# Nonnull variable assignment violation Detects when you incorrectly assign null to a variable. ## Overview Use this check to detect when you assign `null` to a variable with the `_Nonnull` annotation. Available in Xcode 9 and later. > Note: The nonnull violation check for variable assignment is off by default. You can turn it on by enabling the `-fsanitize=nullability-assign` compiler flag. ### Violation of nonnull annotation with variable assignment in C In the following example, the call to `assigns_a_value` breaks the `_Nonnull` annotation of the variable `q`: ```occ void assigns_a_value(int *p) { int *_Nonnull q = p; // Warning: null can be assigned } assigns_a_value(NULL); // Error: _Nonnull variable violation ``` #### Solution Correct logic errors, or remove the `_Nonnull` annotation. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)