Template class and arrays...

[PlasmaCube]

Okay, so, say I have a template class which holds a pointer to a dynamically allocated array. The type of the array is determined by the template.

What I need is a way to "erase" an item from the array. Specifically, the last item (which is easier because you don't have to move around values). Say I have this function:

template <typename T>
void SomeClass<T>::WeirdFunction()
{
  arrayPtr[endValue] = NULL;
}

where arrayPtr is a pointer to the array and endValue is an int which holds the subscript of the array's last element.

But since I don't know the type of the array, I can't just set it to NULL or 0 (what if it's a string?). I even tried allocating a new object of type T, and assigning it to the array's item, but that failed with an access violation error.

Any ideas?

[Bazzy]

Try with T(), it is the default value of 'T' but this shouldn't work if 'T' has only constructors which need some arguments.
You should try STL containers, some have a method called 'pop_back' which removes the last element

[daviddoria]

Use a std::vector and just resize it to length - 1.

[awasteoflife]

With a vector you could just use vector.erase or vector.pop_back anyway.

EDIT:

You should try STL containers, some have a method called 'pop_back' which removes the last element

Oops, didn't see that. meh.

[PlasmaCube]

Yeah, of course I would use an STL class for an actual implementation. After all, it'd be much more versatile than anything I could write up in time. The problem is that I was specifically asked to do it this way as an assignment...

And now that I think about it, I may have just had an off-by-one error on the pointer's subscript... I have another function that adds a value to the end of the array, and updates the endpoint marker, so I may have tried writing past the end of the array.

I'll try using T() when I get home. Would you just write it like:
arrayPtr[endValue] = T();

Or would I have to instantiate a temporary variable and then assign it to the array?

Thanks for the tips, guys!

[Bazzy]

If you don't need to create a new variable don't do it

[jsmith]

T() is the only way to do what you want generically, which requires default constructibility.

[PlasmaCube]

Hey everyone, thanks for posting.

Turns out it was a simple off-by-one error. I had forgotten to decrement the array endValue before using it as a subscript. I changed that, and used T(), and it worked perfectly.
Thanks again!