How do we know if a pointer was allocated with new or new[]?

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I'm trying to implement a unique_ptr class in C++, but how to know if the pointer we passed to it was allocated with new or new[] without using default_delete (my school standard doesn't allow c++11). I mean when you pass your pointer to the constructor like this for example:

unique_ptr<int> ptr(new int[10]);

how do you know inside of the class if you need to call delete[] or delete ?

c++
1 Answers

You can't tell. And neither can std::unique_ptr.

Think about it. If it could be determined automatically, you wouldn't need two kinds of delete.

std::unique_ptr<int> ptr(new int[10]); is wrong, since it will call delete, rather than delete[].

Use std::unique_ptr<int[]> ptr(new int[10]); instead, which will call delete[], rather than delete.

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