Question

I’m having a tricky debugging issue, perhaps due to my lack of understanding about how c++ manages memory. The code is too long to post, but the essential setup is as follows:

global_var = 0;
int main() {
  for(i = 0; i < N; ++i) {
    ClassA a;
    new ClassB(a); // seems to be problem!
  }
}

For some N, global_var gets corrupted (is no longer 0). There is nothing in the constructors of ClassA or ClassB that mess with global_var.

Replacing new ClassB(a) with ClassB b(a) seems to solve the problem, although this doesn’t allow me to do what I want (create a boost::ptr_vector with the new ClassB(a) instances).

Any ideas on what might be going wrong?

Update:
I’m really doing something like:

global_var = 0;
int main() {
  boost::ptr_vector<ClassB> myobjects;
  for(i = 0; i < N; ++i) {
    ClassA a;
    myobjects.push_back(new ClassB(a)); // seems to be problem!
  }
}

Both create problems. But why is this a problem? Should I be doing something else to put a bunch of objects into a queue? I’m using myobjects it as the basis of a Command Pattern.

Update

`classB’ looks like:

class ClassB {
public:
  ClassB() {}
  ClassB(ClassA a) : a_(a) {}
private:
  ClassA a_;
}

ClassA is just a simple list initialization as well (in real life).

Problem?

Update
I believe this may have something to do with the fact that global_var is actually a complex matrix type and there may be issues with the way it allocates memory.

Answer 1

After much exploration, this behavior turned out to be due to a bug in the underlying class of global_var. There was a subtle bug in the way global and static memory allocation was being done.