[C++]C++小笔记之in-line function.

当一段程序被编译成一个执行程序后，它变成了一组机器语言指令。执行时，Operating System把这组指令加载到内存中，每段指令都有一个对应的内存地址。OS会一步一步的执行指令。当执行到一个function instruction时：

1. 程序保存当前内存地址，store function arguments to the stack, 然后jump到function的内存地址，starts to execute the function, reach to the end of the function and return to the stored memory address.

in-line function不用让程序跳到内存地址去访问function, in-line function 是在内存中直接读取。 Thus, it runs a little faster. 

To use in-line function:

1. use inline keyword to declare the function;

2. use inline keyword to define the function;

inline double Square(double x ) {return x*x;}

int main(){
double temp = Square(10);
}