ios下的精确定时（代码示例）

int main(int argcv, char *argv[])

{

    startTime = CFAbsoluteTimeGetCurrent();

}

-(void) applicationDidFinishLaunching(UIApplication *)app {

   dispatch_async(dispatch_get_main_queue(), ^{

     NSLog(@"Launched in %f sec", CFAbsoluteTimeGetCurrent() - startTime);

}