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  • Solidity Interview – Overflow/Underflow Handling?

    Merry Wordsworth

    Member

    Updated: May 8, 2025
    Views: 1.1K

    I’m preparing for a Solidity interview and need help understanding how to best handle overflow/underflow issues. Should I rely solely on Solidity's built-in checks, or is using SafeMath (like from OpenZeppelin) still relevant—especially in upgradable contracts and during version changes?

    Three days ago, I gave an interview and got stuck on questions related to overflow and underflow in Solidity. I’d appreciate more clarity on Solidity’s built-in safeguards, any known edge cases where extra caution is required, and performance implications of different approaches.

    Also, if you have tips or examples—particularly around upgradable contracts and managing overflow risks across compiler versions—I’d be grateful. Thanks in advance!

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  • Sayali Bhandari

    Member • 7mos

    To handle integer overflow and underflow in a Solidity smart contract, follow these steps:

    1. Use Solidity 0.8.0 or Later: These versions include built-in checks that automatically revert transactions when an overflow or underflow occurs. This simplifies error handling and secures calculations.

    2. Identify Critical Operations: Review arithmetic functions to pinpoint areas where overflows or underflows are likely, such as loops, multiplications, or calculations involving user inputs.

    3. Apply unchecked Only When Necessary: For performance-critical operations, use the unchecked block to bypass built-in checks. Do this only when you are confident that values remain within safe limits after rigorous testing.

    4. Validate Inputs and Outputs: Add require statements to verify that inputs and outputs are within the expected range. This provides an additional layer of safety against invalid data.

    5. Test Edge Cases: Use testing frameworks like Hardhat or Foundry to simulate extreme scenarios, such as maximum or minimum integer values, to ensure the contract behaves as expected.

    6. Use Libraries for Older Versions: If using a version below 0.8.0, integrate libraries like OpenZeppelin’s SafeMath to manage arithmetic safely.

    7. Check Upgradable Contracts: For upgradable smart contracts, ensure that arithmetic logic remains consistent between versions and thoroughly test interactions across upgrades.

    Following these steps ensures that your Solidity smart contract handles integer vulnerabilities effectively while maintaining efficiency and security.

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  • Shubhada Pande

    Community Administrator • 1mo

    For more interview questions, read our blog https://artofblockchain.club/article/top-30-interview-questions-for-senior-solidity-developers-in-2025

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