask.

pragma solidity 0.5.1;

contract SolArray{
    uint[] a;

    function getA() constant returns  (uint[] memory){

        a.push(123);
        return a;
    }


}

score 1 · Accepted Answer · answered May 31 '19 at 17:58

I don't see how that would compile because constant is deprecated in 0.5.1.

In any case, remove constant because "read-only" is inappropriate if you want the storage state to change. In case that sounds cryptic, have a look over here: https://blog.b9lab.com/calls-vs-transactions-in-ethereum-smart-contracts-62d6b17d0bc2 and When to use "View" and "Pure" in place of "Constant"

Instead of your array, you'll get a transaction hash and you'll want another function to return the array. You can do that with public.

Try it like this:

pragma solidity 0.5.1;

contract SolArray {

    uint[] public a;

    function pushA(uint value) public {
        a.push(value);
    }
}

You will see that function a() asks for a row/index to return. This is the scalable pattern that will have a consistent gas cost at any scale. A client would iterate the array to get all rows.

To make it more like your original code, you could add a function to return the whole array, with the warning: This is not scalable. It will cease working when the gas cost to return the whole thing exceeds the block gasLimit.

pragma solidity 0.5.1;

contract SolArray {

    uint[] public a;

    function pushA(uint value) public {
        a.push(value);
    }

    function getAll() public view returns(uint[] memory) {
        return a;
    }
}

Hope it helps.

return array is not showing pushed value

1 Answers1