NSAssert

首先，NSAssert 是 foundation.framework 框架中的一个宏定义，作为断点检查的条件信息。如果给他一个 false 条件，会生成一个断点检查。

NSAssert

Generates an assertion if a given condition is false.

Declaration 声明

OBJECTIVE-C

#define NSAssert(condition, desc, ...)

Parameters 参数

condition	An expression that evaluates to YES or NO.   值为 YES 或 NO 的表达式
desc	An NSString object that contains a printf-style string containing an error message describing the failure condition and placeholders for the arguments.
...	The arguments displayed in the desc string.

Discussion

The NSAssert macro evaluates the condition and serves as a front end to the assertion handler. 

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 the method and class names (or the function name). It then raises an NSInternalInconsistencyException exception. If condition evaluates to NO, the macro invokes handleFailureInMethod:object:file:lineNumber:description: on the assertion handler for the current thread, passing descas the description string.

This macro should be used only within Objective-C methods. 

Assertions are disabled if the preprocessor macro NS_BLOCK_ASSERTIONS is defined.

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.