Which defensive coding principle involves verifying conditions before and after a function runs?

Which defensive coding principle involves verifying conditions before and after a function runs?

• A. Check functional preconditions and postconditions
• B. Use global variables
• C. Rely on exception handling alone
• D. Avoid assertions

Answer: (A)

Verifying conditions before and after a function runs is about defining and enforcing a contract for that function through preconditions and postconditions. Before execution, you check that inputs, state, and the environment meet expectations so the function isn’t forced to operate on invalid data. After execution, you verify that outputs and side effects satisfy what the function promised, ensuring invariants hold and the function hasn’t produced unexpected results. This approach helps you fail fast when something is wrong, prevents bad data from leaking through the system, and makes debugging easier because you know exactly where the contract was violated. In practice, assertions and guarded validations are common tools to implement these checks during development and to enforce reliability. Using global variables introduces hidden dependencies and makes reasoning about state harder, relying on exception handling alone doesn’t guarantee that the function’s contract is respected, and avoiding assertions removes a key mechanism for catching problems early.

Verifying conditions before and after a function runs is about defining and enforcing a contract for that function through preconditions and postconditions. Before execution, you check that inputs, state, and the environment meet expectations so the function isn’t forced to operate on invalid data. After execution, you verify that outputs and side effects satisfy what the function promised, ensuring invariants hold and the function hasn’t produced unexpected results. This approach helps you fail fast when something is wrong, prevents bad data from leaking through the system, and makes debugging easier because you know exactly where the contract was violated. In practice, assertions and guarded validations are common tools to implement these checks during development and to enforce reliability. Using global variables introduces hidden dependencies and makes reasoning about state harder, relying on exception handling alone doesn’t guarantee that the function’s contract is respected, and avoiding assertions removes a key mechanism for catching problems early.