Is it wrong to use auto_ptr with new char[n]

Question

If I declare a temporary auto deleted character buffer using

std::auto_ptr<char> buffer(new char[n]);

then the buffer is automatically deleted when the buffer goes out of scope. I would assume that the buffer is deleted using delete.

However the buffer was created using new[], and so strictly speaking the buffer should be deleted using delete[].

What possibility is there that this mismatch might cause a memory leak?

Answer 1

The behaviour of calling delete on a pointer allocated with new[] is undefined. As you assumed, auto_ptr does call delete when the smart pointer goes out of scope. It's not just memory leaks you have to worry about -- crashes and other odd behaviours are possible.

If you don't need to transfer the ownership of the pointer, Boost's scoped_array class might be what you're looking for.

Answer 2

I would use a vector of char as the buffer.

std::vector<char>    buffer(size);

read(input,&buffer[0],size);

Basically you don't even want to call new if you don't need to.
A vector provides a run-time sized buffer that you can use just like an array (buffer).

The best part is that the vector cleans up after itself and the standard guarantees that all element in the vector will be in contigious storage. Perfect for a buffer.

Or more formaly the guarantee is:

(&buffer[0]) + size == (&buffer[size])