Styjun

So I have this contract and the funder can retrieve the total amounts of a specific campaign through the getFundsByAddress function. The problem is that if a campaign has more than 30 thousand founders,the contract is not able to execute the code because it would need to go through the 30 thousand times so can find all the correct addresses

In the Rinkeby nework the max a loop it can reach is 30k, after that is returning 0

How can I resolve such cases?

contract CrowdFunding 
 struct Funder 
 address addr;
 uint amount;
 

 struct Campaign 
 address beneficiary;
 uint numFunders;
 uint amount;
 mapping (uint => Funder) funders;
 

 uint numCampaigns;
 Campaign[] public campaigns;

 function newCampaign() public returns (uint campaignID) 
 campaignID = campaigns.length++;
 Campaign storage c = campaigns[campaignID];
 c.beneficiary = msg.sender;
 

 function contribute(uint _campaignID, uint _amount) public 
 Campaign storage c = campaigns[_campaignID];
 c.funders[c.numFunders++] = Funder(addr: msg.sender, amount: _amount);
 c.amount += 100;
 

 // not tested
 function getFundsByAddress() public view returns (uint[] memory) 
 Campaign storage c = campaigns[0];
 uint cont = c.numFunders;

 uint[] memory allAmount = new uint[](TotalAmountOfUser);

 uint counter = 0;

 for (uint i=0; i < cont; i++) 
 if (c.funders[counter].addr == msg.sender) 
 allAmount[amountCont] = c.funders[counter].amount;
 
 counter++;
 

 return allAmount;
 

I don't see anything special with the number 30K that would explain this.

Your problem could be that the transaction is either running out of gas or is hitting the block gas limit. If you have to loop through the array and cannot do it in any other way you should consider looping through the array in multiple transactions (i.e. 0-9999,10.000-19.999, ...).

However, looping through so many entries will be quite expensive in terms of gas which on a real network costs money. But if it cannot be done in another way then the above should help you.

It's hard to guess at what getFundsByAddress is supposed to do because the code doesn't compile and the loop doesn't seem to do anything. (The loop variable i is never used.)

But if I had to guess, it's supposed to return the sum of the contributions made by the caller. If that's the case, just keep track of that total as contributions are made and avoid the loop altogether:

mapping(address => uint256) public totalContributions;

function contribute(uint _campaignID, uint _amount) public 
 ...

 // Add this line to keep track of the total.
 totalContributions[msg.sender] += _amount;


// No need for getFundsByAddress at all because a call to `totalContributions(address)`
// (the auto-generated getter) does the trick.

// But if you want a function that returns specifically `msg.sender`'s total:
function getMyContributions() external view returns (uint256) 
 return totalContributions[msg.sender];