百思不得其解,于是百度,google吧。。
发现*上也有人有相同的问题
下面是他的问题:
For my compsci class, I am implementing a Stack template class, but have run into an odd error:
Stack.h: In member function ‘
const T Stack<T>::top() const
[with T = int]’:Stack.cpp:10: error: passing ‘
const Stack<int>
’ as ‘this
’ argument of ‘void Stack<T>::checkElements()
[with T = int]’ discards qualifiers
Stack<T>::top()
looks like this:
const T top() const {
checkElements();
return (const T)(first_->data);
}
Stack<T>::checkElements()
looks like this:
void checkElements() {
if (first_==NULL || size_==0)
throw range_error("There are no elements in the stack.");
}
The stack uses linked nodes for storage, so first_
is a pointer to the first node.
Why am I getting this error?
正确答案是
Your checkElements()
function is not marked as const
so you can't call it on const
qualified objects.
top()
, however is const qualified so in top()
, this
is a pointer to a const Stack
(even if theStack
instance on which top()
was called happens to be non-const
), so you can't callcheckElements()
which always requires a non-const
instance.
意思是说 在一个加了const限定符的成员函数中,不能够调用 非const成员函数。
因为如果调用了非const成员函数,就违反了const成员函数不改变对象的规定。
而error:...discards qualifiers 的意思就是缺少限定符
因此,他的解决办法很简单了 ,只要将checkElements()函数申明改为 checkElements()const就行了