| name | pow10-rule-07-check-return-values |
| description | NASA Power of 10 Rule 7 — Check every non-void return value; validate every parameter. Severity: blocker. |
Rule 7 — Check Return Values & Validate Parameters
Severity: blocker
Statement
Check the return value of every non-void function. Validate every parameter at function entry, before any state mutation. Callers cannot be trusted, even within the same module.
Rationale
Ignoring a return value discards error information the callee computed. Unvalidated parameters let bad input propagate into corrupted state. Both checks isolate errors at their source.
Universal violation patterns
- Discarded non-void returns (
(void)foo(), _, _ = foo(), bare foo();)
- Function entry that mutates state before validating parameters
- Empty
catch / except blocks swallowing errors
Optional.get() / !! without prior null check- Errors crossing module boundaries unwrapped
Universal remediation pattern
At function entry, validate every parameter against domain constraints and reject (return error or raise) before any side effect. After every fallible call, check the return; on failure, propagate (with wrapping for traceability) and roll back any partial mutation.
Per-language guidance
Documented (void) casts
When you genuinely don't care about a return value (best-effort cleanup), state why:
(void)fclose(fp);
_ = file.Close()
Citations
- Holzmann 2006 — Rule 7
- CERT C — ERR33-C
