Gas for view functions

Question

I read in many places that view functions do not cost gas however that's not true because they cost gas for blockchain operations even if those do not change the state. Correct me if I am wrong For example:

pragma solidity ^0.4.17;

contract myContract {
    uint[] public anArray;   /// assume it has 1,000,000 (1Million) elements

/* function which returns how many times a specific element is in the n array*/

    function elementIndex(uint element) public view returns(uint){
        uint counter;
        for(uint i; i<anArray.length; i++){
            if(anArray[i] == element){
                counter++;
            }
        }
        return counter;
    }
function returnAllElements() public view returns(uint[]){
return anArray;
}}

The real problem comes on the front end when the array has 1 million elements. Running elementIndex() will never work because the iteration will take too long. returnAllElements will not work either (I assume).

What can be done in such circumstances?

score 6 · Answer 1 · answered Sep 25 '18 at 09:17

6

View will not cost gas only if called from outside the network, that is if a function in a contract is view and is called from another contract it will cost gas.

The reason it will not cost gas if called from outside the network is that the function can be resolved in the local node that you are using to connect to the network without submitting a transaction.

Hope this helps.

answered Sep 25 '18 at 09:17

Jaime

8,340
1
12
20

view only costs gas when called from normal (state changing) function, no? I don't think it matters if you call view from other contract as long as the function in other contract is also view. Or i'm wrong? – Maxpeinas Sep 25 '18 at 11:08
@Jaime, @Maxpeinas The answer still does not make sense. Could you clarify it for me? This part the function can be resolved in the local node that you are using. What is a local node? If you running a website in Azure - you most likely do not have an access to the console of the Unix (unless owning a virtual machine) and you are not installing any Ethereum nodes locally. Do you STILL not pay transaction fee in such cases? – Alex Jun 15 '20 at 12:24
I call local node the node to which you are connected, it Infura etc. If you call a view function the node does not have to broadcast a transaction it can get the value just executing the function locally. However, if you are submit a transaction and one of the operations is to execute a view function, it will consume gas. In summary, if the view function is called internally (during the execution of a transaction) it will have a cost. If it is called externally (i.e, a webapp that is reading the value of a variable) it won't have any cost. – Jaime Jun 15 '20 at 17:38

score 4 · Accepted Answer · answered Sep 25 '18 at 02:33

In your case, both elementIndex and returnAllElements functions will cost no gas as both the functions are reading state variables from the blockchain and give an intended result.

You can optimize the above functions to reduce a time taken by them.

Refer the following question to understand View/Pure Gas usage - Cost gas if called internally by another function?

Refer the following blog to understand the difference between calls and transactions in ethereum -

https://blog.b9lab.com/calls-vs-transactions-in-ethereum-smart-contracts-62d6b17d0bc2

Gas for view functions

2 Answers2