push_back(this) pushes wrong pointer onto vector - c++

Question

I have a vector of UnderlyingClass pointers stored in another object, and inside a method in UnderlyingClass I want to add the "this" pointer to the end of that vector. When I look at the contents of the vector immediately after the push_back call, the wrong pointer is in there. What could be going wrong?
cout << "this: " << this << endl;
aTextBox.callbacks.push_back(this);
cout << "size is " << aTextBox.callbacks.size() << endl;
cout << "size-1: " << aTextBox.callbacks[aTextBox.callbacks.size()-1] << endl;
cout << "back: " << aTextBox.callbacks.back() << endl;
cout << "0: " << aTextBox.callbacks[0] << endl;
cout << "this: " << this << endl;
cout << "text box ptr: " << &aTextBox << endl;
cout << "text box callbacks ptr: " << &(aTextBox.callbacks) << endl;
Here's the output:
this: 0x11038f70
size is 1
size-1: 0x11038fa8
back: 0x11038fa8
0: 0x11038fa8
this: 0x11038f70
text box ptr: 0x11039070
text box callbacks ptr: 0x11039098
By the way, callbacks is a vector of WebCallback pointers, and UnderlyingClass implements WebCallback:
std::vector<WebCallback*> callbacks;
class UnderlyingClass
:public WebCallback
Copied from comments: (see Answer below)
output:
this: 0x6359f70
size is 1
size-1: 0x6359fa8
back: 0x6359fa8
0: 0x6359fa8
this: 0x6359f70
WebCallback This: 0x6359fa8
text box ptr: 0x635a070
text box callbacks ptr: 0x635a098
okay, so that explains why the pointers don't match up.
My real question, then, is this:
how do I get the correct version of a method to be called? Specifically, WebCallback stipulates that a function onWebCommand() be implemented, and right now callbacks[0]->onWebCommand() is not causing the onWebCommand() that I wrote in UnderlyingClass to be executed.

Answer 1

This can happen with multiple inheritance, if your layout looks like this:
class UnderlyingBase {
char d[56];
};
class UnderlyingClass
:public UnderlyingBase,
public WebCallback {
};
Then the layout can be like this, for each object involved. The last one is the complete object containing the first two ones as base-class sub-objects, and that you take the pointer of, and which will be converted to WebCallback*.
[UnderlyingBase]
> char[56]: 56 bytes, offset 0x0
[WebCallback]
> unknown: x bytes, offset 0x0
[UnderlyingClass]
> [UnderlyingBase]: 56 bytes (0x38 hex), offset 0x0
> [WebCallback]: x bytes, offset 0x38
Now since your vector contains WebCallback*, the compiler adjusts the pointer to point to the WebCallback sub-object, while when it would point to UnderlyingClass or UnderlyingBase, it would start 0x38 (56) bytes earlier.

Answer 2

Add this to your print out:
cout << "this: " << this << endl;
cout << "WebCallback This: " << dynamic_cast<WebCallback*>(this) << endl;
I bet this is what you are looking for.