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I am creating a deconstructor, and I want to assert that my pointer float *queue is pointing to an array of floats. The compiler does not seem to like

assert([]queue);

and my program seg faults if I use

assert(queue != NULL); delete []queue;

. Thanks for the help.

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    No you cannot. I suggest you ask about your actual problematic code instead, since your question indicates that you have some fundamental design flaw in it. Commented Feb 9, 2020 at 0:16
  • you might research typeof and decltype, but that doesn't seem too helpful with just "a pointer" Commented Feb 9, 2020 at 0:20
  • Okay, well I am creating a queue from scratch for school. The queue's size is decided at run time, so I thought creating a dynamic array would be the best way to implement the code. I created a constructor that takes an argument for the size of queue, however, they want us to use a constructor with no arguments. Now, I know that MY driver code will always make an array, but I did not want to make an assumption that there will always be a new float [capacity] , when calling the deconstructor. @walnut Commented Feb 9, 2020 at 0:25
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    @Nate In practice, you should always use std::vector for that. If you are not allowed to use it, then new float[capacity] is correct. The queue should be a class and the queue pointer should be a private member of that class. Only the member functions that you implement should (be able to) change the pointer. This way you can be sure that it is always either a null pointer (when you set it to that) or a pointer to a float array allocated with new float[...]. No outside code should be allowed to change the pointer. Then you don't need the check that you are asking for. Commented Feb 9, 2020 at 0:30
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    @Nate Yes, you need to always initialize all non-class types with a sensible value, preferably immediately when you declare them (btw. since C++11 this works inside classes for class members as well). Only class types can have a default constructor that initializes to a reasonable initial value. Commented Feb 9, 2020 at 0:38

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No you cannot.

You can test whether a pointer has a null pointer value by comparing it against nullptr (or NULL in pre-C++11; NULL should never be used since C++11), but you can never tell whether a non-null pointer is pointing to a valid object, whether that object is part of an array or whether that object/array was allocated by new/new[].

It is the programmer's job to assure that the code can never reach a state where the above information is needed, but unavailable.

The easiest way of doing that is to never use raw new/delete. Instead only use std::vector and std::unique_ptr.

You also don't need to check for a null pointer before calling delete[]. delete[] can be called with a null pointer, in which case it simply doesn't do anything. You cannot call delete[] with a non-null pointer that doesn't have a value returned by new[] (and that hasn't been delete[]ed yet) tough. That would have undefined behavior.

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