# Invalid Boolean value Detects when a program accesses a Boolean variable and its value isn’t true or false. ## Overview Use this check to detect accesses to a Boolean variable when its value isn’t true or false. This problem can occur when using an integer or pointer without an appropriate cast. The use of out-of-range Boolean values has undefined behavior, which can be difficult to debug. Available in Xcode 9 and later. ### Invalid Boolean variable access in C The intent of the following code is to call the `success` function when `result` is nonzero. However, because it uses a Boolean check, the compiler may, as an optimization, only emit instructions that check the least-significant bit of `predicate`, which is `0`, causing a logic error. ```occ int result = 2; bool *predicate = (bool *)&result; if (*predicate) { // Error: variable is not a valid Boolean success(); } ``` #### Solution Use integer comparison instead of a Boolean check. ```occ int result = 2; if (result != 0) { // Correct success(); } ``` --- 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)