std :: reverse_iterator奇怪的行为（UB？）

Z时代
2024-01-10
分类：问答

我创建了一个伪容器类（它不包含任何元素）和一个此容器的迭代器类。下面的代码总是输出“776”我的系统上（我的编译器是gcc 5.4.0）std :: reverse_iterator奇怪的行为（UB？）

#include <iostream> 
#include <iterator> 
class Container 
{ 
public: 
    class Iterator; 
    Container()=default; 
    Container::Iterator begin(); 
    Container::Iterator end(); 
}; 
class Container::Iterator: public std::iterator<std::bidirectional_iterator_tag, size_t> 
{ 
public: 
    Iterator(size_t n); 
    size_t& operator*(); 
    Container::Iterator& operator--(); 
    const Container::Iterator operator--(int); 
    bool operator==(const Container::Iterator& rhs) const; 
    bool operator!=(const Container::Iterator& rhs) const; 
    private: 
    size_t n_; 
}; 
Container::Iterator Container::end() 
{ 
    return Iterator(777); 
} 
Container::Iterator::Iterator(size_t n): 
    n_(n) 
{ 
} 
size_t& Container::Iterator::operator *() 
{ 
    return n_; 
} 
Container::Iterator& Container::Iterator::operator--() 
{ 
    n_--; 
    return *this; 
} 
const Container::Iterator Container::Iterator::operator--(int) 
{ 
    Container::Iterator oldVal = *this; 
    n_--; 
    return oldVal; 
} 
int main() 
{ 
Container cont; 
std::reverse_iterator<Container::Iterator>revit(cont.end()); 
//as cppreference says, "For a reverse iterator r constructed from an iterator i, the relationship &*r == &*(i-1) is always true...", so I expect that the output must be the same as if I used instead next commented line, and it does so on my system 
    // auto it = cont.end(); it--; std::cout << *it << std::endl; 
    std::cout << *revit << std::endl; 
return 0; 
}