Cyfrin Updraft is an education platform specializing on teaching the next generation of smart contract developers 

Cyfrin Updraft

![](https://ipfs-cdn.peeranha.io/QmXVPMEEKxAfiNHbrUbByDq5T8PV2j1Xg6qNENw1b5fpVG)
**Understanding Topics in Ethereum Smart Contracts: Event Logs and Their Importance**

In the world of Ethereum smart contracts, **topics** play a pivotal role within event logs, helping developers and applications identify and filter specific events efficiently. These mechanisms are integral to the functioning of decentralized applications (dApps). They facilitate seamless interaction with the Ethereum blockchain. Let's delve deeper into the concept of topics and their significance.

### What Are Topics in Ethereum Smart Contracts?

In Ethereum, smart contracts can emit events to signal that something of interest has happened within the contract. These events are logged on the blockchain, and topics are used within these event logs to categorize and filter the logged data. Topics are essentially indexed fields that make it easier to find and analyze specific events.

### Breakdown of Topics and Their Uses

**1. Event Identification**  
The first topic, commonly known as **Topic0**, is the **Keccak256 hash of the event signature**. This signature includes the event's name and the types of its input parameters. By using this hash, the Ethereum network can distinguish one event from another, ensuring that each event is uniquely identifiable. This is crucial for accurate event tracking and logging.

**2. Indexed Parameters**  
When defining events in smart contracts, developers can mark certain parameters as **indexed**. These indexed parameters become additional topics (e.g., Topic1, Topic2, etc.). Indexing parameters allow for efficient searching and filtering of events. For example, in a token transfer event, indexing the sender and recipient addresses enables quick identification of all transactions involving a specific address.

**3. Data Storage**  
Parameters that are not marked as indexed are stored in the **data section** of the event log. Unlike indexed parameters, these data values are not searchable as topics but contain the actual values of the event parameters. This separation ensures that only the most relevant and frequently searched data is indexed, optimizing storage and retrieval.

**4. Efficient Filtering**  
One of the primary advantages of topics is the ability to **filter and listen for specific events**. External applications, such as wallets or dApps, can subscribe to events and use topics to filter the events they are interested in. For instance, a decentralized exchange (DEX) can listen for events related to token swaps, while ignoring other unrelated events. This targeted filtering enhances performance and reduces the amount of data that needs to be processed.

### Practical Applications of Topics in Ethereum

The use of topics in event logs has numerous practical applications, making it easier for developers and users to interact with the Ethereum blockchain. Here are a few examples:

- **Token Transfers**: By indexing the sender and recipient addresses in token transfer events, wallets can quickly display transaction histories to users.
- **Decentralized Exchanges**: DEX platforms can filter events to track specific trading pairs, ensuring efficient matching and execution of trades.
- **Governance and Voting**: In decentralized autonomous organizations (DAOs), topics can be used to monitor and verify voting results and proposals.

### Conclusion

In summary, topics in Ethereum smart contract logs are essential for efficiently identifying, filtering, and processing events. They enable quick retrieval and analysis of blockchain data, making it easier for applications to interact with the Ethereum network. By leveraging the power of topics, developers can create more responsive, efficient, and user-friendly decentralized applications.

Topics in Ethereum smart contracts

hi, iam new to this web3 development i started cyfrin updraft course couple of weeks ago. iam trying to follow the instructor and deploy on sepolia testnet but iam getting high gas fee of about 0.4 eth, what should i do please?

Sepolia testnet requires high gas fee

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Vyper

Functionland is replacing Cloud Storage and Service Subscription economy by introducing a new category of products, called Blockchain-Attached Storage. It creates value by auto-minting crypto for the users and allocating a share to the developers.

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Fractal Visions

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D_D Academy

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The Graph

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Polygon

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Big thanks to Cyfrin Updraft for this awesome opportunity! Super grateful for the chance to level up my Solidity skills with such an amazing team. Excited for what’s ahead—time to deploy and make an impact! 🚀

Blockchain developer appreciation

Hi all, I'm about to complete the solidity course and to begin the blockchain security course.

In order to envision myself working as an auditor, can you share what are the most common tasks that smart contract auditors are required to perform on a daily basis on any regular job?

How is a day of a smart contract auditor working day like since he starts until he finishes?

Does his boss request to work on a specific protocol during that day or during a whole week and to send an audit report at the end of the day or week? and like this every week but with different code snippets or entire protocols?

Many thanks

Smart Contract Auditor

Hi everyone,

I’m thrilled to share that I’m a new learner who has just completed a Solidity 101 course. The journey so far has been incredibly exciting and insightful. I’m eager to continue exploring and deepening my knowledge in Solidity and blockchain development. Looking forward to engaging with this amazing community and learning together!

I’m curious to know what resources have helped others at my level improve. Any recommendations on websites, courses, tools, or any other materials would be greatly appreciated.

Cheers,
Philip

Excited to Continue Learning Solidity!

Hello everyone , I've noticed that the offer function uses the .call{value: amount}("") method to send Ether to the recipient's address.

Could anyone provide insight into whether this function is indeed vulnerable to reentrancy and suggest any best practices or modifications to mitigate such risks?

```solidity 
function _offer(address to, uint256 amount) internal {

      balance -= amount;

      (bool success, ) = to.call{value: amount}("");
      if (!success) {
          revert TransferFailed(address(0), address(this), to, amount);
      }
  }
```

Reentrancy Vulnerability

Test Question for Cyfrin Updraft

I'm getting this error when clicking on the getBalance button of the live page of port 5500 for my anvil:

"BlockOutOfRangeError: block height is 150 but requested was 12092"

![](https://example.com/your-image.png)![](https://ipfs-cdn.peeranha.io/QmT9GJ949XC34CUGzCLAL2QyZoSXABMesC2rELvxrBZx6r)

Can anyone help explain what I missed here? Thank you!

BlockOutOfRangeError

While trying to set my foundry after installing using the "forge init" command, i got this error:

Error: failed to commit (code=Some(128), stdout="", stderr="Author identity unknown\n\n*** Please tell me who you are.\n\nRun\n\n  git config --global user.email \"you@example.com\"\n  git config --global user.name \"Your Name\"\n\nto set your account's default identity.\nOmit --global to set the identity only in this repository.\n\nfatal: unable to auto-detect email address (got 'user@MACs-MBP.(none)')")

Though I was able to get all the folder I needed, except from "lib" and ".gitmodules" hope this won't affect me in future. And i also try using the "forge init --force" still the same

Setting Foundry

Why do i keep getting this error when trying to deploy my code in VS code, asked AI and it's still the same. Here is the error:
[⠊] Compiling...
[⠢] Compiling 14 files with Solc 0.8.18
[⠆] Solc 0.8.18 finished in 149.20ms
Error: Compiler run failed:
Error (2314): Expected ';' but got identifier
  --> script/DeploySimpleStorage.s.sol:11:9:
   |
11 |         vm.stopBroadcast();
   |         ^^



And here is my code. solidity
'''
// SPDX-License-Identifier: MIT

pragma solidity ^0.8.18;
import {Script} from "forge-std/Script.sol";
import {SimpleStorage} from "../src/SimpleStorage.sol";

contract DeploySimpleStorage is Script {
    function run() external  returns (SimpleStorage) {
        vm.startBroadcast();
        SimpleStorage simpleStorage = new SimpleStorage();
        vm.stopBroadcast();
        return simpleStorage;
    }
}
'''

Setting up SimpleStorage Deployer

seems the zksync foundry installation, isn't in the github repo anymore, i tried to type the command line into my terminal "permission denied, could not read from remote repository"

Zksync Foundry Install

What could wrong in my code?
```
 function testFundUpdatesFundedDataStructure() public {
        fundMe.fund{value: 10e18}();
        
        uint256 amountFunded = fundMe.getAddressToAmountFunded(address(this));
        assertEq(amountFunded, 10e18);
    }```

getting  this error:

 [14658] FundMeTest::testFundUpdatesFundedDataStructure()
    ├─ [2658] FundMe::fund{value: 1000000000000000000}()
    │   ├─ [0] 0x0000000000000000000000000000000000000000::latestRoundData() [staticcall]
    │   │   └─ ← [Stop] 
    │   └─ ← [Revert] EvmError: Revert
    └─ ← [Revert] EvmError: Revert

Discussions

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