CODEWITHSUNDEEP
c++visual-c++access-violation
Mafahir Fairoze
Mafahir Fairoze

Reputation: 697

How to detect and isolate C++ Access Violation Error

While i was developing a C++ application,

I was using a simple list<int> *somelist = new list<int>(); that contains data.

I was trying to iterate this list using something like this:

for (list<int>::iterator j=somelist->begin();j!=somelist->end();j++)
{
    //do something with *j
}

When i was doing something with the pointer j because of a chain reaction the data that i was going to access was removed from the list and no longer exists.

So, i am being prompted with an Access Violation Error Msg.

Can someone tell me how to identify if the pointer j is a bad ptr

Upvotes: 1

Views: 1150

Answers (3)

Jaywalker
Jaywalker

Reputation: 3119

With multi-threading your iterator can become invalidated if some other thread removes elements from the list. With a low-level programming such as C++, there is no way to detect this problem once it has happened. Your best bet is to "prevent this from happening."

Use synchronization functions (e.g., WaitForSingleObject in Windows) to control access to shared STL containers.

Upvotes: 0

Johannes Schaub - litb
Johannes Schaub - litb

Reputation: 507413

The bug in your code is that you need to handle this when you still know you removed it. Afterwards you cannot handle it anymore. In the following example, dosomething returns true when the element should be removed

for (list<int>::iterator j=somelist->begin();j!=somelist->end();) {
   if(dosomething(j)) {
     /* should remove it! */
     j = somelist->erase(j);
   } else {
     ++j;
   }
}

Upvotes: 1

Puppy
Puppy

Reputation: 147056

Can't be done. You have to not delete the list during traversal.

Upvotes: 1

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