Virtual function invoking segmentation fault

Question

I am getting a segmentation fault whenever I am trying to access a virtual function. The code is basically like this:

class Super {
  public:
    Super() { cout << "Ctor Super" << endl; }
    virtual void test() = 0;
  };

class Sub : public Super {
  public:
    Sub() { cout << "Ctor Sub" << endl; }
    void test() { cout << "Test in Sub" << endl; }
  };

void main()
 {
   Super* s = new Sub;
   s->test(); // Segmentation fault So I tried the one below

   Sub* s1 = new Sub;
   s1->test(); //Still segmentation fault

   Sub s2;
   s2.test(); // Works fine BUT

   Super *s3 = &s2;
   s3->test(); // segmentation fault and EVEN

   Sub *s4 = &s2;
   s4->test(); //segmentation fault
 }

I have tried almost everything I know about virtual functions and it does not work. It's actually a part of a bigger program so it might have some problem there but as soon as I remove the virtual function or stop making it virtual it works. Any Ideas?

Also is there any tool or way to examine the vtable?

yups it should, but its not on my machine. I am running it on a LYnxOS powerPC machine. Can you think of any situation where it should not run. — Rohit Chauhan, Apr 11 '11 at 04:06

score 0 · Answer 1 · answered Apr 10 '11 at 12:00

0

Class Sub does not inherit from class Super, so they aren't related in any way as currently written.

answered Apr 10 '11 at 12:00

Joe

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score 0 · Answer 2 · answered Apr 10 '11 at 12:01

0

Can this code compile at all?

All your methods are private.
There is no inheritance between Sub and Super.
The constructor are wrongly named.
The main() function does not return int.

Fixing all these results in a code that compiles and runs without a segfault.

answered Apr 10 '11 at 12:01

adl

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Yes this code compiles and executes.. that is why I am getting a seg fault. Its a c++ code, I think you are confusing it with some other language (java probably....). Anyway help if you find someting... cheers. – Rohit Chauhan Apr 11 '11 at 04:05
The code did not look the way it looks now when I (and Joe) answered. The first three points have been fixed. It is still invalid C++ because main() should return int (http://stackoverflow.com/questions/204476/what-should-main-return-in-c-c), but that would not justify a segfault. – adl Apr 11 '11 at 06:15

score 0 · Answer 3 · answered Apr 11 '11 at 07:10

I don’t see what could cause the problem except a compiler bug. Can you give the exact compiler version?

In the meantime, I would try the following:

add a dummy int member to the classes. It might be that a zero-sized class causes wrong code generation.
declare Sub::test() as virtual, too. Again, might be the compiler misbehaving here.

Also, what kind of segmentation fault are you getting? Is it precisely SIGSEGV or is it another signal? Could you give a debugger backtrace and local assembly dump?

Virtual function invoking segmentation fault

3 Answers3