iOS:如何利用百度地图api计算两点间的实际距离?

小弟在做利用百度地图api计算两点间的距离的功能

官方就给了这三行代码:

BMKMapPoint point1 = BMKMapPointForCoordinate(CLLocationCoordinate2DMake(39.915,116.404));
BMKMapPoint point2 = BMKMapPointForCoordinate(CLLocationCoordinate2DMake(38.915,115.404));
CLLocationDistance distance = BMKMetersBetweenMapPoints(point1,point2);

可是复制-粘贴-报错,

错误提示: Implicit declaration of function 'BMKMapPointForCoordinate' is invalid in C99

什么情况?

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不好意思,忘了导头文件了,实在抱歉