Re: The C++ Language 4th edition - Subclassing vector for range checking.

From:

SG <s.gesemann@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 16 Jul 2013 01:26:33 -0700 (PDT)

Message-ID:

<c2f44d5c-6515-4619-b014-9ba5d692c5eb@googlegroups.com>

On Sunday, July 14, 2013 3:26:45 AM UTC+2, mrile...@gmail.com wrote:

In The C++ Programing Language 4.4.1.2 Stroustrup says "... I often
use a simple range-checking adaption of vector:"

template<typename T>
class Vec : public std::vector<T> {
public:
    using vector<T>::vector;

    T & operator[](int i)
        {return vector<T>::at(i);}

    const T & operator[](int i) const
         {return vector<T>::at(i);}
};

I thought this was some what dangerous because if an user of the class
(Maybe not the person who wrote it) writes:

Vector<T> * vectorObject = new Vec<int>(100);
delete vectorObject;

Results in undefined behavior.

Did something change in C++11?

No. Using delete in this case still invokes undefined behaviour. You
can think of what Stroustrup is doing as a hack. It works as long as
you don't use delete in such a way.

I find it a bit unfortunate that Stroustrup suggests something like
this. I find it unfortunate that he does not mention that at least two
popular C++ implementations (G++ and MSVC) provide extra debugging
features. For example, see

<http://gcc.gnu.org/onlinedocs/libstdc++/manual/debug_mode.html>
(debug mode of the standard library implementation)