# NSCAssert Generates an assertion if the given condition is false. ``` #define NSCAssert(condition, desc, ...) ``` ## Discussion Assertions evaluate a condition and, if the condition evaluates to false, call the assertion handler for the current thread, passing it a format string and a variable number of arguments. Each thread has its own assertion handler, which is an object of class `NSAssertionHandler`. When invoked, an assertion handler prints an error message that includes method and class names (or the function name). It then raises an `NSInternalInconsistencyException` exception. The `NSCAssert` macro evaluates the condition and serves as a front end to the assertion handler. This macro should be used only within C functions. `NSCAssert` takes no arguments other than the condition and format string. The `condition` must be an expression that evaluates to true or false. `description` is a printf-style format string that describes the failure condition. Assertions are disabled if the preprocessor macro `NS_BLOCK_ASSERTIONS` is defined. All assertion macros return void. > Important: > Do not call functions with side effects in the `condition` parameter of this macro. The `condition` parameter is not evaluated when assertions are disabled, so if you call functions with side effects, those functions may never get called when you build the project in a non-debug configuration. > Note: > Not all release configurations disable assertions by default. ## See Also [`NSLogv`](/documentation/Foundation/NSLogv(_:_:)) Logs an error message to the Apple System Log facility. [`NSLog`](/documentation/Foundation/NSLog) Logs an error message to the Apple System Log facility. --- 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)