# NSParameterAssert Validates the specified parameter. ``` #define NSParameterAssert(condition) ``` ## 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. This macro validates a parameter for an Objective-C method. Simply provide the parameter as the `condition` argument. The macro evaluates the parameter and, if it is false, it logs an error message that includes the parameter and then raises an exception. 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 [`func NSLogv(String, CVaListPointer)`](/documentation/Foundation/NSLogv(_:_:)) Logs an error message to the Apple System Log facility. [`extern void NSLog(NSString *format, ...);`](/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)