函数头/原型中const关键字的使用类型有什么区别？

Question

What is the difference between the various usages of the const keyword in the function header/prototype?

    const int function(const int x) const;

Answer:

The 1st const is to return by constant value shown here .

The 2nd const is to have a constant function parameter shown here .

The 3rd const is used when the function is a class method/function that should only perform some sort of query operation such as get, hence should not change any of the class attributes/data variables shown here .

Answer 1

const E& top() const throw(StackEmpty);

const E& is the return type of the function top() . It is a reference to a constant E .

The const after the name of the function specifies, that the function won't modify the instance it is called upon and thus can be called on const -qualified instanced of the struct / class , top() is a member of.

The throw() -specification tells, that top() may throw an object of type StackEmpty . AFAIK such throw() -specifications naming a specific type are depreciated since C++11.