I'm using solidity compiler ^0.4.23, I added logs to the function at exception points like this:

function firstSaleDelivery(address _beneficiary, uint256 rate) public onlyOwner{
  require(!presaleOpen && !firstsaleOpen, "First Sale is NOT CLOSE");
  if(preSaleTokens >= 0){
      saleTokens = saleTokens.add(preSaleTokens);
      preSaleTokens = 0;
  uint256 ethers = firstSaleFunds[_beneficiary];
  uint256 tokens = ethers.mul(rate);    // <u>
  require(saleTokens >= tokens, "NO Sale Tokens Available");
  if(ethers >= 5 && ethers <= 9 ){
    tokens.add((tokens.mul(10)).div(100));            // <u>
  else if(ethers >= 10 && ethers <= 200 ){
    tokens.add((tokens.mul(25)).div(100));            // <u>
  saleTokens = saleTokens.sub(tokens);


When I invoke the function, and if I face any exception, I can't see these Logs, where I can see them?

  • you can use remix to debug your code – Badr Bellaj Apr 26 '18 at 11:19
  • I don't want it for debugging purpose, I want my users of contract know why their transaction has failed. – Fariha Abbasi Apr 26 '18 at 11:38
  • so make it a bool function which returns false when it fails!! – Badr Bellaj Apr 26 '18 at 11:40
  • Returning a false doesn't really say anything about why it failed.. – Lauri Peltonen Apr 26 '18 at 11:53
  • Yes, my purpose is to let users know about WHY it failed, – Fariha Abbasi Apr 26 '18 at 11:59

Logs are not produced if the transaction reverts (see this answer: Is it possible to retrieve an event log from a reverted transaction?).

  • Despite the misleading title, the question is not about events. – user19510 Apr 26 '18 at 13:27
  • Oh. Should I remove the answer? I don’t know the etiquette. – Thomas Jay Rush Apr 26 '18 at 14:51

The reason string is a very new addition to revert and require (about one week old). I believe that Geth's DebugTrace exposes the reason string, but otherwise I'm not sure there's tooling support yet.

I imagine that soon enough Etherscan will just surface them, but at the moment, reason strings are not particularly accessible to end users.

  • As I understand, if there is an exceptition, the TX is never mined and so it will never be present on Etherscan. Is that correct? – earizon Jun 11 '18 at 13:05
  • 1
    No, that's incorrect. Transactions that revert are still mined and still cost gas. – user19510 Jun 11 '18 at 13:06
  • 1
    Here's a recent transaction that reverted: etherscan.io/tx/…. – user19510 Jun 11 '18 at 13:07

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