Pointers stored in the list getting corrupted??

[bmsce engg]

Hi,
Have been struggling to find the reason for this occasional problem with pointers that I am storing in a list (STL C++).
My class name is : Tamper

All I do is this:

1- Instantiate Tamper with new and push the address in a list of type Tamper. The number of pushes are huge, may be in hundreds (dont think it matters as long as i have space).

Tamper *ptr=new Tamper();
list<Tamper *> = mylist;
mylist.push_back(ptr);

2- At a later point, I simply use list iterators and retrieve the stored pointers and call "delete" on them, which sounds straight forward and it works fine for me. But once in a while, I see that my process dumps core with SIGSEGV or SIGBUS, and stack points to "delete" operation.

list<Tamper *>::iterator it = mylist.begin();

for(; it != mylist.end() ; ++it)
{
delete *it;
*it=0;
}

How do I get rid of this occasional but consistent problem while freeing the memory. I don't think I am trying to release someone else's memory.

Appreciate your help here.

[weaknessforcats]

What you show is straightforward. You delete pointers you allocated and you set those deleted pointers to zero to avoid an exception by deleting them again.

Are you sure you never pushed a local pointer? That wil do it every time.

Is this a multi-threaded program? If so, the delete and he subsequent setting of the pointer to zero is no thread safe.

[bmsce engg]

Thanks for your reply first of all!!!
This is not multithreaded, and there is no pushing of local pointer. I already did something like this just to make sure I am deleting my own pointers:

for(; it != mylist.end() ; ++it)
{
if ( typeid(*it) == typeid(Tamper *) )
{
delete *it;
*it=0;
}
}


This works in a similar way as before. But dumps core as usual.

The point here is, somehow the addresses are getting corrupted.
- Is there a better way to validate the address before deleting?
- Could there be environment issue here?

[weaknessforcats]

I ran your code for 1000 pointers and failed to produce a crash.

There's something else going on that's not in the code you have shown. Using naked pointers in C++ is very dangerous. The Tamper* should be a handle object.

There is no way to validate an address. The most you can do is say that a zero address is invalid. All non-zero addresses are presumed valid.

Is there by chance a delete of the Tamper* somewhere else in the code and at that place the pointer is not set to zero?

[mac11]

I think you'd be better off having your list hold smart pointers (such as boost::shared_ptr). Then you don't have to explicitly delete anything and are much less likely to run into problems with raw pointers.

For an example see:
http://www.boost.org/doc/libs/1_46_1...tr_example.cpp

[bmsce engg]

Thanks for your answer.
I will check and make sure I am not deleting this address somewhere else, though I am sure I am not doing it.
I will come back to you weaknessforcats after some more check.

[bmsce engg]

Thanks mac11... I will check the possibility of using boost shared ptrs.