调试函数耗时的利器CFAbsoluteTimeGetCurrent

    CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();    // do something    CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();    NSLog(@"time cost: %0.3f", end - start);

类型说明：
CFAbsoluteTime为double类型

typedef double CFTimeInterval;typedef CFTimeInterval CFAbsoluteTime;/* absolute time is the time interval since the reference date *//* the reference date (epoch) is 00:00:00 1 January 2001. */