Handling HBAR Transfers in Contracts

Overview

Sending to Contract

• transfer(): Sends a fixed amount of gas and reverts on failure.
• send(): Sends a fixed amount of gas and returns false on failure instead of reverting.
• call(): A low-level function for sending value that allows specifying gas and includes additional data payloads.

Key Considerations

• Fallback and Receive Functions: When sending HBAR to a contract address via contractCall, Hedera behaves like Ethereum. If receive() or fallback() functions are defined in the contract, they will be triggered upon receipt of HBAR.
• Important Note: Directly transferring HBAR to a contract’s Hedera account (not via contractCall) will not trigger these functions. To execute logic upon receipt, ensure transfers occur within the EVM environment.
• Amounts Are in Tinybars: Inside a contract, msg.value, address(this).balance, and the amount passed to transfer(), send(), or call{value: ...} are in tinybars (1 HBAR = 100,000,000 tinybars). An Ethereum literal such as 1 ether (10¹⁸) is 10¹⁰ HBAR on Hedera. See Decimal Handling.

Example Contract Functions for HBAR Transfers

// Handle incoming HBAR transfers
receive() external payable {
    // Example logic for received HBAR
    emit HbarReceived(msg.sender, msg.value);
}

// Transfer HBAR using different methods. _amount is in tinybars (1 HBAR = 100_000_000).
function transferHbar(address payable _receiverAddress, uint _amount) public {
    _receiverAddress.transfer(_amount);
}

function sendHbar(address payable _receiverAddress, uint _amount) public {
    require(_receiverAddress.send(_amount), "Failed to send HBAR");
}

function callHbar(address payable _receiverAddress, uint _amount) public {
    (bool sent, ) = _receiverAddress.call{value: _amount}("");
    require(sent, "Failed to send HBAR");
}

// Event for logging received HBAR
event HbarReceived(address sender, uint256 amount);

Additional Resources

• Hiero Contracts
• Solidity Documentation
• Solidity by Example