Nulling Pointers After Deletion: Precautionary Measure or Potential Pitfall?

Nulling Pointers: A Precautionary Practice or a Hidden Hazard?

The practice of setting pointers to NULL after deleting them is often considered a good practice, but it's not as universally applicable as one might think.

In C , pointers can be set to NULL to avoid potential crashes caused by double deletes. When a pointer is set to NULL, any subsequent attempts to delete it will be harmless. This is in contrast to deleting a pointer that has already been deleted, which can lead to undefined behavior.

Consider the following example:

Foo* foo = 0; // Sets the pointer to NULL
delete foo; // Won't do anything

Here, the pointer is initially set to NULL, so attempting to delete it will have no effect.

However, if the pointer is not set to NULL:

Foo* foo = new Foo();
delete foo; // Deletes the object
delete foo; // Undefined behavior

The second delete operation will cause undefined behavior because the pointer has already been deleted and the memory it pointed to has been freed.

While nulling pointers after deletion can prevent crashes, it can also mask double delete bugs, leaving them unhandled. It's better to avoid double delete bugs altogether, but in practice, this can be difficult.

Smart pointers provide a solution to this issue by managing memory automatically, eliminating the need for manual deletion. However, for legacy code or in specific scenarios where manual memory management is preferred, nulling pointers after deletion can help prevent crashes but should be used cautiously.

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