这个构造函数代码如何将指针作为参数？

The code below has three arguments of the type double*. The code is part of an Arduino PID library and the user would typically give a reading of an analogue port or some kind of sensor as the argument for the "input" term and some fixed value or user controlled variable as the value of the "setpoint" term. But the argument is of type double*. Shouldn't the user get an error when he provides a double?The code below has three arguments of the type