When do public member variables die?

Question

I have the following C++ class:

class DEF
{
   //...
}

class ABC
{
   public:
      DEF my_def;
      ~ABC();
   //...
}

And somewhere:

ABC* abc = new ABC(...);
delete abc;

My question:

Will my_def be accessible after calling delete abc? Is it safe to do abc->my_def.somefunc() after the delete? -

When data members die has nothing to do with whether they are public or not. — juanchopanza, Apr 18 '16 at 20:50
_"Is it safe to do abc->my_def.somefunc() after the delete?"_ No. That's undefined behavior. — πάντα ῥεῖ, Apr 18 '16 at 20:50
No. The object is deleted. If you want to keep `my_def` around, you should store it elsewhere. — Colin Basnett, Apr 18 '16 at 20:51
You should get a [good book on C++](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list?lq=1). You'll find out all about variable lifetimes there. — Rob K, Apr 18 '16 at 20:51
Accessible, yes, but the results of doing it are undefined. Safe? Absolutely not. Big no. — user4581301, Apr 18 '16 at 20:52
This would be like knocking down a house and expecting the second floor washroom to still be untouched and suspended in the air. — user4581301, Apr 18 '16 at 21:48

score 4 · Accepted Answer · edited May 23 '17 at 12:31

No, after abc's destructor ran, its members will be destroyed in reverse order of their declaration. When abc is deleted, all its memory is free'd. That includes my_def in your example.

Maybe this question will be useful to you: What is a smart pointer and when should I use one?

Addendum: One major problem with C++ is undefined behavior. Programming errors such as use-after-free may appear to work 80% of the time, if the memory was not reused in the meantime. But chances are that you overwrite unrelated memory and/or allow reading foreign data. That is a severe security problem, and a crashing program is the best you can hope for at this point.

@今天春天, you are mistaking C++ for a memory managed language such as Java or Python. Please read the answer in the linked question and look up any concept you don't understand. — Kijewski, Apr 18 '16 at 21:07

When do public member variables die?

1 Answers1