Deleting a pointer in C++

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1 & 2

myVar = 8; //not dynamically allocated. Can't call delete on it.
myPointer = new int; //dynamically allocated, can call delete on it.

The first variable was allocated on the stack. You can call delete only on memory you allocated dynamically (on the heap) using the new operator.

3.

  myPointer = NULL;
  delete myPointer;

The above did nothing at all. You didn’t free anything, as the pointer pointed at NULL.

The following shouldn’t be done:

myPointer = new int;
myPointer = NULL; //leaked memory, no pointer to above int
delete myPointer; //no point at all

You pointed it at NULL, leaving behind leaked memory (the new int you allocated).
You should free the memory you were pointing at. There is no way to access that allocated new int anymore, hence memory leak.

The correct way:

myPointer = new int;
delete myPointer; //freed memory
myPointer = NULL; //pointed dangling ptr to NULL

The better way:

If you’re using C++, do not use raw pointers. Use smart pointers instead which can handle these things for you with little overhead. C++11 comes with several.

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  2. Is it safe to delete a NULL pointer?
  3. How does delete[] know it’s an array?
  4. Is there any reason to check for a NULL pointer before deleting?
  5. Is the pointer guaranteed to preserve its value after `delete` in C++?
  6. What happens when you deallocate a pointer twice or more in C++?
  7. Why is sizeof giving incorrect number of bytes in C++?
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  9. Passing a 2D array to a C++ function
  10. What exactly is nullptr?
  11. Is delete[] equal to delete?
  12. Testing pointers for validity (C/C++)
  13. Why does cout print char arrays differently from other arrays?
  14. Why aren’t pointers initialized with NULL by default?
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  18. Convert C++ function pointer to c function pointer
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  27. Is the whole object freed with a non-virtual destructor and a Base class pointer?
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