Events

Events are emitted by the EVM when certain actions are performed. They are defined in the contract code using the event keyword and can be emitted using the emit keyword.

You can add the attribute indexed to up to three parameters. These parameters are added to special data structure known as "Topics".

Topics allow you to search for events. Parameters without the indexed attribute are stored in the data section of the log.

pragma solidity ^0.8.0;

contract MyContract {
    // Define events
    event Transaction(address indexed sender, address indexed receiver, uint256 amount);
    event UserRegistered(address indexed user, string name);
    event UserUpdated(address indexed user, string name);
    event ContractPaused();
    event ContractResumed();

    // Struct to hold user data
    struct User {
        string name;
    }

    // Mapping from address to User data
    mapping(address => User) public users;

    // Variable to track whether the contract is paused
    bool public paused = false;

    // Function to transfer funds
    function transferFunds(address receiver, uint256 amount) public {
        (bool success, ) = receiver.call{value: amount}("");
        require(success, "Transfer failed.");

        // Emit the event to log the transaction
        emit Transaction(msg.sender, receiver, amount);
    }

    // Function to register a new user
    function registerUser(string memory name) public {
        users[msg.sender] = User(name);
        emit UserRegistered(msg.sender, name);
    }

    // Function to update a user's information
    function updateUser(string memory name) public {
        users[msg.sender].name = name;
        emit UserUpdated(msg.sender, name);
    }

    // Function to pause the contract
    function pauseContract() public {
        paused = true;
        emit ContractPaused();
    }

    // Function to resume the contract
    function resumeContract() public {
        paused = false;
        emit ContractResumed();
    }
}

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