#define NSAssert(condition, desc)
condition是条件表达式，值为YES或NO；desc为异常描述，通常为NSString。当conditon为YES时程序继续运行，为NO时，则抛出带有desc描述的异常信息。NSAssert()可以出现在程序的任何一个位置。具体事例如下：
生成一个LotteryEntry对象时，传入的NSDate不能为nil，加入NSAssert()判断。对象初始化源码如下：
- (id)initWithEntryDate:(NSDate *)theDate {
self = [super init];
if (self) {
NSAssert(theDate != nil, @"Argument must be non-nil");
entryDate = theDate;
firstNumber = (int)random() % 100 + 1;
secondNumber = (int)random() % 100 + 1;
}
return self;
}
接下来则是生成对象时传入一个值为nil的NSDate，看断言是否运行。
LotteryEntry *nilEntry = [[LotteryEntry alloc] initWithEntryDate:nil];
断言效果如下：
2013-01-17 20:49:12.486 lottery[3951:303] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Argument must be non-nil'
*** First throw call stack:
(
0 CoreFoundation 0x00007fff90c590a6 __exceptionPreprocess + 198
1 libobjc.A.dylib 0x00007fff8fd2a3f0 objc_exception_throw + 43
2 CoreFoundation 0x00007fff90c58ee8 +[NSException raise:format:arguments:] + 104
3 Foundation 0x00007fff88dae6a2 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 189
4 lottery 0x0000000100001929 -[LotteryEntry initWithEntryDate:] + 249
5 lottery 0x0000000100001794 main + 932
6 libdyld.dylib 0x00007fff8d83f7e1 start + 0
)
libc++abi.dylib: terminate called throwing an exception